Nonvolatile latch circuit and logic circuit, and semiconductor device using the same

The disclosed invention relates to a non-volatile logic circuit in which the stored logic state is not erased even when the power is turned off, and a semiconductor device using the same. In particular, the present invention relates to a non-volatile latch circuit and a semiconductor device using the same.

An integrated circuit that integrates non-volatile logic that incorporates the property of "nonvolatile", which does not erase memory even when the power is turned off, has been proposed. For example, a non-volatile latch circuit using a ferroelectric element as non-volatile logic has been proposed (Patent Document 1).

<p><patcit num="1"><text>International Publication No. 2003/044953</text></patcit></p>

<p>However, a non-volatile latch circuit using a ferroelectric element has problems in reliability of the number of rewrites and reduction in voltage. Further, the ferroelectric element is polarized by the electric field applied to the element, and information is stored when this polarization remains. However, if this residual polarization is small, the influence of variation in the amount of charge becomes large, and a high-precision readout circuit is required.</p><p>In view of such a problem, one of the problems of the present invention is to provide a novel non-volatile latch circuit and a semiconductor device using the same.</p>

<p>One embodiment of the present invention has a loop structure in which the output of the first element is electrically connected to the input of the second element and the output of the second element is electrically connected to the input of the first element. It has a latch portion and a data holding portion for holding data of the latch portion, and the latch portion and the data holding portion form a non-volatile latch circuit. The data holding unit uses a transistor using an oxide semiconductor as the semiconductor material constituting the channel forming region as the switching element.</p><p>It also has a capacitance electrically connected to the source electrode or drain electrode of this transistor. Using the above transistor, the data held in the latch section can be written to the capacitance of the data holding section. Further, the above-mentioned transistor can be used to hold the written data in the capacitance of the data holding unit. Further, by using the above-mentioned transistor, the data held in the capacitance of the data holding unit can be read out to the latch unit.</p><p>That is, one embodiment of the present invention has a latch portion and a data holding portion that holds data in the latch portion. The data holding unit has a transistor and a capacitance, the channel forming region of the transistor has an oxide semiconductor layer, and one of the source electrode and the drain electrode of the transistor is electrically connected to one electrode of the capacitance. The other of the source electrode and the drain electrode of the transistor is electrically connected to the latch portion to form a non-volatile latch circuit.</p><p>In the above, the latch portion has a first element and a second element, the output of the first element is electrically connected to the input of the second element, and the output of the second element is the second element. It has a loop structure that is electrically connected to the input of one element. Further, the input of the first element is electrically connected to the wiring to which the input signal is given, and the output of the first element is electrically connected to the wiring to which the output signal is given. .. For example, an inverter can be used as the first element, and an inverter can be used as the second element. Further, for example, NAND can be used as the first element, and a clocked inverter can be used as the second element.</p><p>In the above, the other of the source electrode and the drain electrode of the transistor is electrically connected to the input of the first element of the latch portion. Further, the other of the source electrode and the drain electrode of the transistor is electrically connected to the wiring to which the input signal is given.</p><p>In the above, the transistor has a function of writing the data held in the latch portion to the capacitance of the data holding portion. Further, the transistor has a function of holding the written data in the capacitance of the data holding unit. Further, the transistor has a function of reading the data held in the capacitance of the data holding unit to the latch unit.</p><p>Another embodiment of the present invention includes a latch portion and a data holding portion for holding the data of the latch portion, and the data holding unit includes a first transistor, a second transistor, and a first capacitance. , Has a second capacity. The channel forming region of the first and second transistors has an oxide semiconductor layer. One of the source electrode and the drain electrode of the first transistor is electrically connected to one electrode of the first capacitance, and the other of the source electrode and the drain electrode of the first transistor is electrically connected to the latch portion. Has been done. One of the source electrode and the drain electrode of the second transistor is electrically connected to one electrode of the second capacitance, and the other of the source electrode and the drain electrode of the second transistor is electrically connected to the latch portion. Has been done. This constitutes a non-volatile latch circuit.</p><p>In the above, the latch portion has a first element and a second element, the output of the first element is electrically connected to the input of the second element, and the output of the second element is the second element. It has a loop structure that is electrically connected to the input of one element. Further, the input of the first element is electrically connected to the wiring to which the input signal is given, and the output of the first element is electrically connected to the wiring to which the output signal is given. .. For example, an inverter can be used as the first element, and an inverter can be used as the second element. Further, for example, NAND can be used as the first element, and a clocked inverter can be used as the second element.</p><p>In the above, the other of the source electrode and the drain electrode of the first transistor is electrically connected to the input of the first element of the latch portion. Further, the other of the source electrode and the drain electrode of the first transistor is electrically connected to the wiring to which the input signal is given. In the above, the other of the source electrode and the drain electrode of the second transistor is electrically connected to the output of the first element of the latch portion. Further, the other of the source electrode and the drain electrode of the second transistor is electrically connected to the wiring to which the output signal is given.</p><p>In the above, the first and second transistors have a function of writing the data held in the latch portion to the first and second capacitances of the data holding portion. Further, the first and second transistors have a function of holding the written data in the first and second capacitances of the data holding unit. Further, the first and second transistors have a function of reading the data held in the first and second capacitances of the data holding section to the latch section.</p><p>In the above, the transistor in which the oxide semiconductor layer formed of the oxide semiconductor material is used in the channel forming region has, for example, a channel width W of 1 × 10.⁴Even if the device is μm and the channel length (L) is 3 μm, the off current at room temperature is 1 × 10.^-13Below A, the subthreshold swing value (S value) is about 0.1 V / dec. (Gate insulating film thickness 100 nm). Further, the above-mentioned transistor has a transistor characteristic of normally off (in the case of the n-channel type, the threshold voltage becomes a positive value).</p><p>Therefore, the off-current, that is, the leakage current when the voltage between the gate and the source electrode is almost 0 is significantly smaller than that of the transistor using silicon. For example, the above W = 1 × 10⁴In a μm transistor, the leakage current at room temperature converted per 1 μm of channel width is 10 aAA or less (hereinafter, in this specification, the unit channel width leak current at room temperature is expressed as 10 aA / μm or less).</p><p>Therefore, by using a transistor using an oxide semiconductor layer in the channel formation region as a switching element, the charge accumulated in the capacity of the data holding unit is retained as it is even after the supply of the power supply voltage to the latch circuit is stopped. Can continue to do. That is, the data written in the data holding unit can be continuously held as it is.</p><p>For example, it is possible to have a much longer refresh time and retention than a DRAM having a transistor that uses silicon for the channel formation region, and it has the same level of memory retention (data retention) as non-volatile memory. ) Can have. Further, after the supply of the power supply voltage to the latch circuit is restarted, the data held in the data holding unit can be read out to the latch unit by using the transistor. As a result, it is possible to restore the logical state before the supply of the power supply voltage is stopped.</p><p>Further, in terms of temperature characteristics, it is possible to obtain a product in which the off-current is sufficiently low and the on-current is sufficiently high even at a high temperature. For example, V of a transistor using an oxide semiconductor layer in the channel formation region._G-I_DData have been obtained that the characteristics have little temperature dependence of on-current, mobility, and S value in the range of -25 ° C to 150 ° C. In addition, the off current is 1 × 10 in the above temperature range.^-13Very small data of A or less is obtained. One reason for this is that the oxide semiconductor used is one in which the hydrogen concentration is sufficiently reduced to be highly purified, the carrier concentration is sufficiently low, and the i-type or substantially i-type is used. it is conceivable that.</p><p>In this specification, the carrier concentration is 1 × 10.¹¹/cm³Less than "intrinsic" or "i-type" oxide semiconductors, and more, but 1x10¹²/cm³Those less than are called "substantially true" or "substantially type i".</p><p>As described above, one embodiment of the present invention provides a non-volatile latch circuit that has a wide temperature operating range, operates stably even at a high temperature, and does not erase the stored logical state even when the power is turned off.</p><p>In the above, various logic circuits can be provided by using the non-volatile latch circuit. Further, various semiconductor devices using the above logic circuit can be provided. For example, it is possible to stop the supply of the power supply voltage to one or a plurality of unused block circuits among the plurality of block circuits included in the logic circuit. By using the non-volatile latch circuit, the logical state of the block circuit can be continuously stored even after the supply of the power supply voltage to the block circuit is stopped. Further, the stored logical state can be read out after the supply of the power supply voltage to the block circuit is restarted. As a result, it is possible to restore the logical state before the supply of the power supply voltage is stopped.</p><p>In the above, as the oxide semiconductor layer, the quaternary metal oxide In-Sn-Ga-Zn-O system, the ternary metal oxide In-Ga-Zn-O system, and In-Sn- Zn-O series, In-Al-Zn-O series, Sn-Ga-Zn-O series, Al-Ga-Zn-O series, Sn-Al-Zn-O series, and binary metal oxides. In-Zn-O series, Sn-Zn-O series, Al-Zn-O series, Zn-Mg-O series, Sn-Mg-O series, In-Mg-O series, and unified metal oxides. It can be formed by using oxide semiconductors such as In-O type, Sn-O type, and Zn-O type. In addition, SiO is added to the oxide semiconductor.₂May be used.</p><p>In the present specification, for example, an In-Sn-Ga-Zn-O-based oxide semiconductor means an oxide semiconductor containing at least In, Sn, Ga, and Zn, and the composition ratio of each metal element. Is not limited, and may contain metal elements other than In, Sn, Ga, and Zn.</p><p>In addition, as an oxide semiconductor layer, InMO₃(ZnO)_mA thin film containing the material represented by (m&gt; 0) can be used. Here, M represents one or more metal elements selected from Ga, Al, Mn and Co. For example, as M, Ga, Ga and Al, Ga and Mn, Ga and Co and the like can be applied.</p><p>In the above, the hydrogen concentration of the oxide semiconductor layer is 5 × 10.¹⁹/cm³Below, preferably 5x10¹⁸/cm³Below, more preferably 5x10¹⁷/cm³Below, more preferably 1x10¹⁶/cm³Can be less than. The carrier concentration of the oxide semiconductor layer is 1 × 10.¹⁴/cm³Less than, preferably 1x10¹²/cm³Less than, more preferably 1x10¹¹/cm³Can be less than. The off-current of a transistor using such an i-type or substantially i-type oxide semiconductor is 1 × 10.^-17A or less, preferably 1 x 10^-18Can be A.</p><p>In the above, the transistor using the oxide semiconductor may be a bottom gate type or a top gate type. Further, it may be a bottom contact type or a top contact type. The bottom gate type transistor has at least a gate electrode on an insulating surface, a gate insulating film on the gate electrode, and an oxide semiconductor layer serving as a channel forming region on the gate insulating film that overlaps with the gate electrode.</p><p>The top gate type transistor has at least an oxide semiconductor layer serving as a channel forming region on the insulating surface, a gate insulating film on the oxide semiconductor layer, and a gate electrode overlapping the oxide semiconductor layer on the gate insulating film. Botomukon tact transistor includes an oxide semiconductor layer to be a channel formation region on the source electrode and the drain electrode. The top contact type transistor has a source electrode and a drain electrode on an oxide semiconductor layer serving as a channel forming region.</p><p>In this specification, terms such as "above" and "below" do not limit the positional relationship of the components to be "directly above" or "directly below". For example, the expression "gate electrode on the gate insulating layer" does not exclude those containing other components between the gate insulating layer and the gate electrode. In addition, the terms "upper" and "lower" are merely expressions used for convenience of explanation, and include those in which the upper and lower parts are interchanged unless otherwise specified.</p><p>Further, the terms "electrode" and "wiring" in the present specification do not functionally limit these components. For example, an "electrode" may be used as part of a "wiring" and vice versa. Further, the terms "electrode" and "wiring" also include the case where a plurality of "electrodes" and "wiring" are integrally formed.</p><p>Further, the functions of "source" and "drain" may be interchanged when transistors having different polarities are adopted or when the direction of current changes in circuit operation. Therefore, in the present specification, the terms "source" and "drain" may be used interchangeably.</p><p>Further, in the present specification, "electrically connected" includes a case where they are connected via "something having some kind of electrical action". Here, the "thing having some kind of electrical action" is not particularly limited as long as it enables the exchange of electric signals between the connection targets.</p><p>For example, "things having some kind of electrical action" include not only electrodes and wirings, but also switching elements such as transistors, resistance elements, inductors, capacitors, and other elements having various functions.</p><p>Further, generally, the "SOI substrate" refers to a substrate having a structure in which a silicon semiconductor layer is provided on an insulating surface, but in the present specification, a semiconductor layer made of a material other than silicon is provided on the insulating surface. It is used as a concept that also includes a substrate. That is, the semiconductor layer of the "SOI substrate" is not limited to the silicon semiconductor layer.</p><p>Further, the substrate in the "SOI substrate" is not limited to a semiconductor substrate such as a silicon wafer, but also includes a non-semiconductor substrate such as a glass substrate, a quartz substrate, a sapphire substrate, and a metal substrate. That is, those having a layer made of a semiconductor material on a conductor substrate or an insulator substrate are also widely included in the "SOI substrate".</p><p>Further, in the present specification, the term "semiconductor substrate" refers not only to a substrate made of only a semiconductor material but also to a whole substrate including a semiconductor material. That is, in the present specification and the like, the "SOI substrate" is also broadly included in the "semiconductor substrate".</p>

<p>According to one embodiment of the present invention, by using a transistor using an oxide semiconductor as a semiconductor material constituting a channel forming region as a switching element of a data holding unit, a transistor having a wide temperature operating range and stable operation even at a high temperature can be used. It is possible to realize a non-volatile latch circuit in which the stored logical state is not erased even when the power is turned off, or a latch circuit having a built-in data holding unit having a sufficiently long refresh period. Since data is written by switching transistors, there is virtually no limit to the number of rewrites. Further, the write voltage is about the threshold voltage of the transistor, and it is possible to operate at a low voltage. Further, since the electric charge accumulated in the capacity of the data holding unit is held as data as it is, the variation in the amount of electric charge held as data can be suppressed to be small as compared with the case where the residual polarization component is used as data. Can be easily read out.</p><p>By using the non-volatile latch circuit, various logic circuits can be realized. For example, in a logic circuit using a non-volatile latch circuit, power consumption can be reduced by turning off the power of unused blocks. In addition, since the logical state is memorized even when the power is turned off, it is possible to start the system when the power is turned on and shut down the system when the power is turned off at high speed and with low power consumption. Is.</p>

<figref num="1">The figure which shows an example of the structure of the non-volatile latch circuit.</figref><figref num="2">The figure which shows an example of the structure of a part of a non-volatile latch circuit.</figref><figref num="3">The figure which shows an example of the cross section of the element which a non-volatile latch circuit has.</figref><figref num="4">The figure which shows an example of the manufacturing method of the element which a non-volatile latch circuit has.</figref><figref num="5">The figure which shows an example of the manufacturing method of the element which a non-volatile latch circuit has.</figref><figref num="6">The figure which shows an example of the manufacturing method of the element which a non-volatile latch circuit has.</figref><figref num="7">The figure which shows an example of the cross-sectional structure of a transistor using an oxide semiconductor.</figref><figref num="8">The energy band diagram (schematic diagram) in the A-A'cross section of FIG.</figref><figref num="9">(A) Positive voltage (V) at the gate (GE1)_G&gt; 0) indicates a given state, (B) negative voltage (V) at gate (GE1)_GThe figure which shows the state which &lt;0) is given.</figref><figref num="10">Vacuum level and metal work function (φ_M), The figure which shows the relationship of electron affinity (χ) of an oxide semiconductor.</figref><figref num="11">The figure which shows the energy required for hot carrier injection in silicon (Si).</figref><figref num="12">The figure which shows the energy required for hot carrier injection in an oxide semiconductor (IGZO) of an In-Ga-Zn-O system.</figref><figref num="13">The figure which shows the energy required for hot carrier injection in silicon carbide (4H-SiC).</figref><figref num="14">The figure which shows the result of the device simulation about the short channel effect.</figref><figref num="15">The figure which shows the result of the device simulation about the short channel effect.</figref><figref num="16">The figure which shows an example of the cross section of the element which a non-volatile latch circuit has.</figref><figref num="17">The figure which shows an example of the manufacturing method of the element which a non-volatile latch circuit has.</figref><figref num="18">The figure which shows an example of the manufacturing method of the element which a non-volatile latch circuit has.</figref><figref num="19">The figure which shows an example of the structure and operation of the non-volatile latch circuit.</figref><figref num="20">The figure which shows an example of the operation of the non-volatile latch circuit.</figref><figref num="21">The figure which shows an example of the structure of the non-volatile latch circuit.</figref><figref num="22">The figure which shows an example of the structure of the non-volatile latch circuit.</figref><figref num="23">The figure which shows an example of the structure of the non-volatile latch circuit.</figref><figref num="24">The figure which shows an example of the operation of the non-volatile latch circuit.</figref><figref num="25">The figure which shows an example of the operation of the non-volatile latch circuit.</figref><figref num="26">The figure which shows an example of the structure of the non-volatile latch circuit.</figref><figref num="27">The figure which shows an example of the manufacturing method of the element which a non-volatile latch circuit has.</figref><figref num="28">The figure which shows an example of the manufacturing method of the element which a non-volatile latch circuit has.</figref><figref num="29">The figure which shows an example of the electronic device including the semiconductor device using the non-volatile latch circuit.</figref>

Embodiments of the present invention will be described below with reference to the drawings. However, the present invention is not limited to the following description. It is easily understood by those skilled in the art that the form and details of the present invention can be changed in various ways without departing from the spirit and scope thereof. Therefore, the present invention is not construed as being limited to the description of the embodiments shown below. In explaining the configuration of the present invention with reference to the drawings, reference numerals indicating the same objects are commonly used among different drawings.

The size, layer thickness, or region of each configuration shown in the drawings and the like of each embodiment may be exaggerated for the sake of clarity. Therefore, it is not necessarily limited to that scale.

The terms using ordinal numbers such as 1, 2, and 3 used in the present specification are added for convenience in order to identify the components, and the number is not limited.

(Embodiment 1) In the present embodiment, the configuration and operation of a non-volatile latch circuit, the configuration of an element included in the non-volatile latch circuit, a manufacturing method, and the like, which are one aspect of the disclosed invention, are described in FIGS. 2, FIGS. 3, 4 to 6, 7 to 10, and 11 to 15 will be described.

&lt;Configuration and Operation of Non-Volatile Latch Circuit&gt; FIG. 1 shows the configuration of a non-volatile latch circuit 400 having a latch unit 411 and a data holding unit 401 for holding data of the latch unit.

In the non-volatile latch circuit 400 shown in FIG. 1, the output of the first element (D1) 412 is electrically connected to the input of the second element (D2) 413, and the output of the second element (D2) 413 is connected. Has a latch portion 411 having a loop structure electrically connected to the input of the first element (D1) 412, and a data holding portion 401 for holding the data of the latch portion.

The input of the first element (D1) 412 is electrically connected to the wiring 414 to which the input signal of the latch circuit is given. The output of the first element (D1) 412 is electrically connected to the wiring 415 to which the output signal of the latch circuit is given.

When there are multiple inputs of the first element (D1) 412, one of them can be electrically connected to the wiring 414 to which the input signal of the latch circuit is given. If there are multiple inputs for the second element (D2) 413, one of them can be electrically connected to the output of the first element (D1) 412.

As the first element (D1) 412, an element in which the input signal is inverted and the output is used can be used. For example, an inverter, NAND, NOR, clocked inverter, or the like can be used for the first element (D1) 412. Further, as the second element (D2) 413, an element in which the input signal is inverted and the output is used can be used. For example, an inverter, NAND, NOR, clocked inverter, or the like can be used for the second element (D2) 413.

The data holding unit 401 uses a transistor 402 that uses an oxide semiconductor as a semiconductor material constituting the channel forming region as a switching element. Further, it has a capacitance 404 electrically connected to the source electrode or the drain electrode of the transistor 402. That is, one of the electrodes having a capacitance of 404 is electrically connected to one of the source electrode and the drain electrode of the transistor 402. The other of the source electrode and the drain electrode of the transistor 402 is electrically connected to the wiring to which the input signal of the first element and the input signal of the latch circuit are given. The potential Vc is given to the other end of the electrode with a capacitance of 404.

Further, the data holding unit 401 can have the configurations shown in FIGS. 2 (A) and 2 (B) instead of the configurations shown in FIG.

In the data holding unit 401 shown in FIG. 2A, the transistor 402 has a first gate electrode and a second gate electrode. The second gate electrode is provided on the opposite side of the first gate electrode with the oxide semiconductor layer forming the channel forming region in between. The first gate electrode is electrically connected to the wiring to which the control signal is given. The second gate electrode is electrically connected to a wiring to which a predetermined potential is applied. For example, the second gate electrode is electrically connected to a wire that is given a negative potential or ground potential (GND).

Further, in the data holding unit 401 shown in FIG. 2A, one of the electrodes having a capacity of 404 is electrically connected to one of the source electrode and the drain electrode of the transistor 402. The other of the source electrode and the drain electrode of the transistor 402 is electrically connected to the wiring to which the input signal of the first element and the input signal of the latch circuit are given. The potential Vc is given to the other end of the electrode with a capacitance of 404.

In the non-volatile latch circuit using the data holding unit 401 shown in FIG. 2 (A), in addition to the effect of the non-volatile latch circuit shown in FIG. 1, the electrical characteristics of the transistor 402 (for example, the threshold voltage) ) Can be easily adjusted. For example, by applying a negative potential to the second gate electrode of the transistor 402, the transistor 402 can be easily turned off normally.

In the data holding unit 401 shown in FIG. 2B, the transistor 402 has a first gate electrode and a second gate electrode. The second gate electrode is provided on the opposite side of the first gate electrode with the oxide semiconductor layer forming the channel forming region in between. The second gate electrode is electrically connected to the first gate electrode. Further, in the data holding unit 401 shown in FIG. 2B, one of the electrodes having a capacity of 404 is electrically connected to one of the source electrode and the drain electrode of the transistor 402. The other of the source electrode and the drain electrode of the transistor 402 is electrically connected to the wiring to which the input signal of the first element and the input signal of the latch circuit are given. The potential Vc is given to the other end of the electrode with a capacitance of 404. In the non-volatile latch circuit using the data holding unit 401 shown in FIG. 2 (B), in addition to the effect of the non-volatile latch circuit shown in FIG. 1, the effect of increasing the amount of current of the transistor 402 can be obtained.

In the non-volatile latch circuit having the configurations shown in FIGS. 1 and 2, information can be written, held, and read as follows. In the following, the description will be based on the configuration shown in FIG. 1, but the same applies to other configurations.

The transistor 402 using this oxide semiconductor has a function of writing the data held in the latch unit 411 to the capacity 404 of the data holding unit 401. Further, the transistor 402 has a function of holding the data written in the capacity 404 of the data holding unit 401. Further, the transistor 402 has a function of reading the data held in the capacity 404 of the data holding unit 401 to the latch unit 411.

The operation of writing and holding the data held in the latch unit 411 to the data holding unit 401, reading the data from the data holding unit 401 to the latch unit 411, and rewriting the data of the data holding unit 401 will be described. First, a potential for turning on the transistor 402 is supplied to the gate electrode of the transistor 402 to turn on the transistor 402. As a result, the data held in the latch portion, that is, the potential of the input of the first element (D1) 412 held in the latch portion is given to one electrode of the capacitance 404. As a result, on one electrode of the capacitance 404, an electric charge corresponding to the input potential of the first element (D1) 412 held in the latch portion is accumulated (writing).

After that, the potential of the gate electrode of the transistor 402 is set to the potential at which the transistor 402 is turned off, and the transistor 402 is turned off, so that the charge accumulated in one electrode of the capacitance 404 is retained (retained). Further, after the input potential of the first element (D1) 412 is set to the floating state, the potential for turning on the transistor 402 is supplied to the gate electrode of the transistor 402, and the transistor 402 is turned on to obtain the capacitance. Charges are distributed between one electrode of the 404 and the input of the first element (D1) 412. As a result, the input of the first element (D1) 412 is given a potential corresponding to the electric charge accumulated in the potential of one electrode of the capacitance 404. Then, the data is held in the latch portion. As a result, data can be read (read). The data can be rewritten in the same manner as the above-mentioned data writing and holding.

The oxide semiconductor layer of the transistor 402 is an In-Sn-Ga-Zn-O system which is a quaternary metal oxide, an In-Ga-Zn-O system which is a ternary metal oxide, and an In-Sn. -Zn-O series, In-Al-Zn-O series, Sn-Ga-Zn-O series, Al-Ga-Zn-O series, Sn-Al-Zn-O series, and binary metal oxides With certain In-Zn-O series, Sn-Zn-O series, Al-Zn-O series, Zn-Mg-O series, Sn-Mg-O series, In-Mg-O series, and unitary metal oxides It can be formed by using certain oxide semiconductors such as In-O system, Sn-O system, and Zn-O system. In addition, SiO is added to the oxide semiconductor.₂May be used.

In addition, as an oxide semiconductor layer, InMO₃(ZnO)_mA thin film containing the material represented by (m&gt; 0) can be used. Here, M represents one or more metal elements selected from Ga, Al, Mn and Co. For example, as M, Ga, Ga and Al, Ga and Mn, Ga and Co and the like can be applied.

It is desirable that the oxide semiconductor layer is one in which impurities such as hydrogen are sufficiently removed, oxygen is supplied, and the purity is high. Specifically, the hydrogen concentration of the oxide semiconductor layer measured by secondary ion mass spectrometry (SIMS) is 5 × 10.¹⁹/cm³Below, preferably 5x10¹⁸/cm³Below, more preferably 5x10¹⁷/cm³Below, more preferably 1x10¹⁶/cm³Try to be less than.

The carrier concentration of the oxide semiconductor layer is 1 × 10.¹⁴/cm³Less than, preferably 1x10¹²/cm³Less than, more preferably 1x10¹¹/cm³Can be less than. Further, in the oxide semiconductor layer in which the hydrogen concentration is sufficiently reduced to supply oxygen and the oxide semiconductor layer is highly purified, carriers in a general silicon wafer (a silicon wafer to which a small amount of impurity elements such as phosphorus and boron are added) are used. Concentration (1 x 10¹⁴/cm³A sufficiently low carrier concentration value (eg, 1x10) compared to the degree)¹²/cm³Less than, preferably 1x10¹¹/cm³Less than).

In this way, by using an i-type or substantially i-type oxide semiconductor in which the hydrogen concentration is sufficiently reduced to be highly purified and the carrier concentration is sufficiently low, extremely excellent off-current characteristics are obtained. Transistor 402 can be obtained. For example, the channel width W is 1 × 10.⁴Even if the device is μm and the channel length L is 3 μm, the drain voltage V applied to the drain electrode_DIs + 1V or + 10V, and the gate voltage V applied to the gate electrode_GIn the range of -5V to -20V, the off-current at room temperature is 1x10.^-13A or less. Further, the above-mentioned transistor has a normally-off transistor characteristic. Therefore, the off-current, that is, the leakage current when the voltage between the gate and the source electrode is almost 0 is significantly smaller than that of the transistor using silicon. For example, the unit channel width leakage current at room temperature is 10 aA / μm or less.

Further, in terms of temperature characteristics, it is possible to obtain a product in which the off-current is sufficiently low and the on-current is sufficiently high even at a high temperature. For example, V of transistor 402_G-I_DData have been obtained that the characteristics have little temperature dependence of on-current, mobility, and S value in the range of -25 ° C to 150 ° C. In addition, the off current is 1 × 10 in the above temperature range.^-13Very small data is obtained, which is A or less (measurement limit or less). One reason for this is that the oxide semiconductor used is one in which the hydrogen concentration is sufficiently reduced to be highly purified, the carrier concentration is sufficiently low, and the i-type or substantially i-type is used. it is conceivable that.

In this way, the transistor 402 using an i-type or substantially i-type oxide semiconductor in which the hydrogen concentration is sufficiently reduced to be highly purified and the carrier concentration is sufficiently low is used as the switching element. Therefore, even after the supply of the power supply voltage to the latch circuit 400 is stopped, the electric charge accumulated in the capacity 404 of the data holding unit 401 can be continuously held for an extremely long time. That is, the data written in the data holding unit 401 can be held for an extremely long time.

For example, it is possible to have a much longer refresh time and retention than a DRAM having a transistor that uses silicon for the channel formation region, and it has the same level of memory retention (data retention) as non-volatile memory. ) Can have. Further, by reading the data held in the data holding unit 401, it is possible to restore the logical state before the power supply voltage supply is stopped. In this way, the transistor 402 using an i-type or substantially i-type oxide semiconductor in which the hydrogen concentration is sufficiently reduced to be highly purified and the carrier concentration is sufficiently low is used as the switching element. Therefore, it is possible to realize a new non-volatile latch circuit that has a wide temperature operating range, operates stably even at high temperatures, and does not erase the stored logical state even when the power is turned off.

&lt;Structure of elements included in the non-volatile latch circuit&gt; Among the elements included in the non-volatile latch circuit 400, the elements other than the transistor 402 using the oxide semiconductor may use a material other than the oxide semiconductor as the semiconductor material. it can. As a material other than the oxide semiconductor, single crystal silicon, crystalline silicon and the like can be used. For example, elements other than the transistor 402 can be provided on a substrate containing a semiconductor material. As the substrate containing the semiconductor material, a silicon wafer, an SOI (Silicon on Insulator) substrate, a silicon film on an insulating surface, or the like can be used. High-speed operation is possible by using a material other than an oxide semiconductor. For example, the first element (D1) 412 and the second element (D2) 413 of the latch portion can be formed by a transistor using a material other than an oxide semiconductor.

FIG. 3 is a cross-sectional view showing an example of the configuration of the element included in the non-volatile latch circuit. FIG. 3A shows a transistor 160 using a material other than an oxide semiconductor at the lower part and a transistor 402 using an oxide semiconductor at the upper part. The transistor 160 using a material other than the oxide semiconductor can be used as a transistor constituting the first element (D1) 412 and the second element (D2) 413 included in the latch portion. Other elements of the non-volatile latch circuit may have the same or similar configuration as the transistor 160.

Further, an element such as a capacitance 404 included in the non-volatile latch circuit can be formed by using a conductive film, a semiconductor film, an insulating film, or the like constituting the transistor 402 or the transistor 160. Although the transistor 160 and the transistor 402 are both described as n-type transistors, a p-type transistor may be adopted. The transistor 160 can be easily made into a p-type. Further, FIG. 3B is an example in which the connection relationship between the transistor 402 and the lower electrode (or wiring) is different from that in FIG. 3A. In the following, the configuration of FIG. 3 (A) will be mainly described.

The transistor 160 includes a channel forming region 116 provided on a substrate 100 containing a semiconductor material, an impurity region 114 provided so as to sandwich the channel forming region 116, and a high-concentration impurity region 120 (these are also simply referred to as an impurity region). ), The gate insulating layer 108a provided on the channel forming region 116, the gate electrode 110a provided on the gate insulating layer 108a, the source electrode or drain electrode 130a electrically connected to the impurity region 114, and It has a source electrode or a drain electrode 130b (see FIG. 3 (A)).

Here, a sidewall insulating layer 118 is provided on the side surface of the gate electrode 110a. Further, the region of the substrate 100 that does not overlap with the sidewall insulating layer 118 when viewed in a plane has a high-concentration impurity region 120 and a metal compound region 124 in contact with the high-concentration impurity region 120. Further, an element separation insulating layer 106 is provided on the substrate 100 so as to surround the transistor 160, and an interlayer insulating layer 126 and an interlayer insulating layer 128 are provided so as to cover the transistor 160.

The source electrode or drain electrode 130a and the source electrode or drain electrode 130b are electrically connected to the metal compound region 124 through openings formed in the interlayer insulating layer 126 and the interlayer insulating layer 128. That is, the source electrode or drain electrode 130a and the source electrode or drain electrode 130b are electrically connected to the high-concentration impurity region 120 and the impurity region 114 via the metal compound region 124.

The transistor 402 includes a gate electrode 136d provided on the interlayer insulating layer 128, a gate insulating layer 138 provided on the gate electrode 136d, an oxide semiconductor layer 140 provided on the gate insulating layer 138, and an oxide. It has a source electrode or drain electrode 142a and a source electrode or drain electrode 142b provided on the semiconductor layer 140 and electrically connected to the oxide semiconductor layer 140 (see FIG. 3 (A)).

Further, a protective insulating layer 144 is provided on the transistor 402 so as to be in contact with a part of the oxide semiconductor layer 140, and an interlayer insulating layer 146 is provided on the protective insulating layer 144. Here, the protective insulating layer 144 and the interlayer insulating layer 146 are provided with openings that reach the source electrode or drain electrode 142a and the source electrode or drain electrode 142b, and the electrodes 150d and 150e are sourced through the openings. It is formed in contact with the electrode or drain electrode 142a and the source electrode or drain electrode 142b.

Further, at the same time as the formation of the electrodes 150d and 150e, the electrodes 150a, 150b, and electrodes in contact with the electrodes 136a, 136b, and 136c are passed through the openings provided in the gate insulating layer 138, the protective insulating layer 144, and the interlayer insulating layer 146. 150c is formed. Although an example of a bottom gate type transistor is shown as the transistor 402, the present invention is not limited to this. It may be a top gate type transistor.

Here, it is desirable that the oxide semiconductor layer 140 is one in which impurities such as hydrogen are sufficiently removed, oxygen is supplied, and the purity is high. Specifically, the hydrogen concentration of the oxide semiconductor layer 140 measured by secondary ion mass spectrometry (SIMS) is 5 × 10.¹⁹/cm³Below, preferably 5x10¹⁸/cm³Below, more preferably 5x10¹⁷/cm³Below, more preferably 1x10¹⁶/cm³Try to be less than.

The oxide semiconductor layer 140 in which the hydrogen concentration is sufficiently reduced, oxygen is supplied, and the purity is high is found in a general silicon wafer (a silicon wafer to which a small amount of impurity elements such as phosphorus and boron are added). Carrier concentration (1 x 10)¹⁴/cm³A sufficiently low carrier concentration value (eg, 1x10) compared to the degree)¹²/cm³Less than, preferably 1x10¹¹/cm³Less than).

As described above, by using an i-shaped or substantially i-shaped oxide semiconductor, a transistor 402 having extremely excellent off-current characteristics can be obtained. For example, drain voltage V_DIs + 1V or + 10V and the gate voltage V_GIn the range of -5V to -20V, the off-current at room temperature is 1x10.^-13A or less. Further, the above-mentioned transistor has a normally-off transistor characteristic. Therefore, the off-current, that is, the leakage current when the voltage between the gate and the source electrode is almost 0 is significantly smaller than that of the transistor using silicon. For example, the unit channel width leakage current at room temperature is 10 aA / μm or less.

Further, in terms of temperature characteristics, it is possible to obtain a product in which the off-current is sufficiently low and the on-current is sufficiently high even at a high temperature. For example, V of transistor 402_G-I_DData have been obtained that the characteristics have little temperature dependence of on-current, mobility, and S value in the range of -25 ° C to 150 ° C. In addition, the off current is 1 × 10 in the above temperature range.^-13Very small data of A is obtained. One reason for this is that the oxide semiconductor used is one in which the hydrogen concentration is sufficiently reduced to be highly purified, the carrier concentration is sufficiently low, and the i-type or substantially i-type is used. it is conceivable that.

As described above, by applying the oxide semiconductor layer 140 whose hydrogen concentration is sufficiently reduced and purified, and reducing the off-current of the transistor 402, a semiconductor device having a new configuration can be realized.

Further, an insulating layer 152 is provided on the interlayer insulating layer 146, and electrodes 154a, 154b, electrodes 154c, and electrodes 154d are provided so as to be embedded in the insulating layer 152. Here, the electrode 154a is in contact with the electrode 150a, the electrode 154b is in contact with the electrode 150b, the electrode 154c is in contact with the electrode 150c and the electrode 150d, and the electrode 154d is in contact with the electrode 150e.

That is, the source electrode or drain electrode 142a of the transistor 402 is electrically connected to other elements (such as a transistor using a material other than an oxide semiconductor) via the electrode 130c, the electrode 136c, the electrode 150c, the electrode 154c, and the electrode 150d. It is connected to (see Fig. 3 (A)). Further, the source electrode or drain electrode 142b of the transistor 402 is electrically connected to other elements via the electrode 150e and the electrode 154d. The configuration of the electrodes (electrode 130c, electrode 136c, electrode 150c, electrode 154c, electrode 150d, etc.) related to the connection is not limited to the above, and can be added or omitted as appropriate.

FIG. 3B shows a case where the source electrode or drain electrode 142a of the transistor 402 has a connection relationship different from that in FIG. 3A. Specifically, the source electrode or the drain electrode 142a is electrically connected to the electrode 110b via the electrode 130c, the electrode 136c, the electrode 150c, the electrode 154c, and the electrode 150d. Here, the electrode 110b is formed in the same manner as the gate electrode 110a. The electrode 110b may be a component of a transistor or a part of wiring or the like. The configuration of the electrodes (electrode 130c, electrode 136c, electrode 150c, electrode 154c, electrode 150d, etc.) related to the connection is not limited to the above, and can be added or omitted as appropriate.

In the above, two examples relating to typical connection relationships have been shown, but one aspect of the disclosed invention is not limited to this. For example, the configuration shown in FIG. 3 (A) and the configuration shown in FIG. 3 (B) may be included together. Further, the gate electrode 110a of the transistor 160 and the source electrode or drain electrode 142a of the transistor 402 may be electrically connected.

&lt;Method of manufacturing the element of the non-volatile latch circuit&gt; Next, an example of the method of manufacturing the element of the non-volatile latch circuit will be described. In the following, a method for manufacturing the transistor 160 will be described first with reference to FIG. 4, and then a method for manufacturing the transistor 402 will be described with reference to FIG. 5 or FIG. The element included in the non-volatile latch circuit can be manufactured by the manufacturing method shown below. Note that FIG. 4 shows only the cross section corresponding to A1-A2 in FIG. 3 (A). Further, FIG. 5 or FIG. 6 shows a cross section corresponding to A1-A2 and B1-B2 in FIG. 3 (A).

&lt;Method of manufacturing the lower transistor&gt; First, a substrate 100 containing a semiconductor material is prepared (see FIG. 4 (A)). As the substrate 100 containing the semiconductor material, a single crystal semiconductor substrate such as silicon or silicon carbide, a polycrystalline semiconductor substrate, a compound semiconductor substrate such as silicon germanium, an SOI substrate, or the like can be applied. Here, an example in which a single crystal silicon substrate is used as the substrate 100 containing a semiconductor material will be shown.

In general, the "SOI substrate" refers to a substrate having a structure in which a silicon semiconductor layer is provided on an insulating surface, but in the present specification, a structure in which a semiconductor layer made of a material other than silicon is provided on the insulating surface. It is used as a concept including the substrate of. That is, the semiconductor layer of the "SOI substrate" is not limited to the silicon semiconductor layer. Further, the SOI substrate shall include one having a semiconductor layer provided on an insulating substrate such as a glass substrate.

A protective layer 102 serving as a mask for forming the element separation insulating layer is formed on the substrate 100 (see FIG. 4 (A)). As the protective layer 102, for example, an insulating layer made of a material such as silicon oxide, silicon nitride, or silicon nitride can be used. Before and after this step, in order to control the threshold voltage of the transistor, an impurity element that imparts n-type conductivity or an impurity element that imparts p-type conductivity may be added to the substrate 100. .. When the semiconductor is silicon, for example, phosphorus or arsenic can be used as the impurity that imparts n-type conductivity. Further, as the impurity imparting p-type conductivity, for example, boron, aluminum, gallium and the like can be used.

Next, etching is performed using the protective layer 102 as a mask to remove a part of the substrate 100 in the region not covered by the protective layer 102 (exposed region). As a result, the separated semiconductor region 104 is formed (see FIG. 4 (B)). Dry etching is preferably used for the etching, but wet etching may be used. The etching gas and the etching solution can be appropriately selected according to the material to be etched.

Next, an insulating layer is formed so as to cover the semiconductor region 104, and the insulating layer in the region overlapping the semiconductor region 104 is selectively removed to form the element separation insulating layer 106 (see FIG. 4 (B)). ). The insulating layer is formed by using silicon oxide, silicon nitride, silicon nitride or the like. As a method for removing the insulating layer, there are polishing treatment such as CMP and etching treatment, and any of them may be used. The protective layer 102 is removed after the semiconductor region 104 is formed or the element separation insulating layer 106 is formed.

Next, an insulating layer is formed on the semiconductor region 104, and a layer containing a conductive material is formed on the insulating layer.

The insulating layer will be the gate insulating layer later, and is a single layer of a film containing silicon oxide, silicon nitride, silicon nitride, hafnium oxide, aluminum oxide, tantalum oxide, etc. obtained by using the CVD method, sputtering method, or the like. It may be a structure or a laminated structure. Alternatively, the insulating layer may be formed by oxidizing and nitriding the surface of the semiconductor region 104 by high-density plasma treatment or thermal oxidation treatment. The high-density plasma treatment can be performed using, for example, a rare gas such as He, Ar, Kr, or Xe, or a mixed gas such as oxygen, nitrogen oxide, ammonia, nitrogen, or hydrogen. The thickness of the insulating layer is not particularly limited, but may be, for example, 1 nm or more and 100 nm or less.

The layer containing the conductive material can be formed by using a metal material such as aluminum, copper, titanium, tantalum, or tungsten. Further, a semiconductor material such as polycrystalline silicon containing an impurity element that imparts conductivity may be used to form a layer containing the conductive material. The forming method is not particularly limited, and various film forming methods such as a vapor deposition method, a CVD method, a sputtering method, and a spin coating method can be used. In this embodiment, an example of forming a layer containing a conductive material using a metal material will be shown.

Then, the insulating layer and the layer containing the conductive material are selectively etched to form the gate insulating layer 108a and the gate electrode 110a (see FIG. 4C).

Next, an insulating layer 112 covering the gate electrode 110a is formed (see FIG. 4 (C)). Then, phosphorus (P), arsenic (As), or the like is added to the semiconductor region 104 to form an impurity region 114 having a shallow bonding depth (see FIG. 4 (C)). Here, phosphorus and arsenic are added to form an n-type transistor, but when forming a p-type transistor, impurity elements such as boron (B) and aluminum (Al) may be added. ..

By forming the impurity region 114, a channel forming region 116 is formed in the lower part of the gate insulating layer 108a of the semiconductor region 104 (see FIG. 4 (C)). Here, the concentration of impurities to be added can be appropriately set, but when the semiconductor element is highly miniaturized, it is desirable to increase the concentration. Further, although the step of forming the impurity region 114 after forming the insulating layer 112 is adopted here, it may be a step of forming the insulating layer 112 after forming the impurity region 114.

Next, the sidewall insulating layer 118 is formed (see FIG. 4 (D)). The sidewall insulating layer 118 can be formed in a self-aligned manner by forming an insulating layer so as to cover the insulating layer 112 and then applying a highly anisotropic etching treatment to the insulating layer. At this time, it is preferable to partially etch the insulating layer 112 to expose the upper surface of the gate electrode 110a and the upper surface of the impurity region 114.

Next, an insulating layer is formed so as to cover the gate electrode 110a, the impurity region 114, the sidewall insulating layer 118, and the like. Then, phosphorus (P), arsenic (As), or the like is added to the region where the insulating layer is in contact with the impurity region 114 to form the high-concentration impurity region 120. After that, the insulating layer is removed, and a metal layer 122 is formed so as to cover the gate electrode 110a, the sidewall insulating layer 118, the high-concentration impurity region 120, and the like (see FIG. 4 (E)).

The metal layer 122 can be formed by using various film forming methods such as a vacuum vapor deposition method, a sputtering method, and a spin coating method. It is desirable that the metal layer 122 is formed by using a metal material that reacts with the semiconductor material constituting the semiconductor region 104 to form a metal compound having low resistance. Examples of such metal materials include titanium, tantalum, tungsten, nickel, cobalt, platinum and the like.

Next, heat treatment is performed to react the metal layer 122 with the semiconductor material. As a result, the metal compound region 124 in contact with the high-concentration impurity region 120 is formed (see FIG. 4 (F)). When polycrystalline silicon or the like is used as the gate electrode 110a, a metal compound region is also formed in the portion of the gate electrode 110a in contact with the metal layer 122.

As the heat treatment, for example, a heat treatment by irradiation with a flash lamp can be used. Of course, other heat treatment methods may be used, but in order to improve the controllability of the chemical reaction related to the formation of the metal compound, it is desirable to use a method that can realize the heat treatment in a very short time. The above-mentioned metal compound region is formed by the reaction between the metal material and the semiconductor material, and is a region in which the conductivity is sufficiently enhanced. By forming the metal compound region, the electric resistance can be sufficiently reduced and the element characteristics can be improved. After forming the metal compound region 124, the metal layer 122 is removed.

Next, the interlayer insulating layer 126 and the interlayer insulating layer 128 are formed so as to cover each of the configurations formed by the above steps (see FIG. 4 (G)). The interlayer insulating layer 126 and the interlayer insulating layer 128 can be formed by using a material containing an inorganic insulating material such as silicon oxide, silicon nitride oxide, silicon nitride, hafnium oxide, aluminum oxide, and tantalum oxide. It can also be formed using an organic insulating material such as polyimide or acrylic. Here, the structure is a two-layer structure of the interlayer insulating layer 126 and the interlayer insulating layer 128, but the configuration of the interlayer insulating layer is not limited to this. After the interlayer insulating layer 128 is formed, it is desirable to flatten the surface thereof by CMP or etching treatment.

Then, an opening reaching the metal compound region 124 is formed in the interlayer insulating layer, and a source electrode or drain electrode 130a and a source electrode or drain electrode 130b are formed in the opening (see FIG. 4 (H)). For the source electrode or drain electrode 130a and the source electrode or drain electrode 130b, for example, after forming a conductive layer in a region including an opening by using a PVD method or a CVD method, the above-mentioned conductivity is formed by using a method such as etching treatment or CMP. It can be formed by removing part of the layer.

When the source electrode or drain electrode 130a or the source electrode or drain electrode 130b is formed by removing a part of the conductive layer, it is desirable to process the surface so that the surface becomes flat. For example, when a titanium film or a titanium nitride film is thinly formed in a region including an opening and then a tungsten film is formed so as to be embedded in the opening, unnecessary tungsten, titanium, titanium nitride, etc. are removed by the subsequent CMP. At the same time, the flatness of the surface can be improved. By flattening the surface including the source electrode or drain electrode 130a and the source electrode or drain electrode 130b in this way, it is possible to form a good electrode, wiring, insulating layer, semiconductor layer, etc. in a later step. It becomes.

The material that can be used as the source electrode or drain electrode 130a and the source electrode or drain electrode 130b is not particularly limited, and various conductive materials can be used. For example, conductive materials such as molybdenum, titanium, chromium, tantalum, tungsten, aluminum, copper, neodymium and scandium can be used. Further, although only the source electrode or drain electrode 130a and the source electrode or drain electrode 130b that come into contact with the metal compound region 124 are shown here, the electrode 130c and the like in FIG. 3 can also be formed in this step. ..

Specifically, for example, a method of forming a thin titanium film by the PVD method in a region including an opening, forming a thin titanium nitride film by the CVD method, and then forming a tungsten film so as to be embedded in the opening can be applied. it can. Here, the titanium film formed by the PVD method has a function of reducing the oxide film that can be formed on the surface of the metal compound region and reducing the contact resistance with the metal compound region. Further, the titanium nitride film formed thereafter has a barrier function of suppressing the diffusion of the conductive material. Further, after forming a barrier film made of titanium, titanium nitride or the like, a copper film may be formed by a plating method. The dual damascene method may be applied as well as the so-called single damascene method.

As described above, the transistor 160 using the substrate 100 containing the semiconductor material is formed. After the above steps, electrodes, wiring, an insulating layer and the like may be further formed. By adopting a multi-layer wiring structure having a laminated structure of an interlayer insulating layer and a conductive layer as a wiring structure, a highly integrated semiconductor device can be provided.

&lt;Method of manufacturing the upper transistor&gt; Next, the process of manufacturing the transistor 402 on the interlayer insulating layer 128 will be described with reference to FIGS. 5 and 6. Since FIGS. 5 and 6 show various electrodes on the interlayer insulating layer 128 and the manufacturing process of the transistor 402 and the like, the transistor 160 and the like existing below the transistor 402 are omitted.

First, the insulating layer 132 is formed on the interlayer insulating layer 128, the source electrode or drain electrode 130a, the source electrode or drain electrode 130b, and the electrode 130c (see FIG. 5 (A)). Then, an opening is formed in the insulating layer 132 to reach the source electrode or drain electrode 130a, the source electrode or drain electrode 130b, and the electrode 130c. Then, the conductive layer 134 is formed so as to be embedded in the opening (see FIG. 5 (B)). After that, a part of the conductive layer 134 is removed by a method such as etching treatment or CMP to expose the insulating layer 132 to form the electrode 136a, the electrode 136b, the electrode 136c, and the gate electrode 136d (FIG. 5 (C). )reference).

The insulating layer 132 can be formed by using a PVD method, a CVD method, or the like. Further, it can be formed by using a material containing an inorganic insulating material such as silicon oxide, silicon nitride oxide, silicon nitride, hafnium oxide, aluminum oxide, and tantalum oxide.

The opening of the insulating layer 132 can be formed by a method such as etching using a mask. The mask can be formed by a method such as exposure using a photomask. Either wet etching or dry etching may be used as the etching, but from the viewpoint of microfabrication, it is preferable to use dry etching.

The conductive layer 134 can be formed by using a film forming method such as a PVD method or a CVD method. Examples of the material that can be used for forming the conductive layer include conductive materials such as molybdenum, titanium, chromium, tantalum, tungsten, aluminum, copper, neodymium, and scandium, and alloys and compounds (for example, nitrides) thereof. (See Figure 5 (B)).

More specifically, for example, a method of forming a thin titanium film by the PVD method in a region including an opening, forming a thin titanium nitride film by the CVD method, and then forming a tungsten film so as to be embedded in the opening is applied. Can be done. Here, the titanium film formed by the PVD method reduces the oxide film that can be formed on the surface of the lower electrode (here, source electrode or drain electrode 130a, source electrode or drain electrode 130b, electrode 130c, etc.) and lower electrode. It has a function of reducing contact resistance with.

Further, the titanium nitride film formed thereafter has a barrier function of suppressing the diffusion of the conductive material. Further, after forming a barrier film made of titanium, titanium nitride or the like, a copper film may be formed by a plating method. Not limited to the so-called single damascene method, a dual damascene method or the like may be applied.

After forming the conductive layer 134, a part of the conductive layer 134 is removed by a method such as etching treatment or CMP to expose the insulating layer 132 to form electrodes 136a, 136b, 136c, and gate electrodes 136d. Can be done (see Figure 5 (C)). When the electrode 136a, the electrode 136b, the electrode 136c, and the gate electrode 136d are formed by removing a part of the conductive layer 134, it is desirable to process the surface so that the surface becomes flat. By flattening the surfaces of the insulating layer 132, the electrode 136a, the electrode 136b, the electrode 136c, and the gate electrode 136d in this way, a good electrode, wiring, insulating layer, semiconductor layer, etc. can be formed in a later step. Is possible.

Next, the gate insulating layer 138 is formed so as to cover the insulating layer 132, the electrode 136a, the electrode 136b, the electrode 136c, and the gate electrode 136d (see FIG. 5 (D)). The gate insulating layer 138 can be formed by using a CVD method, a sputtering method, or the like. Further, the gate insulating layer 138 is preferably formed so as to contain silicon oxide, silicon nitride, silicon oxide, silicon nitride oxide, aluminum oxide, hafnium oxide, tantalum oxide and the like. The gate insulating layer 138 may have a single-layer structure or a laminated structure.

For example, as a raw material gas, silane (SiH)₄), The gate insulating layer 138 made of silicon oxide can be formed by the plasma CVD method using oxygen and nitrogen. The thickness of the gate insulating layer 138 is not particularly limited, but may be, for example, 10 nm or more and 500 nm or less. In the case of a laminated structure, for example, it is preferable to laminate a first gate insulating layer having a film thickness of 50 nm or more and 200 nm or less and a second gate insulating layer having a film thickness of 5 nm or more and 300 nm or less on the first gate insulating layer. is there.

If the gate insulating layer 138 contains hydrogen, water, or the like, hydrogen may invade the oxide semiconductor layer or oxygen may be extracted from the oxide semiconductor layer by hydrogen, which may deteriorate the characteristics of the transistor. is there. Therefore, it is desirable that the gate insulating layer 138 is formed so as not to contain hydrogen or water as much as possible.

For example, when a sputtering method or the like is used, it is desirable to form the gate insulating layer 138 in a state where the moisture in the processing chamber is removed. Further, in order to remove water in the treatment chamber, it is desirable to use an adsorption type vacuum pump such as a cryopump, an ion pump, or a titanium sublimation pump. A turbo pump with a cold trap added may be used. Since hydrogen, water, and the like are sufficiently removed from the treatment chamber exhausted by using a cryopump or the like, the concentration of impurities contained in the gate insulating layer 138 can be reduced.

Further, when forming the gate insulating layer 138, it is desirable to use a high-purity gas in which impurities such as hydrogen and water are reduced to several ppm or less (preferably several ppb or less).

It should be noted that an oxide semiconductor (highly purified oxide semiconductor) that has been i-shaped or substantially i-shaped by removing impurities is extremely sensitive to interface states and interfacial charges. When such an oxide semiconductor is used for the oxide semiconductor layer, the interface with the gate insulating layer is important. That is, the gate insulating layer 138 in contact with the highly purified oxide semiconductor layer is required to have high quality.

For example, the high-density plasma CVD method using a μ wave (frequency 2.45 GHz) is suitable because it can form a high-quality gate insulating layer 138 that is dense and has a high dielectric strength. This is because the high-purity oxide semiconductor layer and the high-quality gate insulating layer are in close contact with each other, so that the interface state can be reduced and the interface characteristics can be improved.

Of course, as long as a high-quality insulating layer can be formed as the gate insulating layer 138, other methods such as a sputtering method and a plasma CVD method should be applied even when a highly purified oxide semiconductor layer is used. Can be done. Further, an insulating layer whose interface characteristics with the film quality and the oxide semiconductor layer are modified by heat treatment after formation may be applied. In any case, the film quality of the gate insulating layer 138 may be good, the interface level density with the oxide semiconductor layer may be reduced, and a material capable of forming a good interface may be formed.

Next, an oxide semiconductor layer is formed on the gate insulating layer 138, and the oxide semiconductor layer is processed by a method such as etching using a mask to form an island-shaped oxide semiconductor layer 140 (FIG. 5). See (E)).

Examples of the oxide semiconductor layer include In-Sn-Ga-Zn-O series, which are quaternary metal oxides, In-Ga-Zn-O series, which are ternary metal oxides, and In-Sn-Zn. -O system, In-Al-Zn-O system, Sn-Ga-Zn-O system, Al-Ga-Zn-O system, Sn-Al-Zn-O system, and In, which is a binary metal oxide. -Zn-O series, Sn-Zn-O series, Al-Zn-O series, Zn-Mg-O series, Sn-Mg-O series, In-Mg-O series, and In, which is a unified metal oxide. It can be formed by using oxide semiconductors such as -O-based, Sn-O-based, and Zn-O-based. Further, the oxide semiconductor containing SiO2 may be used.

In addition, as an oxide semiconductor layer, InMO₃(ZnO)_mA thin film containing the material represented by (m&gt; 0) can be used. Here, M represents one or more metal elements selected from Ga, Al, Mn and Co. For example, as M, Ga, Ga and Al, Ga and Mn, Ga and Co and the like can be applied.

In the present embodiment, an amorphous oxide semiconductor layer is formed by a sputtering method using an In-Ga-Zn-O-based metal oxide target as the oxide semiconductor layer. By adding silicon to the amorphous oxide semiconductor layer, its crystallization can be suppressed. Therefore, for example, SiO₂The oxide semiconductor layer may be formed by using a target containing 2% by weight or more and 10% by weight or less.

As a metal oxide target for producing an oxide semiconductor layer by a sputtering method, for example, In₂O₃: Ga₂O₃A metal oxide target having a composition ratio such as: ZnO = 1: 1: 1 [mol ratio] can be used. Besides, In₂O₃: Ga₂O₃: ZnO = 1: 1: 2 [mol ratio], or In₂O₃: Ga₂O₃A metal oxide target having a composition ratio of: ZnO = 1: 1: 4 [mol ratio] may be used. The filling rate of the metal oxide target is 90% or more and 100% or less, preferably 95% or more (for example, 99.9%). By using a metal oxide target having a high filling rate, a dense oxide semiconductor layer is formed.

The atmosphere for forming the oxide semiconductor layer is preferably a rare gas (typically argon) atmosphere, an oxygen atmosphere, or a mixed atmosphere of a rare gas (typically argon) and oxygen. Specifically, for example, it is preferable to use a high-purity gas from which impurities such as hydrogen, water, hydroxyl groups, and hydrides have been removed to several ppm or less (preferably several ppb or less).

When forming the oxide semiconductor layer, the substrate is held in a processing chamber kept under reduced pressure, and the substrate temperature is set to 100 ° C or more and 600 ° C or less, preferably 200 ° C or more and 400 ° C or less. By forming the oxide semiconductor layer while heating the substrate, the concentration of impurities contained in the oxide semiconductor layer can be reduced. In addition, damage due to sputtering is reduced. Then, hydrogen and a sputter gas from which water has been removed are introduced while removing water in the treatment chamber, and an oxide semiconductor layer is formed by targeting the metal oxide.

In order to remove the water in the treatment chamber, it is preferable to use an adsorption type vacuum pump. For example, a cryopump, an ion pump, and a titanium sublimation pump can be used. Further, the exhaust means may be a turbo pump to which a cold trap is added. In the film formation chamber exhausted using a cryopump, for example, hydrogen atoms and water (H)₂Since a compound containing a hydrogen atom (more preferably a compound containing a carbon atom) such as O) is exhausted, the concentration of impurities contained in the oxide semiconductor layer formed in the film forming chamber can be reduced.

As the formation conditions, for example, the distance between the substrate and the target is 100 mm, the pressure is 0.6 Pa, the direct current (DC) power is 0.5 kW, and the atmosphere is an oxygen (oxygen flow rate ratio 100%) atmosphere. Can be done. It is preferable to use a pulsed direct current (DC) power supply because it can reduce dust and reduce the film thickness distribution. The thickness of the oxide semiconductor layer is 2 nm or more and 200 nm or less, preferably 5 nm or more and 30 nm or less. Since the appropriate thickness differs depending on the oxide semiconductor material to be applied, the thickness may be appropriately selected according to the material to be used.

Before forming the oxide semiconductor layer by the sputtering method, it is preferable to introduce argon gas and perform reverse sputtering to generate plasma to remove dust adhering to the surface of the gate insulating layer 138. is there. Here, the reverse sputtering refers to a method in which ions collide with a sputtering target in normal sputtering, and conversely, the surface is modified by colliding ions with the treated surface. As a method of colliding ions with the treated surface, there is a method of applying a high frequency voltage to the treated surface side in an argon atmosphere to generate plasma in the vicinity of the substrate. Nitrogen, helium, oxygen or the like may be used instead of the argon atmosphere.

Either dry etching or wet etching may be used for etching the oxide semiconductor layer. Of course, both can be used in combination. Etching conditions (etching gas, etching solution, etching time, temperature, etc.) are appropriately set according to the material so that etching can be performed in a desired shape.

Etching gas used for dry etching includes, for example, a gas containing chlorine (chlorine-based gas, for example, chlorine (Cl).₂), Boron trichloride (BCl)₃), Silicon tetrachloride (SiCl)₄), Carbon tetrachloride (CCl₄) Etc.) and so on. In addition, a gas containing fluorine (fluorine-based gas, for example, carbon tetrafluoride (CF)₄), Sulfur hexafluoride (SF₆), Nitrogen trifluoride (NF₃), Trifluoromethane (CHF)₃) Etc.), hydrogen bromide (HBr), oxygen (O₂), A gas obtained by adding a rare gas such as helium (He) or argon (Ar) to these gases may be used.

As the dry etching method, a parallel plate type RIE (Reactive Ion Etching) method or an ICP (Inductively Coupled Plasma) etching method can be used. Etching conditions (the amount of power applied to the coil-shaped electrode, the amount of power applied to the electrode on the substrate side, the electrode temperature on the substrate side, etc.) are appropriately set so that the etching can be performed in a desired shape.

As the etching solution used for wet etching, a solution obtained by mixing phosphoric acid, acetic acid and nitric acid, ammonia superwater (mixed solution of ammonia, water and hydrogen peroxide solution) and the like can be used. Further, an etching solution such as ITO07N (manufactured by Kanto Chemical Co., Inc.) may be used.

Next, it is desirable to perform the first heat treatment on the oxide semiconductor layer. The oxide semiconductor layer can be dehydrated or dehydrogenated by this first heat treatment. The temperature of the first heat treatment is 300 ° C or more and 800 ° C or less, preferably 400 ° C or more and 700 ° C or less, more preferably 450 ° C or more and 700 ° C or less, and more preferably 550 ° C or more and 700 ° C or less. It can be as follows.

By setting the temperature of the first heat treatment to 350 ° C. or higher, the oxide semiconductor layer can be dehydrated or dehydrogenated, and the hydrogen concentration in the oxide semiconductor layer can be reduced. Further, by setting the temperature of the first heat treatment to 450 ° C. or higher, the hydrogen concentration in the oxide semiconductor layer can be further reduced. Further, by setting the temperature of the first heat treatment to 550 ° C. or higher, the hydrogen concentration in the oxide semiconductor layer can be further reduced. For example, the substrate is introduced into an electric furnace using a resistance heating element or the like, and the oxide semiconductor layer 140 is heat-treated at 450 ° C. for 1 hour under a nitrogen atmosphere. During this period, the oxide semiconductor layer 140 does not come into contact with the atmosphere and prevents water and hydrogen from being remixed.

The heat treatment apparatus is not limited to the electric furnace, and may be an apparatus for heating the object to be processed by heat conduction from a medium such as heated gas or heat radiation. For example, an RTA (Rapid Thermal Anneal) device such as a GRTA (Gas Rapid Thermal Anneal) device or an LRTA (Lamp Rapid Thermal Anneal) device can be used.

The LRTA device is a device that heats an object to be processed by radiating light (electromagnetic waves) emitted from lamps such as halogen lamps, metal halide lamps, xenon arc lamps, carbon arc lamps, high-pressure sodium lamps, and high-pressure mercury lamps. The GRTA device is a device that performs heat treatment using a high-temperature gas. As the gas, a rare gas such as argon or an inert gas such as nitrogen that does not react with the object to be treated by heat treatment is used.

For example, as the first heat treatment, a GRTA treatment is performed in which the substrate is placed in an inert gas atmosphere heated to a high temperature of 650 ° C to 700 ° C, heated for several minutes, and then the substrate is taken out from the inert gas atmosphere. You may. The GRTA treatment enables high temperature heat treatment in a short time. Further, since the heat treatment is performed for a short time, it can be applied even under temperature conditions exceeding the strain point of the substrate. For example, when an SOI substrate containing a substrate having relatively low heat resistance such as a glass substrate is used, shrinkage of the substrate becomes a problem at a temperature exceeding the heat resistant temperature (distortion point), but in the case of short-time heat treatment, this is a problem. It doesn't matter.

As the inert gas atmosphere in which the first heat treatment is performed, an atmosphere containing nitrogen or a rare gas (helium, neon, argon, etc.) as a main component and not containing water, hydrogen, etc. is applied. Is desirable. For example, the purity of nitrogen or a rare gas such as helium, neon, or argon to be introduced into the heat treatment apparatus is 6N (99.9999%) or more, preferably 7N (99.99999%) or more (that is, the impurity concentration is 1ppm or less, preferably 0.1. ppm or less).

During the treatment, the atmosphere of the inert gas may be switched to an atmosphere containing oxygen. For example, when an electric furnace is used for the first heat treatment, the atmosphere can be switched when the temperature of the heat treatment is lowered. For example, the atmosphere during heat treatment (constant temperature) can be an inert gas atmosphere such as nitrogen or a rare gas (helium, neon, argon, etc.), and can be switched to an atmosphere containing oxygen when the temperature is lowered. As the atmosphere containing oxygen, oxygen gas or a gas obtained by mixing oxygen gas and nitrogen gas can be used. Even when this oxygen-containing atmosphere is used, it is preferable that the atmosphere does not contain water, hydrogen, or the like. Alternatively, the purity of the oxygen gas and nitrogen gas used is preferably 6N (99.9999%) or more, preferably 7N (99.99999%) or more (that is, the impurity concentration is 1ppm or less, preferably 0.1ppm or less). By performing the first heat treatment in an atmosphere containing oxygen, defects caused by oxygen deficiency can be reduced.

Depending on the conditions of the first heat treatment or the material of the oxide semiconductor layer, the oxide semiconductor layer may crystallize into microcrystals or polycrystals. For example, it may be a microcrystalline oxide semiconductor layer having a crystallization rate of 90% or more, or 80% or more. Further, depending on the conditions of the first heat treatment or the material of the oxide semiconductor layer, an amorphous oxide semiconductor layer containing no crystal component may be obtained.

Further, in the case of an oxide semiconductor layer in which fine crystals (particle size 1 nm or more and 20 nm or less (typically 2 nm or more and 4 nm or less)) are mixed in an amorphous oxide semiconductor (for example, the surface of the oxide semiconductor layer). There is also.

It is also possible to change the electrical characteristics of the oxide semiconductor layer by arranging microcrystals in amorphous. For example, when an oxide semiconductor layer is formed using an In-Ga-Zn-O-based metal oxide target, In has electrical anisotropy.₂Ga₂ZnO₇By forming a microcrystal region in which the crystal grains of the above are oriented, the electrical characteristics of the oxide semiconductor layer can be changed.

For example, In₂Ga₂ZnO₇By orienting the c-axis so as to take a direction perpendicular to the surface of the oxide semiconductor layer, the conductivity in the direction parallel to the surface of the oxide semiconductor layer is improved, and the direction perpendicular to the surface of the oxide semiconductor layer is improved. Insulation can be improved. Further, such a microcrystal region has a function of suppressing the invasion of impurities such as water and hydrogen into the oxide semiconductor layer.

The oxide semiconductor layer having the above-mentioned microcrystalline region can be formed by surface heating of the oxide semiconductor layer by GRTA treatment. Further, it can be more preferably formed by using a sputtering target having a Zn content smaller than that of In or Ga.

The first heat treatment on the oxide semiconductor layer 140 can also be performed on the oxide semiconductor layer before being processed into the island-shaped oxide semiconductor layer 140. In that case, after the first heat treatment, the substrate is taken out from the heating device and a photolithography step is performed.

Since the heat treatment has the effect of dehydrating and dehydrogenating the oxide semiconductor layer 140, it can also be called a dehydration treatment, a dehydrogenation treatment, or the like. In such dehydration treatment and dehydrogenation treatment, after the oxide semiconductor layer is formed, the source electrode or drain electrode is laminated on the oxide semiconductor layer 140, and then a protective insulating layer is provided on the source electrode or drain electrode. After forming, it can be performed at a timing such as. Further, such dehydration treatment and dehydrogenation treatment may be performed not only once but also a plurality of times.

Next, the source electrode or drain electrode 142a and the source electrode or drain electrode 142b are formed so as to be in contact with the oxide semiconductor layer 140 (see FIG. 5 (F)). The source electrode or drain electrode 142a and the source electrode or drain electrode 142b can be formed by forming a conductive layer so as to cover the oxide semiconductor layer 140 and then selectively etching the conductive layer.

The conductive layer can be formed by using a PVD (Physical Vapor Deposition) method such as a sputtering method or a CVD (Chemical Vapor Deposition) method such as a plasma CVD method. Further, as the material of the conductive layer, an element selected from aluminum, chromium, copper, tantalum, titanium, molybdenum, and tungsten, an alloy containing the above-mentioned element as a component, and the like can be used. A material selected from any one or more of manganese, magnesium, zirconium, beryllium and yttrium may be used. Further, a material may be used in which a single element or a combination of a plurality of elements selected from titanium, tantalum, tungsten, molybdenum, chromium, neodymium and scandium is used for aluminum.

Further, the conductive layer may be formed by using an oxide conductive film. As the oxide conductive film, indium oxide (In)₂O₃), Tin oxide (SnO)₂), Zinc oxide (ZnO), Indium tin oxide alloy (In₂O₃SnO₂, Sometimes abbreviated as ITO), Indium tin oxide alloy (In₂O₃-ZnO), or those in which silicon or silicon oxide is contained in these metal oxide materials can be used.

In this case, it is preferable to use a material having a high conductivity or a low resistivity as the oxide conductive film as compared with the material used for the oxide semiconductor layer 140. The conductivity of the oxide conductive film can be increased by increasing the carrier concentration. The carrier concentration of the oxide conductive film can be increased by increasing the hydrogen concentration. Further, the carrier concentration of the oxide conductive film can be increased by increasing the oxygen deficiency.

The conductive layer may have a single-layer structure or a laminated structure of two or more layers. Examples thereof include a single-layer structure of an aluminum film containing silicon, a two-layer structure in which a titanium film is laminated on an aluminum film, and a three-layer structure in which a titanium film, an aluminum film, and a titanium film are laminated. Here, a three-layer structure of a titanium film, an aluminum film, and a titanium film is applied.

An oxide conductor layer may be formed between the oxide semiconductor layer 140 and the conductive layer. The oxide conductor layer and the conductive layer can be continuously formed (continuous film formation). By providing such an oxide conductive layer, it is possible to reduce the resistance of the source region or the drain region, so that high-speed operation of the transistor is realized.

The conductive layer is then selectively etched to form the source or drain electrode 142a and the source or drain electrode 142b (see FIG. 5F). It is preferable to use ultraviolet rays, KrF laser light, or ArF laser light for exposure at the time of forming a mask used for etching.

The channel length (L) of the transistor is determined by the distance between the lower end of the source or drain electrode 142a and the lower end of the source or drain electrode 142b. When exposure is performed so that the channel length (L) is less than 25 nm, mask formation exposure is performed using Extreme Ultraviolet, which has an extremely short wavelength of several nm to several tens of nm. Exposure with ultra-ultraviolet rays has a high resolution and a large depth of focus. Therefore, it is possible to design the channel length (L) of the transistor to be formed later to be less than 25 nm, that is, the channel length (L) can be 10 nm or more and 1000 nm or less, and the circuit can be designed. The operating speed can be increased. Furthermore, since the off-current value is extremely small, the power consumption does not need to be large.

When etching the conductive layer, the respective materials and etching conditions are appropriately adjusted so that the oxide semiconductor layer 140 is not removed. Depending on the material and the etching conditions, a part of the oxide semiconductor layer 140 may be etched to form an oxide semiconductor layer having grooves (recesses) in the process.

Further, in order to reduce the number of times the mask is used and the number of steps, a resist mask may be formed by a multi-gradation mask which is an exposure mask in which transmitted light has a plurality of intensities, and an etching step may be performed using this. .. The resist mask formed by using the multi-gradation mask has a shape having a plurality of thicknesses (stepped shape) and can be further deformed by ashing, so that it can be used in a plurality of etching steps for processing different patterns. That is, one multi-tone mask can form a resist mask corresponding to at least two or more different patterns. Therefore, the number of exposure masks can be reduced, and the corresponding photolithography process can also be reduced, so that the process can be simplified.

After the above step, N₂O, N₂, Or plasma treatment using a gas such as Ar is preferable. By the plasma treatment, water and the like adhering to the surface of the exposed oxide semiconductor layer are removed. Alternatively, plasma treatment may be performed using a mixed gas of oxygen and argon.

Next, the protective insulating layer 144 is formed in contact with a part of the oxide semiconductor layer 140 without being exposed to the atmosphere (see FIG. 5 (G)).

The protective insulating layer 144 can be formed by appropriately using a method such as a sputtering method in which impurities such as water and hydrogen are not mixed into the protective insulating layer 144. The thickness shall be at least 1 nm or more. Examples of the material that can be used for the protective insulating layer 144 include silicon oxide, silicon nitride, silicon nitride nitride, and silicon nitride. Further, the structure may be a single-layer structure or a laminated structure. The substrate temperature at which the protective insulating layer 144 is formed is preferably room temperature or higher and 300 ° C. or lower, and the atmosphere is a noble gas (typically argon) atmosphere, an oxygen atmosphere, or a rare gas (typically). It is preferable to use a mixed atmosphere of argon) and oxygen.

When hydrogen is contained in the protective insulating layer 144, the hydrogen penetrates into the oxide semiconductor layer and oxygen is extracted from the oxide semiconductor layer by hydrogen, so that the back channel side of the oxide semiconductor layer has a low resistance. Therefore, a parasitic channel may be formed. Therefore, it is important not to use hydrogen in the forming method so that the protective insulating layer 144 does not contain hydrogen as much as possible.

Further, it is preferable to form the protective insulating layer 144 while removing the moisture in the treatment chamber. This is to prevent the oxide semiconductor layer 140 and the protective insulating layer 144 from containing hydrogen, a compound containing a hydroxyl group, or water.

In order to remove the water in the treatment chamber, it is preferable to use an adsorption type vacuum pump. For example, it is preferable to use a cryopump, an ion pump, or a titanium sublimation pump. Further, the exhaust means may be a turbo pump to which a cold trap is added. The film forming chamber exhausted by using the cryopump is, for example, hydrogen atoms or water (H).₂Since compounds containing hydrogen atoms such as O) are removed, the concentration of impurities contained in the protective insulating layer 144 formed in the film forming chamber can be reduced.

As the sputter gas used when forming the protective insulating layer 144, use a high-purity gas in which impurities such as hydrogen, water, a compound containing a hydroxyl group or a hydride are removed to 1 ppm or less (preferably 1 ppb or less). Is preferable.

Next, it is desirable to perform a second heat treatment (preferably 200 ° C or more and 400 ° C or less, for example, 250 ° C or more and 350 ° C or less) in an inert gas atmosphere or an oxygen gas atmosphere. For example, a second heat treatment is performed at 250 ° C. for 1 hour in a nitrogen atmosphere. When the second heat treatment is performed, the variation in the electrical characteristics of the transistor can be reduced.

Further, heat treatment may be performed in the atmosphere at 100 ° C. or higher and 200 ° C. or lower, for 1 hour or longer and 30 hours or shorter. This heat treatment may be performed while maintaining a constant heating temperature, or the temperature may be raised from room temperature to a heating temperature of 100 ° C or more and 200 ° C or less, and the temperature may be lowered from the heating temperature to room temperature multiple times. You may. Further, this heat treatment may be performed under reduced pressure before forming the protective insulating layer. When the heat treatment is performed under reduced pressure, the heating time can be shortened. The heat treatment may be performed in place of the second heat treatment, or may be performed before or after the second heat treatment.

Next, the interlayer insulating layer 146 is formed on the protective insulating layer 144 (see FIG. 6 (A)). The interlayer insulating layer 146 can be formed by using a PVD method, a CVD method, or the like. Further, it can be formed by using a material containing an inorganic insulating material such as silicon oxide, silicon nitride oxide, silicon nitride, hafnium oxide, aluminum oxide, and tantalum oxide. After the interlayer insulating layer 146 is formed, it is desirable to flatten the surface thereof by a method such as CMP or etching.

Next, openings are formed in the interlayer insulating layer 146, the protective insulating layer 144, and the gate insulating layer 138 to reach the electrode 136a, the electrode 136b, the electrode 136c, the source electrode or the drain electrode 142a, and the source electrode or the drain electrode 142b. , The conductive layer 148 is formed so as to be embedded in the opening (see FIG. 6 (B)). The opening can be formed by a method such as etching using a mask. The mask can be formed by a method such as exposure using a photomask.

Either wet etching or dry etching may be used as the etching, but from the viewpoint of microfabrication, it is preferable to use dry etching. The conductive layer 148 can be formed by using a film forming method such as a PVD method or a CVD method. Materials that can be used to form the conductive layer 148 include conductive materials such as molybdenum, titanium, chromium, tantalum, tungsten, aluminum, copper, neodymium, and scandium, and alloys and compounds (for example, nitrides) thereof. Can be mentioned.

Specifically, for example, a method of forming a thin titanium film by the PVD method in a region including an opening, forming a thin titanium nitride film by the CVD method, and then forming a tungsten film so as to be embedded in the opening can be applied. it can. Here, the titanium film formed by the PVD method reduces the oxide film at the interface with the interlayer insulating layer 146, and lower electrodes (here, electrodes 136a, 136b, electrodes 136c, source electrode or drain electrode 142a, source). It has a function of reducing contact resistance with the electrode or drain electrode 142b). Further, the titanium nitride film formed thereafter has a barrier function of suppressing the diffusion of the conductive material. Further, after forming a barrier film made of titanium, titanium nitride or the like, a copper film may be formed by a plating method.

After forming the conductive layer 148, a part of the conductive layer 148 is removed by a method such as etching or CMP to expose the interlayer insulating layer 146, so that the electrode 150a, the electrode 150b, the electrode 150c, the electrode 150d, and the electrode 150e are exposed. (See Fig. 6 (C)). When the electrode 150a, the electrode 150b, the electrode 150c, the electrode 150d, and the electrode 150e are formed by removing a part of the conductive layer 148, it is desirable to process the surface so that the surface becomes flat. By flattening the surfaces of the interlayer insulating layer 146, the electrode 150a, the electrode 150b, the electrode 150c, the electrode 150d, and the electrode 150e in this way, a good electrode, wiring, insulating layer, semiconductor layer, etc. can be obtained in a later process. It becomes possible to form.

Further, an insulating layer 152 is formed, an opening reaching the electrode 150a, an electrode 150b, an electrode 150c, an electrode 150d, and an electrode 150e is formed in the insulating layer 152, a conductive layer is formed so as to be embedded in the opening, and then etching is performed. A part of the conductive layer is removed by a method such as CMP or CMP to expose the insulating layer 152 to form electrodes 154a, 154b, electrodes 154c, and electrodes 154d (see FIG. 6 (D)). Since the step is the same as the case of forming the electrode 150a or the like, the details will be omitted.

When the transistor 402 is manufactured by the above method, the hydrogen concentration of the oxide semiconductor layer 140 is 5 × 10.¹⁹/cm³The off-current of the transistor 402 at room temperature is 1 × 10.^-13It becomes A or less. The carrier concentration of the oxide semiconductor layer is 1 × 10.¹⁴/cm³Will be less than. By applying the oxide semiconductor layer 140 in which the hydrogen concentration is sufficiently reduced, oxygen is supplied, and the purity is high, the transistor 402 having excellent characteristics can be obtained. Further, since the lower part has a transistor 160 using a material other than an oxide semiconductor and the upper part has a transistor 402 using an oxide semiconductor, a non-volatile latch circuit having excellent characteristics having both characteristics and a non-volatile latch circuit thereof are provided. The semiconductor device used can be manufactured.

If oxygen is supplied to the oxide semiconductor layer 140 immediately after the hydrogen concentration is reduced, there is no risk of hydrogen or water being mixed into the oxide semiconductor layer, so that the oxide semiconductor has extremely good characteristics. It is preferable in that a layer can be realized. Of course, if the oxide semiconductor layer having good characteristics can be realized, the hydrogen concentration reduction treatment and the oxygen supply treatment do not need to be continuously performed. For example, another process may be included between these processes. Further, these processes may be performed at the same time.

As a semiconductor material that can be compared with an oxide semiconductor, there is silicon carbide (for example, 4H-SiC). Oxide semiconductors and 4H-SiC have some things in common. Carrier density is one example. According to the Fermi-Dirac distribution, the minority carriers of oxide semiconductors are 1 × 10.^-7/cm³It is estimated to be about 6.7 × 10 in 4H-SiC.^-11/cm³Similar to, it is an extremely low value. Intrinsic carrier density of silicon (1.4 x 10)¹⁰/cm³It is easy to understand that the degree is extraordinary when compared with the degree).

In addition, the energy bandgap of oxide semiconductors is 3.0 to 3.5eV, and the energy bandgap of 4H-SiC is 3.26eV. Therefore, oxide semiconductors and silicon carbide are common in terms of wide-gap semiconductors. There is.

On the other hand, there are extremely large differences between oxide semiconductors and silicon carbide. It is the process temperature. Since a semiconductor process using silicon carbide generally requires a heat treatment of 1500 ° C to 2000 ° C, it is difficult to form a laminated structure with a semiconductor element using another semiconductor material. This is because the semiconductor substrate, the semiconductor element, and the like are destroyed at such a high temperature. On the other hand, oxide semiconductors can be manufactured by heat treatment at 300 to 500 ° C (below the glass dislocation temperature, at most 700 ° C), and after forming an integrated circuit using other semiconductor materials. , It becomes possible to form a semiconductor element made of an oxide semiconductor.

Further, unlike the case of silicon carbide, there is an advantage that a substrate having low heat resistance such as a glass substrate can be used. Further, it has an advantage that the energy cost can be sufficiently lowered as compared with silicon carbide in that heat treatment at a high temperature is not required.

In oxide semiconductors, many studies on physical properties such as DOS (density of state) have been carried out, but these studies do not include the idea of sufficiently reducing the localized level itself. In one aspect of the disclosed invention, a highly purified oxide semiconductor is produced by removing water and hydrogen, which may cause a localized level, from the oxide semiconductor. This is based on the idea of sufficiently reducing the localized level itself. And this makes it possible to manufacture extremely excellent industrial products.

Furthermore, by supplying oxygen to the unpaired bond of the metal generated by oxygen deficiency and reducing the localization level due to oxygen defects, a more purified (i-type) oxide semiconductor is obtained. It is possible. For example, it is possible to form an oxygen-rich oxide film in close contact with the channel formation region and supply oxygen from the oxide film to reduce the localization level due to oxygen defects.

Defects in oxide semiconductors are attributed to shallow levels of 0.1 to 0.2 eV below the conduction band due to excess hydrogen and deep levels due to lack of oxygen. In order to eliminate these defects, the technical idea of thoroughly removing hydrogen and supplying sufficient oxygen is considered to be correct.

Further, although the oxide semiconductor is generally n-type, in one aspect of the disclosed invention, i-type is realized by removing impurities, particularly water and hydrogen. In this respect, it can be said that it includes an unprecedented technical idea rather than the i-type by adding impurities like silicon.

Further, in the above, among the elements included in the non-volatile latch circuit 400, the elements other than the transistor 402 using the oxide semiconductor have shown an example in which a material other than the oxide semiconductor is used as the semiconductor material. It is not limited to this. Among the elements included in the non-volatile latch circuit 400, it is also possible to use an oxide semiconductor as the semiconductor material in the elements other than the transistor 402.

&lt;Conduction Mechanism of Transistor Using Oxide Semiconductor&gt; Here, the conduction mechanism of the transistor using the oxide semiconductor will be described with reference to FIGS. 7 to 10. In the following explanation, an ideal situation is assumed for easy understanding, and not all of them reflect the actual situation. It should be added that the following explanation is merely a consideration and does not affect the effectiveness of the invention.

FIG. 7 is a cross-sectional view of a transistor (thin film transistor) using an oxide semiconductor. An oxide semiconductor layer (OS) is provided on the gate electrode (GE1) via a gate insulating layer (GI), and a source electrode (S) and a drain electrode (D) are provided on the oxide semiconductor layer (OS). An insulating layer is provided so as to cover the drain electrode (D).

FIG. 8 shows an energy band diagram (schematic diagram) in the AA'cross section of FIG. In addition, black circles () in FIG. 8 indicate electrons, white circles () indicate holes, and each has an electric charge (-q, + q). Positive voltage on the drain electrode (V)_DWhen&gt; 0) is applied and no voltage is applied to the gate electrode (V)_G= 0), the solid line is the positive voltage (V) on the gate electrode_GThe case where&gt; 0) is applied is shown. When no voltage is applied to the gate electrode, carriers (electrons) are not injected from the electrode to the oxide semiconductor side due to a high potential barrier, indicating an off state in which no current flows. On the other hand, when a positive voltage is applied to the gate, the potential barrier is lowered, indicating an on state in which a current flows.

FIG. 9 shows an energy band diagram (schematic diagram) in the cross section of B-B'in FIG. 7. Figure 9 (A) shows the positive voltage (V) at the gate electrode (GE1)._G&gt; 0) is given, indicating an on state in which carriers (electrons) flow between the source electrode and the drain electrode. In addition, Fig. 9 (B) shows the negative voltage (V) at the gate electrode (GE1)._GThe case where &lt;0) is applied and the off state (a state in which a small number of carriers do not flow) is shown.

Figure 10 shows the vacuum level and the work function of the metal (φ)._M), The relationship between the electron affinity (χ) of the oxide semiconductor is shown. At room temperature, the electrons in the metal are degenerate, and the Fermi level is located in the conduction band. On the other hand, conventional oxide semiconductors are n-type, and their Fermi level (E)._F) Is the true Fermi level (E) located in the center of the bandgap._i), And is located closer to the conduction band. It is known that a part of hydrogen in an oxide semiconductor becomes a donor and is one of the factors for n-type formation.

On the other hand, the oxide semiconductor according to one aspect of the disclosed invention removes hydrogen, which is a factor of n-type formation, from the oxide semiconductor, and contains elements (impurity elements) other than the main component of the oxide semiconductor as much as possible. It is made genuine (type i) or substantially genuine by purifying it so that it does not exist. That is, it is characterized in that it does not add an impurity element to form an i-type, but removes impurities such as hydrogen and water as much as possible to bring it closer to a highly purified i-type semiconductor (intrinsic semiconductor). This results in the Fermi level (E)_F) Is the true Fermi level (E)_i) Can be the same.

Oxide semiconductor bandgap (E_g) Is 3.15 eV, and the electron affinity (χ) is said to be 4.3 eV. The work function of titanium (Ti) that constitutes the source electrode and drain electrode is approximately equal to the electron affinity (χ) of the oxide semiconductor. In this case, a Schottky type barrier is not formed for electrons at the metal-oxide semiconductor interface.

At this time, as shown in FIG. 9A, the electrons move near the interface between the gate insulating layer and the highly purified oxide semiconductor (the lowest energy-stable portion of the oxide semiconductor).

Further, as shown in FIG. 9B, when a negative potential is applied to the gate electrode (GE1), the number of holes, which are minority carriers, is substantially zero, so that the current is as close to zero as possible. It becomes.

By purifying the element (impurity element) other than the main component of the oxide semiconductor as much as possible in this way, it becomes intrinsic (i type) or substantially intrinsic, and therefore the interface with the gate insulating layer. Characteristics are important. Therefore, the gate insulating layer is required to have a good interface with the oxide semiconductor. Specifically, for example, it is preferable to use an insulating layer produced by a CVD method using a high-density plasma generated in a power frequency of the VHF band to a microwave band, an insulating layer produced by a sputtering method, or the like. ..

By improving the interface between the oxide semiconductor and the gate insulating layer while purifying the oxide semiconductor, for example, the channel width (W) of the transistor is 1 × 10.⁴1 × 10 when μm and channel length (L) are 3 μm^-13A subthreshold swing value (S value) (gate insulating layer thickness: 100 nm) with an off current of A or less and 0.1 V / dec. Can be realized.

In this way, by purifying the transistor so that elements other than the main component (impurity element) of the oxide semiconductor are not contained as much as possible, the operation of the transistor can be improved.

&lt;Hot carrier deterioration resistance of transistors using oxide semiconductors&gt; Next, hot carrier deterioration resistance of transistors using oxide semiconductors will be described with reference to FIGS. 11 to 13. In the following explanation, an ideal situation is assumed for easy understanding, and not all of them reflect the actual situation. It should be added that the following explanation is just one consideration.

Channel hot electron injection (CHE injection) and drain avalanche hot carrier injection (DAHC injection) are the main causes of hot carrier deterioration. In the following, for the sake of simplicity, only electrons will be considered.

CHE injection refers to a phenomenon in which electrons having energy equal to or higher than the barrier of the gate insulating layer in the semiconductor layer are injected into the gate insulating layer or the like. The donation of energy to an electron is performed by accelerating the electron in a low electric field.

DAHC injection refers to a phenomenon in which new electrons generated by collision of electrons accelerated by a high electric field are injected into a gate insulating layer or the like. The difference between DAHC injection and CHE injection is whether or not it involves avalanche breakdown due to collision ionization. Note that DAHC injection requires electrons with kinetic energy equal to or greater than the band gap of the semiconductor.

Figures 11 and 12 show the energy required for various hot carrier injections estimated from the band structure of silicon (Si) and In-Ga-Zn-O-based oxide semiconductor (IGZO). In FIGS. 11 and 12, the left represents CHE injection and the right represents DAHC injection.

In silicon, the deterioration due to DAHC injection is more serious than that due to CHE injection. This is due to the fact that silicon has a small bandgap and is prone to avalanche breakdown, whereas very few carriers (eg, electrons) are accelerated without collision in silicon. Due to the avalanche breakdown, the number of electrons that can cross the barrier of the gate insulating layer (that is, the electrons injected into the gate insulating layer) increases rapidly, which causes deterioration.

In In-Ga-Zn-O-based oxide semiconductors, the energy required for CHE injection is not significantly different from that in silicon, and the probability is still low. On the other hand, the energy required for DAHC injection increases by that amount because the bandgap is wider than that of silicon, and the avalanche breakdown itself is unlikely to occur. In other words, the probabilities of both CHE injection and DAHC injection are low, and hot carrier deterioration is less likely to occur compared to silicon.

By the way, the bandgap of the In-Ga-Zn-O-based oxide semiconductor is about the same as that of silicon carbide (SiC), which is attracting attention as a high pressure resistant material. Figure 13 shows the energy required for various hot carrier injections for 4H-SiC. Regarding CHE injection, In-Ga-Zn-O-based oxide semiconductors have a slightly higher threshold and can be said to be advantageous.

From the above, it can be seen that In-Ga-Zn-O-based oxide semiconductors are much more resistant to hot carrier deterioration and source-drain fracture than silicon. In addition, it can be said that a pressure resistance comparable to that of silicon carbide can be obtained.

&lt;Short-channel effect in a transistor using an oxide semiconductor&gt; Next, the short-channel effect in a transistor using an oxide semiconductor will be described with reference to FIGS. 14 and 15. In the following explanation, an ideal situation is assumed for easy understanding, and not all of them reflect the actual situation. It should be added that the following explanation is just one consideration.

The short-channel effect refers to the deterioration of electrical characteristics that becomes apparent as the transistor becomes finer (reduction of channel length (L)). The short-channel effect is due to the effect of the drain extending to the source. Specific examples of the short-channel effect include a decrease in the threshold voltage, an increase in the S value, and an increase in the leakage current.

Here, device simulation was used to verify the structure that can suppress the short-channel effect. Specifically, four types of models with different carrier concentrations and oxide semiconductor layer thickness were prepared, and the relationship between the channel length (L) and the threshold voltage (Vth) was confirmed. As a model, a bottom gate structure transistor is used, and the carrier concentration of the oxide semiconductor is 1.7 x 10.^-8/cm³, Or 1.0 × 10¹⁵/cm³The thickness of the oxide semiconductor layer was either 1 μm or 30 nm. An In-Ga-Zn-O-based oxide semiconductor was used as the oxide semiconductor, and a silicon oxide film having a thickness of 100 nm was used as the gate insulating layer. Band gap of oxide semiconductor is 3.15 eV, electron affinity is 4.3 eV, relative permittivity is 15, electron mobility is 10 cm.²Assumed / Vs. The relative permittivity of the silicon oxide nitride film was assumed to be 4.0. Silvaco's device simulation software "Atlas" was used for the calculation.

There is no big difference in the calculation results between the top gate structure and the bottom gate structure. The calculation results are shown in FIGS. 14 and 15. Figure 14 shows the carrier concentration of 1.7 × 10.^-8/cm³In the case of, in Fig. 15, the carrier concentration is 1.0 × 10.¹⁵/cm³This is the case. In FIGS. 14 and 15, the amount of change (ΔVth) in the threshold voltage (Vth) when the channel length (L) is changed from 10 μm to 1 μm is shown with reference to a transistor having a channel length (L) of 10 μm. Shown. As shown in Fig. 14, the carrier concentration of the oxide semiconductor is 1.7 × 10.^-8/cm³When the thickness of the oxide semiconductor layer was 1 μm, the amount of change in the threshold voltage (ΔVth) was -3.6 V. Moreover, as shown in FIG. 14, the carrier concentration of the oxide semiconductor is 1.7 × 10.^-8/cm³When the thickness of the oxide semiconductor layer was 30 nm, the amount of change in the threshold voltage (ΔVth) was -0.2 V. Further, as shown in FIG. 15, the carrier concentration of the oxide semiconductor is 1.0 × 10.¹⁵/cm³When the thickness of the oxide semiconductor layer was 1 μm, the amount of change in the threshold voltage (ΔVth) was -3.6 V. Further, as shown in FIG. 15, the carrier concentration of the oxide semiconductor is 1.0 × 10.¹⁵/cm³When the thickness of the oxide semiconductor layer was 30 nm, the amount of change in the threshold voltage (ΔVth) was -0.2 V. It can be said that the result shows that the short channel effect can be suppressed by reducing the thickness of the oxide semiconductor layer in the transistor using the oxide semiconductor. For example, when the channel length (L) is about 1 μm, even if the oxide semiconductor layer has a sufficiently high carrier concentration, the short channel effect can be sufficiently suppressed if the thickness is about 30 nm. Understood.

By using a transistor using the oxide semiconductor according to the present embodiment as a semiconductor material constituting the channel formation region in a non-volatile latch circuit as a switching element of the data holding unit, the temperature operating range is wide and stable even at high temperatures. It is possible to realize a non-volatile latch circuit that operates and the stored logical state does not disappear even when the power is turned off, or a latch circuit that incorporates a data holding unit having a sufficiently long refresh period.

Since data is written by switching transistors, there is virtually no limit to the number of rewrites. Further, the write voltage is about the threshold voltage of the transistor, and it is possible to operate at a low voltage. Further, since the potential of the data holding unit is directly applied, the variation in the amount of charge held as data can be suppressed to be small, and the data can be easily read out.

By using the non-volatile latch circuit, various logic circuits can be realized. For example, power consumption can be reduced by turning off the power of unused blocks. In addition, since the logical state is memorized even when the power is turned off, it is possible to start the system when the power is turned on and shut down the system when the power is turned off at high speed and with low power consumption. Is.

As described above, the configurations and methods shown in the present embodiment can be appropriately combined with the configurations and methods shown in other embodiments.

(Embodiment 2) In the present embodiment, the configuration, manufacturing method, and the like of the element included in the non-volatile latch circuit, which is one aspect of the disclosed invention, will be described with reference to FIGS. 16, 17, and 18. .. In the present embodiment, the configuration of the non-volatile latch circuit is the same as that in FIG.

FIG. 16 is a cross-sectional view showing an example of the configuration of the element included in the non-volatile latch circuit. FIG. 16 shows an example in which the configuration of the transistor 402 using the oxide semiconductor in the upper part is different from that in FIG. 3 among the elements included in the non-volatile latch circuit. That is, FIG. 16 shows an example in which the configuration of the transistor 402 using the upper oxide semiconductor is a top gate type transistor. Other configurations (such as the configuration of the lower transistor) are the same as in FIG.

&lt;Structure of Element of Non-Volatile Latch Circuit&gt; FIG. 16 has a transistor 160 using a material other than an oxide semiconductor at the lower part and a transistor 402 using an oxide semiconductor at the upper part. The transistor 160 using a material other than the oxide semiconductor can be used as a transistor constituting the first element (D1) 412 and the second element (D2) 413 included in the latch portion. High-speed operation is possible by using a material other than an oxide semiconductor. Other elements of the non-volatile latch circuit may have the same or similar configuration as the transistor 160.

Further, an element having a capacity of 404 or the like included in the non-volatile latch circuit can be formed by using a conductive film, a semiconductor film, an insulating film or the like constituting the transistor 402 or the transistor 160. Although the transistor 160 and the transistor 402 are both described as n-type transistors, a p-type transistor may be adopted. The transistor 160 can be easily made into a p-type.

The transistor 160 includes a channel forming region 116 provided on a substrate 100 containing a semiconductor material, an impurity region 114 provided so as to sandwich the channel forming region 116, and a high-concentration impurity region 120 (these are also simply referred to as an impurity region). ), The gate insulating layer 108a provided on the channel forming region 116, the gate electrode 110a provided on the gate insulating layer 108a, the source electrode or drain electrode 130a electrically connected to the impurity region 114, and It has a source electrode or a drain electrode 130b.

Here, a sidewall insulating layer 118 is provided on the side surface of the gate electrode 110a. Further, the region of the substrate 100 that does not overlap with the sidewall insulating layer 118 when viewed in a plane has a high-concentration impurity region 120 and a metal compound region 124 in contact with the high-concentration impurity region 120. Further, an element separation insulating layer 106 is provided on the substrate 100 so as to surround the transistor 160, and an interlayer insulating layer 126 and an interlayer insulating layer 128 are provided so as to cover the transistor 160.

The source electrode or drain electrode 130a and the source electrode or drain electrode 130b are electrically connected to the metal compound region 124 through openings formed in the interlayer insulating layer 126 and the interlayer insulating layer 128. That is, the source electrode or drain electrode 130a and the source electrode or drain electrode 130b are electrically connected to the high-concentration impurity region 120 and the impurity region 114 via the metal compound region 124.

The transistor 402 includes an oxide semiconductor layer 140 provided on the insulating layer 168, a source electrode or a drain electrode 142a provided on the oxide semiconductor layer 140 and electrically connected to the oxide semiconductor layer 140, and a source. An oxide semiconductor on the electrode or drain electrode 142b, the oxide semiconductor layer 140, the source electrode or drain electrode 142a, the gate insulating layer 166 provided so as to cover the source electrode or drain electrode 142b, and the gate insulating layer 166. It has a gate electrode 178 provided in a region that overlaps with layer 140 (see FIG. 16).

Here, it is desirable that the oxide semiconductor layer 140 is one in which impurities such as hydrogen are sufficiently removed, oxygen is supplied, and the purity is high. Specifically, the hydrogen concentration of the oxide semiconductor layer 140 measured by secondary ion mass spectrometry (SIMS) is 5 × 10.¹⁹/cm³Below, preferably 5x10¹⁸/cm³Below, more preferably 5x10¹⁷/cm³Below, more preferably 1x10¹⁶/cm³Try to be less than.

The oxide semiconductor layer 140 in which the hydrogen concentration is sufficiently reduced, oxygen is supplied, and the purity is high is found in a general silicon wafer (a silicon wafer to which a small amount of impurity elements such as phosphorus and boron are added). Carrier concentration (1 x 10)¹⁴/cm³A sufficiently small carrier concentration value (eg, 1x10) compared to the degree)¹²/cm³Less than, preferably 1x10¹¹/cm³Less than).

As described above, by using an i-shaped or substantially i-shaped oxide semiconductor, a transistor 402 having extremely excellent off-current characteristics can be obtained. For example, drain voltage V_DIs + 1V or + 10V and the gate voltage V_GIn the range of -5V to -20V, the off-current at room temperature is 1x10.^-13A or less. Further, the above-mentioned transistor has a normally-off transistor characteristic. Therefore, the off-current, that is, the leakage current when the voltage between the gate and the source electrode is almost 0 is significantly smaller than that of the transistor using silicon. For example, the unit channel width leakage current at room temperature is 10 aA / μm or less.

Further, in terms of temperature characteristics, it is possible to obtain a product in which the off-current is sufficiently low and the on-current is sufficiently high even at a high temperature. For example, V of transistor 402_G-I_DData have been obtained that the characteristics have little temperature dependence of on-current, mobility, and S value in the range of -25 ° C to 150 ° C. In addition, the off current is 1 × 10 in the above temperature range.^-13Very small data of A or less is obtained. One reason for this is that the oxide semiconductor used is one in which the hydrogen concentration is sufficiently reduced to be highly purified, the carrier concentration is sufficiently low, and the i-type or substantially i-type is used. it is conceivable that.

As described above, by applying the oxide semiconductor layer 140 whose hydrogen concentration is sufficiently reduced and purified, and reducing the off-current of the transistor 402, a semiconductor device having a new configuration can be realized.

Further, an interlayer insulating layer 170 and an interlayer insulating layer 172 are provided on the transistor 402. Here, the gate insulating layer 166, the interlayer insulating layer 170, and the interlayer insulating layer 172 are provided with openings reaching the source electrode or drain electrode 142a and the source electrode or drain electrode 142b, and the electrode 154d is provided through the openings. , Electrode 154e is formed in contact with the source electrode or drain electrode 142a and the source electrode or drain electrode 142b, respectively. Further, similarly to the electrode 154d and the electrode 154e, the electrode 136a, the electrode 136b, the electrode 154a in contact with the electrode 136c, the electrode 154b, and the electrode through the openings provided in the gate insulating layer 166, the interlayer insulating layer 170, and the interlayer insulating layer 172. 154c is formed.

Further, an insulating layer 156 is provided on the interlayer insulating layer 172, and electrodes 158a, 158b, electrodes 158c, and electrodes 158d are provided so as to be embedded in the insulating layer 156. Here, the electrode 158a is in contact with the electrode 154a, the electrode 158b is in contact with the electrode 154b, the electrode 158c is in contact with the electrode 154c and the electrode 154d, and the electrode 158d is in contact with the electrode 154e.

That is, the source electrode or drain electrode 142a of the transistor 402 is electrically connected to other elements (such as a transistor using a material other than an oxide semiconductor) via the electrode 130c, the electrode 136c, the electrode 154c, the electrode 158c, and the electrode 154d. It is connected to (see Figure 16). Further, the source electrode or drain electrode 142b of the transistor 402 is electrically connected to other elements via the electrodes 154e and 158d. The configuration of the electrodes (electrode 130c, electrode 136c, electrode 154c, electrode 158c, electrode 154d, etc.) related to the connection is not limited to the above, and can be added or omitted as appropriate.

&lt;Method of manufacturing the element of the non-volatile latch circuit&gt; Next, an example of the method of manufacturing the element of the non-volatile latch circuit will be described. The element included in the non-volatile latch circuit can be manufactured by the manufacturing method shown below. Since the method for manufacturing the transistor 160 is the same as that in FIG. 4, the description thereof will be omitted. A method for manufacturing the transistor 402 will be described with reference to FIG. 17 or FIG.

&lt;Method of Fabricating Upper Transistor&gt; Next, a step of manufacturing the transistor 402 on the interlayer insulating layer 128 will be described with reference to FIG. 17 or FIG. Since FIG. 17 or FIG. 18 shows various electrodes on the interlayer insulating layer 128 and the manufacturing process of the transistor 402 and the like, the transistor 160 and the like existing in the lower part of the transistor 402 are omitted.

First, the insulating layer 132 is formed on the interlayer insulating layer 128, the source electrode or drain electrode 130a, the source electrode or drain electrode 130b, and the electrode 130c. Then, an opening is formed in the insulating layer 132 to reach the source electrode or drain electrode 130a, the source electrode or drain electrode 130b, and the electrode 130c. Then, a conductive layer is formed so as to be embedded in the opening. Then, a part of the conductive layer is removed by a method such as etching treatment or CMP to expose the insulating layer 132 to form the electrode 136a, the electrode 136b, and the electrode 136c (see FIG. 17 (A)).

The insulating layer 132 can be formed by using a PVD method, a CVD method, or the like. Further, it can be formed by using a material containing an inorganic insulating material such as silicon oxide, silicon nitride oxide, silicon nitride, hafnium oxide, aluminum oxide, and tantalum oxide.

The opening of the insulating layer 132 can be formed by a method such as etching using a mask. The mask can be formed by a method such as exposure using a photomask. Either wet etching or dry etching may be used as the etching, but from the viewpoint of microfabrication, it is preferable to use dry etching.

The conductive layer can be formed by using a film forming method such as a PVD method or a CVD method. Examples of the material that can be used for forming the conductive layer include conductive materials such as molybdenum, titanium, chromium, tantalum, tungsten, aluminum, copper, neodymium, and scandium, and alloys and compounds (for example, nitrides) thereof. Be done.

More specifically, for example, a method of forming a thin titanium film by the PVD method in a region including an opening, forming a thin titanium nitride film by the CVD method, and then forming a tungsten film so as to be embedded in the opening is applied. Can be done. Here, the titanium film formed by the PVD method reduces the oxide film that can be formed on the surface of the lower electrode (here, source electrode or drain electrode 130a, source electrode or drain electrode 130b, electrode 130c, etc.) and lower electrode. It has a function of reducing contact resistance with.

Further, the titanium nitride film formed thereafter has a barrier function of suppressing the diffusion of the conductive material. Further, after forming a barrier film made of titanium, titanium nitride or the like, a copper film may be formed by a plating method. Not limited to the so-called single damascene method, a dual damascene method or the like may be applied.

When forming the electrodes 136a, 136b, and 136c, it is desirable to use CMP or the like to process the electrodes so that the surfaces are flat. By flattening the surfaces of the insulating layer 132, the electrode 136a, the electrode 136b, and the electrode 136c in this way, it is possible to form a good electrode, wiring, insulating layer, semiconductor layer, etc. in a later process. ..

Next, the insulating layer 168 is formed so as to cover the insulating layer 132, the electrode 136a, the electrode 136b, and the electrode 136c. Then, an oxide semiconductor layer is formed on the insulating layer 168, and the oxide semiconductor layer is processed by a method such as etching using a mask to form an island-shaped oxide semiconductor layer 140 (FIG. 17 (B). )reference).

The insulating layer 168 functions as a base and can be formed by using a CVD method, a sputtering method, or the like. Further, the insulating layer 168 is preferably formed so as to contain silicon oxide, silicon nitride, silicon oxide nitride, silicon nitride oxide, aluminum oxide, hafnium oxide, tantalum oxide and the like. The insulating layer 168 may have a single-layer structure or a laminated structure. The thickness of the insulating layer 168 is not particularly limited, but may be, for example, 10 nm or more and 500 nm or less. Here, since the insulating layer 168 is not an indispensable component, it is possible to configure the structure without the insulating layer 168.

If the insulating layer 168 contains hydrogen, water, or the like, hydrogen may invade the oxide semiconductor layer or oxygen may be extracted from the oxide semiconductor layer by hydrogen, which may deteriorate the characteristics of the transistor. .. Therefore, it is desirable that the insulating layer 168 is formed so as not to contain hydrogen or water as much as possible.

For example, when a sputtering method or the like is used, it is desirable to form the insulating layer 168 in a state where the moisture in the treatment chamber is removed. Further, in order to remove water in the treatment chamber, it is desirable to use an adsorption type vacuum pump such as a cryopump, an ion pump, or a titanium sublimation pump. A turbo pump with a cold trap added may be used. Since hydrogen, water, and the like are sufficiently removed from the treatment chamber exhausted by using a cryopump or the like, the concentration of impurities contained in the insulating layer 168 can be reduced.

Further, when forming the insulating layer 168, it is desirable to use a high-purity gas in which impurities such as hydrogen and water are reduced to several ppm or less (preferably 10 ppb or less).

Examples of the oxide semiconductor layer include In-Sn-Ga-Zn-O series, which are quaternary metal oxides, In-Ga-Zn-O series, which are ternary metal oxides, and In-Sn-Zn. -O system, In-Al-Zn-O system, Sn-Ga-Zn-O system, Al-Ga-Zn-O system, Sn-Al-Zn-O system, and In, which is a binary metal oxide. -Zn-O series, Sn-Zn-O series, Al-Zn-O series, Zn-Mg-O series, Sn-Mg-O series, In-Mg-O series, and In, which is a unified metal oxide. It can be formed by using oxide semiconductors such as -O-based, Sn-O-based, and Zn-O-based. Further, the oxide semiconductor containing SiO2 may be used.

In addition, as an oxide semiconductor layer, InMO₃(ZnO)_mA thin film containing the material represented by (m&gt; 0) can be used. Here, M represents one or more metal elements selected from Ga, Al, Mn and Co. For example, as M, Ga, Ga and Al, Ga and Mn, Ga and Co and the like can be applied.

In the present embodiment, an amorphous oxide semiconductor layer is formed by a sputtering method using an In-Ga-Zn-O-based metal oxide target as the oxide semiconductor layer. By adding silicon to the amorphous oxide semiconductor layer, its crystallization can be suppressed. Therefore, for example, SiO₂The oxide semiconductor layer may be formed by using a target containing 2% by weight or more and 10% by weight or less.

In₂O₃: Ga₂O₃A metal oxide target having a composition ratio such as: ZnO = 1: 1: 1 [mol ratio] can be used. In addition, In₂O₃: Ga₂O₃: ZnO = 1: 1: 2 [mol ratio], or In₂O₃: Ga₂O₃A metal oxide target having a composition ratio of: ZnO = 1: 1: 4 [mol ratio] may be used. The filling rate of the metal oxide target is 90% or more and 100% or less, preferably 95% or more (for example, 99.9%). By using a metal oxide target having a high filling rate, a dense oxide semiconductor layer is formed.

The atmosphere for forming the oxide semiconductor layer is preferably a rare gas (typically argon) atmosphere, an oxygen atmosphere, or a mixed atmosphere of a rare gas (typically argon) and oxygen. Specifically, for example, it is preferable to use a high-purity gas atmosphere in which impurities such as hydrogen, water, hydroxyl groups, and hydrides are removed to 1 ppm or less (preferably 1 ppb or less).

When forming the oxide semiconductor layer, the substrate is held in a processing chamber kept under reduced pressure, and the substrate temperature is heated to 100 ° C. or higher and 600 ° C. or lower, preferably 200 ° C. or higher and 400 ° C. or lower. Then, hydrogen and a sputter gas from which water has been removed are introduced while removing water in the treatment chamber, and an oxide semiconductor layer is formed by targeting the metal oxide. By forming the oxide semiconductor layer while heating the substrate, the concentration of impurities contained in the oxide semiconductor layer can be reduced. In addition, damage to the oxide semiconductor layer due to sputtering is reduced.

In order to remove the water in the treatment chamber, it is preferable to use an adsorption type vacuum pump. For example, a cryopump, an ion pump, a titanium sublimation pump, or the like can be used. Further, a turbo pump to which a cold trap is added may be used. In the treatment chamber exhausted by using the cryopump, hydrogen, water and the like are removed, and the concentration of impurities in the oxide semiconductor layer can be reduced.

The conditions for forming the oxide semiconductor layer are, for example, the distance between the substrate and the target is 100 mm, the pressure is 0.6 Pa, the direct current (DC) power is 0.5 kW, and the atmosphere is an oxygen (oxygen flow rate ratio 100%) atmosphere. Conditions can be applied. It is preferable to use a pulsed direct current (DC) power supply because it can reduce dust and reduce the film thickness distribution. The thickness of the oxide semiconductor layer is 2 nm or more and 200 nm or less, preferably 5 nm or more and 30 nm or less. However, since the appropriate thickness differs depending on the oxide semiconductor material to be applied, the application of the semiconductor device, etc., the thickness may be selected according to the material to be used, the application, and the like.

Before forming the oxide semiconductor layer by the sputtering method, it is preferable to introduce argon gas and perform reverse sputtering to generate plasma to remove deposits on the surface of the insulating layer 168. Here, the reverse sputtering refers to a method in which ions collide with a sputtering target in normal sputtering, and conversely, the surface is modified by colliding ions with the treated surface. As a method of colliding ions with the treated surface, there is a method of applying a high frequency voltage to the treated surface side in an argon atmosphere to generate plasma in the vicinity of the substrate. An atmosphere of nitrogen, helium, oxygen or the like may be applied instead of the argon atmosphere.

Either dry etching or wet etching may be used for etching the oxide semiconductor layer. Of course, De also be used in combination both as possible. Etching conditions (etching gas, etching solution, etching time, temperature, etc.) are appropriately set according to the material so that the oxide semiconductor layer can be etched into a desired shape.

As the dry etching, a parallel plate type RIE (Reactive Ion Etching) method, an ICP (Inductively Coupled Plasma) etching method, or the like can be used. Also in this case, it is necessary to appropriately set the etching conditions (the amount of power applied to the coil-type electrode, the amount of power applied to the electrode on the substrate side, the electrode temperature on the substrate side, etc.).

Etching gas that can be used for dry etching includes, for example, a gas containing chlorine (chlorine-based gas, for example, chlorine (Cl).₂), Boron trichloride (BCl)₃), Silicon tetrachloride (SiCl)₄), Carbon tetrachloride (CCl₄) Etc.) and so on. In addition, a gas containing fluorine (fluorine-based gas, for example, carbon tetrafluoride (CF)₄), Sulfur hexafluoride (SF₆), Nitrogen trifluoride (NF₃), Trifluoromethane (CHF)₃) Etc.), hydrogen bromide (HBr), oxygen (O₂), A gas obtained by adding a rare gas such as helium (He) or argon (Ar) to these gases may be used.

Etching solutions that can be used for wet etching include a solution in which phosphoric acid, acetic acid, and nitric acid are mixed, and ammonia superwater (a mixture of ammonia, water, and hydrogen peroxide solution). Further, an etching solution such as ITO07N (manufactured by Kanto Chemical Co., Inc.) may be used.

Next, it is desirable to perform the first heat treatment on the oxide semiconductor layer. Water (including hydroxyl groups), hydrogen, and the like in the oxide semiconductor layer can be removed by this first heat treatment. The temperature of the first heat treatment is 300 ° C or more and 800 ° C or less, preferably 400 ° C or more and 700 ° C or less, more preferably 450 ° C or more and 700 ° C or less, and more preferably 550 ° C or more and 700 ° C or less. It can be as follows.

By setting the temperature of the first heat treatment to 350 ° C. or higher, the oxide semiconductor layer can be dehydrated or dehydrogenated, and the hydrogen concentration in the oxide semiconductor layer can be reduced. Further, by setting the temperature of the first heat treatment to 450 ° C. or higher, the hydrogen concentration in the oxide semiconductor layer can be further reduced. Further, by setting the temperature of the first heat treatment to 550 ° C. or higher, the hydrogen concentration in the oxide semiconductor layer can be further reduced. For example, the substrate is introduced into an electric furnace using a resistance heating element or the like, and the oxide semiconductor layer 140 is heat-treated at 450 ° C. for 1 hour under a nitrogen atmosphere. During this period, the oxide semiconductor layer 140 is kept out of contact with the atmosphere to prevent water and hydrogen from being mixed.

The heat treatment apparatus is not limited to the electric furnace, and may be an apparatus that heats the object to be processed by heat conduction from a medium such as heated gas or heat radiation. For example, an RTA (Rapid Thermal Anneal) device such as a GRTA (Gas Rapid Thermal Anneal) device or an LRTA (Lamp Rapid Thermal Anneal) device can be used.

The LRTA device is a device that heats an object to be processed by radiating light (electromagnetic waves) emitted from lamps such as halogen lamps, metal halide lamps, xenon arc lamps, carbon arc lamps, high-pressure sodium lamps, and high-pressure mercury lamps. The GRTA device is a device that performs heat treatment using a high-temperature gas. As the gas, a rare gas such as argon or an inert gas such as nitrogen that does not react with the object to be treated by heat treatment is used.

For example, as the first heat treatment, a GRTA treatment is performed in which the substrate is placed in an inert gas atmosphere heated to a high temperature of 650 ° C to 700 ° C, heated for several minutes, and then the substrate is taken out from the inert gas atmosphere. You may. The GRTA treatment enables high temperature heat treatment in a short time. Further, since the heat treatment is performed for a short time, it can be applied even under temperature conditions exceeding the heat resistant temperature of the substrate. For example, when an SOI substrate containing a substrate having relatively low heat resistance such as a glass substrate is used, shrinkage of the substrate becomes a problem at a temperature exceeding the heat resistant temperature (distortion point), but in the case of short-time heat treatment, this is a problem. It doesn't matter.

As the inert gas atmosphere in which the first heat treatment is performed, an atmosphere containing nitrogen or a rare gas (helium, neon, argon, etc.) as a main component and not containing water, hydrogen, etc. is applied. Is desirable. For example, the purity of nitrogen and rare gases such as helium, neon, and argon to be introduced into the heat treatment equipment is 6N (99.9999%) or more, preferably 7N (99.99999%) or more (that is, the impurity concentration is 1ppm or less, preferably 0.1. ppm or less).

During the treatment, the atmosphere of the inert gas may be switched to an atmosphere containing oxygen. For example, when an electric furnace is used for the first heat treatment, the atmosphere can be switched when the temperature of the heat treatment is lowered. For example, the atmosphere during heat treatment (constant temperature) can be an inert gas atmosphere such as nitrogen or a rare gas (helium, neon, argon, etc.), and can be switched to an atmosphere containing oxygen when the temperature is lowered. As the atmosphere containing oxygen, oxygen gas or a gas obtained by mixing oxygen gas and nitrogen gas can be used.

Even when this oxygen-containing atmosphere is used, it is preferable that the atmosphere does not contain water, hydrogen, or the like. Alternatively, the purity of the oxygen gas and nitrogen gas used is preferably 6N (99.9999%) or more, preferably 7N (99.99999%) or more (that is, the impurity concentration is 1ppm or less, preferably 0.1ppm or less). By performing the first heat treatment in an atmosphere containing oxygen, defects caused by oxygen deficiency can be reduced.

Depending on the conditions of the first heat treatment or the material constituting the oxide semiconductor layer, the oxide semiconductor layer may crystallize into microcrystals or polycrystals. For example, it may be a microcrystalline oxide semiconductor layer having a crystallization rate of 90% or more, or 80% or more. Further, depending on the conditions of the first heat treatment or the material constituting the oxide semiconductor layer, an amorphous oxide semiconductor layer containing no crystal component may be obtained.

Further, in the case of an oxide semiconductor layer in which fine crystals (particle size 1 nm or more and 20 nm or less (typically 2 nm or more and 4 nm or less)) are mixed in an amorphous oxide semiconductor (for example, the surface of the oxide semiconductor layer). There is also. In this way, it is possible to change the electrical characteristics of the oxide semiconductor layer by mixing and arranging microcrystals in amorphous.

For example, when an oxide semiconductor layer is formed using an In-Ga-Zn-O-based metal oxide target, In has electrical anisotropy.₂Ga₂ZnO₇By forming a microcrystal region in which the crystal grains of the above are oriented, the electrical characteristics of the oxide semiconductor layer can be changed. The microcrystal region is, for example, In₂Ga₂ZnO₇It is preferable that the region is oriented so that the c-axis of the crystal is oriented perpendicular to the surface of the oxide semiconductor layer.

By forming the region in which the crystal grains are oriented in this way, the conductivity in the direction parallel to the surface of the oxide semiconductor layer is improved, and the insulating property in the direction perpendicular to the surface of the oxide semiconductor layer is improved. Can be done. Further, such a microcrystal region has a function of suppressing the invasion of impurities such as water and hydrogen into the oxide semiconductor layer.

The oxide semiconductor layer having the above-mentioned microcrystalline region can be formed by surface heating of the oxide semiconductor layer by GRTA treatment. Further, it can be more preferably formed by using a sputtering target having a Zn content smaller than that of In or Ga.

The first heat treatment on the oxide semiconductor layer 140 can also be performed on the oxide semiconductor layer before being processed into the island-shaped oxide semiconductor layer 140. In that case, after the first heat treatment, the substrate is taken out from the heating device and a photolithography step is performed.

The first heat treatment can also be called a dehydration treatment, a dehydrogenation treatment, or the like. In the dehydration treatment and dehydrogenation treatment, after the oxide semiconductor layer was formed, the source electrode or drain electrode was laminated on the oxide semiconductor layer 140, and then the gate insulating layer was formed on the source electrode or drain electrode. It can be done at a later timing such as. Further, such dehydration treatment and dehydrogenation treatment may be performed not only once but also a plurality of times.

Next, the conductive layer 142 is formed so as to be in contact with the oxide semiconductor layer 140, and then the insulating layer 164 is formed on the conductive layer 142 (see FIG. 17 (C)). The insulating layer 164 does not have to be formed.

The conductive layer 142 can be formed by using a PVD method such as a sputtering method or a CVD method such as a plasma CVD method. Further, the conductive layer 142 can be formed by using an element selected from aluminum, chromium, copper, tantalum, titanium, molybdenum, and tungsten, an alloy containing the above-mentioned element as a component, and the like. Materials containing any one or more of manganese, magnesium, zirconium, beryllium and yttrium may be used. Further, a material containing one or more elements selected from titanium, tantalum, tungsten, molybdenum, chromium, neodymium, and scandium in aluminum may be used.

Further, the conductive layer 142 may be formed by using a conductive metal oxide. Indium oxide (In) is a conductive metal oxide.₂O₃), Tin oxide (SnO)₂), Zinc oxide (ZnO), Indium tin oxide alloy (In₂O₃SnO₂, Sometimes abbreviated as ITO), Indium tin oxide alloy (In₂O₃-ZnO), or those in which silicon or silicon oxide is contained in these metal oxide materials can be used.

The conductive layer 142 may have a single-layer structure or a laminated structure of two or more layers. Examples thereof include a single-layer structure of an aluminum film containing silicon, a two-layer structure in which a titanium film is laminated on an aluminum film, and a three-layer structure in which a titanium film, an aluminum film, and a titanium film are laminated. Here, a three-layer structure of a titanium film, an aluminum film, and a titanium film is applied.

An oxide conductor layer may be formed between the oxide semiconductor layer 140 and the conductive layer 142. The oxide conductor layer and the conductive layer 142 can be continuously formed (continuous film formation). By providing such an oxide conductive layer, it is possible to reduce the resistance of the source region or the drain region, so that high-speed operation of the transistor is realized.

The insulating layer 164 can be formed by using a CVD method, a sputtering method, or the like. Further, the insulating layer 164 is preferably formed so as to contain silicon oxide, silicon nitride, silicon oxide nitride, silicon nitride oxide, aluminum oxide, hafnium oxide, tantalum oxide and the like. The insulating layer 164 may have a single-layer structure or a laminated structure. The thickness of the insulating layer 164 is not particularly limited, but may be, for example, 10 nm or more and 500 nm or less.

Next, the conductive layer 142 and the insulating layer 164 are selectively etched to form the source electrode or drain electrode 142a, the source electrode or drain electrode 142b, the insulating layer 164a, and the insulating layer 164b (see FIG. 17 (D)). ..

It is preferable to use ultraviolet rays, KrF laser light, or ArF laser light for exposure at the time of forming a mask used for etching. In particular, when performing exposure with a channel length (L) of less than 25 nm, it is preferable to perform mask-forming exposure using Extreme Ultraviolet, which has an extremely short wavelength of several nm to several tens of nm. is there. Exposure with ultra-ultraviolet rays has a high resolution and a large depth of focus. Therefore, it is possible to design so that the channel length (L) of the transistor formed later is less than 25 nm, that is, the channel length (L) can be 10 nm or more and 1000 nm or less. By reducing the channel length in this way, the operating speed can be improved. Further, since the transistor using the oxide semiconductor has a small off-current, it is possible to suppress an increase in power consumption due to miniaturization.

When etching the conductive layer 142, the respective materials and etching conditions are appropriately adjusted so that the oxide semiconductor layer 140 is not removed. Depending on the material and the etching conditions, a part of the oxide semiconductor layer 140 may be etched to form an oxide semiconductor layer having grooves (recesses) in the process.

Further, in order to reduce the number of times the mask is used and the number of steps, a resist mask may be formed by a multi-gradation mask which is an exposure mask in which transmitted light has a plurality of intensities, and an etching step may be performed using this. .. The resist mask formed by using the multi-gradation mask has a shape having a plurality of thicknesses (stepped shape) and can be further deformed by ashing, so that it can be used in a plurality of etching steps. That is, one multi-tone mask can form a resist mask corresponding to at least two or more different patterns. Therefore, the number of exposure masks can be reduced, and the corresponding photolithography process can also be reduced, so that the process can be simplified.

Next, the gate insulating layer 166 is formed in contact with a part of the oxide semiconductor layer 140 without being exposed to the atmosphere (see FIG. 17 (E)). The gate insulating layer 166 can be formed by using a CVD method, a sputtering method, or the like. Further, the gate insulating layer 166 is preferably formed so as to contain silicon oxide, silicon nitride, silicon oxide, silicon nitride oxide, aluminum oxide, hafnium oxide, tantalum oxide and the like. The gate insulating layer 166 may have a single-layer structure or a laminated structure. The thickness of the gate insulating layer 166 is not particularly limited, but may be, for example, 10 nm or more and 500 nm or less.

It should be noted that an oxide semiconductor (highly purified oxide semiconductor) that has been i-shaped or substantially i-shaped by removing impurities is extremely sensitive to interface states and interfacial charges. , High quality is required for the gate insulating layer 166.

For example, a high-density plasma CVD method using microwaves (for example, a frequency of 2.45 GHz) is suitable in that a high-quality gate insulating layer 166 that is dense and has a high dielectric strength can be formed. This is because the high-purity oxide semiconductor layer and the high-quality gate insulating layer are in close contact with each other, so that the interface state can be reduced and the interface characteristics can be improved.

Of course, if a high-quality insulating layer can be formed as the gate insulating layer 166, other methods such as a sputtering method and a plasma CVD method can be applied. Further, an insulating layer whose film quality, interface characteristics and the like are modified by heat treatment after formation may be applied. In any case, it suffices to provide a gate insulating layer 166 having a good film quality, a reduced interface level density with the oxide semiconductor layer, and a layer capable of forming a good interface.

By improving the interface characteristics with the gate insulating layer and eliminating impurities in the oxide semiconductor, especially hydrogen and water, the gate bias / thermal stress test (BT test: for example, 85 ° C, 2) × 10⁶It is possible to obtain a stable transistor whose threshold voltage (Vth) does not fluctuate with respect to V / cm, 12 hours, etc.).

Then, the second heat treatment is performed under an inert gas atmosphere or an oxygen atmosphere. The heat treatment temperature is 200 ° C or higher and 400 ° C or lower, preferably 250 ° C or higher and 350 ° C or lower. For example, heat treatment may be performed at 250 ° C. for 1 hour in a nitrogen atmosphere. When the second heat treatment is performed, the variation in the electrical characteristics of the transistor can be reduced. In the present embodiment, the second heat treatment is performed after the formation of the gate insulating layer 166, but the timing of the second heat treatment is not particularly limited as long as it is after the first heat treatment.

Next, the gate electrode 178 is formed in the region on the gate insulating layer 166 that overlaps with the oxide semiconductor layer 140 (see FIG. 18 (A)). The gate electrode 178 can be formed by forming a conductive layer on the gate insulating layer 166 and then selectively patterning the conductive layer.

The conductive layer can be formed by using a PVD method such as a sputtering method or a CVD method such as a plasma CVD method. Further, the conductive layer can be formed by using an element selected from aluminum, chromium, copper, tantalum, titanium, molybdenum, and tungsten, an alloy containing the above-mentioned element as a component, and the like. Materials containing any one or more of manganese, magnesium, zirconium, beryllium and yttrium may be used. Further, a material containing one or more elements selected from titanium, tantalum, tungsten, molybdenum, chromium, neodymium, and scandium in aluminum may be used.

Further, the conductive layer may be formed by using a conductive metal oxide. Indium oxide (In) is a conductive metal oxide.₂O₃), Tin oxide (SnO)₂), Zinc oxide (ZnO), Indium tin oxide alloy (In₂O₃SnO₂, Sometimes abbreviated as ITO), Indium tin oxide alloy (In₂O₃-ZnO), or those in which silicon or silicon oxide is contained in these metal oxide materials can be used.

The conductive layer may have a single-layer structure or a laminated structure of two or more layers. Examples thereof include a single-layer structure of an aluminum film containing silicon, a two-layer structure in which a titanium film is laminated on an aluminum film, and a three-layer structure in which a titanium film, an aluminum film, and a titanium film are laminated. Here, a conductive layer is formed using a material containing titanium, and the gate electrode 178 is processed.

Next, the interlayer insulating layer 170 and the interlayer insulating layer 172 are formed on the gate insulating layer 166 and the gate electrode 178 (see FIG. 18 (B)). The interlayer insulating layer 170 and the interlayer insulating layer 172 can be formed by using a PVD method, a CVD method, or the like. Further, it can be formed by using a material containing an inorganic insulating material such as silicon oxide, silicon nitride oxide, silicon nitride, hafnium oxide, aluminum oxide, and tantalum oxide. In the present embodiment, the interlayer insulating layer 170 and the interlayer insulating layer 172 are laminated, but one aspect of the disclosed invention is not limited to this. It may be one layer or a laminated structure of three or more layers.

It is desirable that the interlayer insulating layer 172 is formed so that its surface is flat. This is because by forming the interlayer insulating layer 172 so that the surface becomes flat, electrodes, wiring, and the like can be suitably formed on the interlayer insulating layer 172.

Next, openings are formed in the gate insulating layer 166, the interlayer insulating layer 170, and the interlayer insulating layer 172 to reach the electrode 136a, the electrode 136b, the electrode 136c, the source electrode or the drain electrode 142a, and the source electrode or the drain electrode 142b. A conductive layer is formed so as to be embedded in the opening. Then, a part of the conductive layer is removed by a method such as etching or CMP to expose the interlayer insulating layer 172 to form an electrode 154a, an electrode 154b, an electrode 154c, an electrode 154d, and an electrode 154e (FIG. 18 (FIG. 18). See C)).

The opening can be formed by a method such as etching using a mask. The mask can be formed by a method such as exposure using a photomask. Either wet etching or dry etching may be used as the etching, but from the viewpoint of microfabrication, it is preferable to use dry etching.

The conductive layer can be formed by using a PVD method, a CVD method, or the like. Examples of the material that can be used for forming the conductive layer include conductive materials such as molybdenum, titanium, chromium, tantalum, tungsten, aluminum, copper, neodymium, and scandium, and alloys and compounds (for example, nitrides) thereof. Be done.

Specifically, for example, a method of forming a thin titanium film by the PVD method in a region including an opening, forming a thin titanium nitride film by the CVD method, and then forming a tungsten film so as to be embedded in the opening can be applied. it can. Here, the titanium film formed by the PVD method is an oxidation that can be formed on the surface of a lower electrode (here, an electrode 136a, an electrode 136b, an electrode 136c, a source electrode or a drain electrode 142a, a source electrode or a drain electrode 142b, etc.). It has the function of reducing the film and reducing the contact resistance with the lower electrode. Further, the titanium nitride formed thereafter has a barrier function of suppressing the diffusion of the conductive material. Further, after forming a barrier film made of titanium, titanium nitride or the like, a copper film may be formed by a plating method. The dual damascene method may be applied as well as the so-called single damascene method.

When removing a part of the conductive layer, it is desirable to process the surface of the exposed interlayer insulating layer 172 so that the surfaces of the electrodes 154a, 154b, electrodes 154c, electrodes 154d, and electrodes 154e are flat. .. By flattening the surface in this way, it becomes possible to form good electrodes, wiring, and the like in a later process.

After that, an insulating layer 156 is further formed, an opening reaching the electrode 154a, an electrode 154b, an electrode 154c, an electrode 154d, and an electrode 154e is formed in the insulating layer 156, and a conductive layer is formed so as to be embedded in the opening. A part of the conductive layer is removed by a method such as etching or CMP to expose the insulating layer 156 to form electrodes 158a, 158b, electrodes 158c, and electrodes 158d (see FIG. 18 (D)). Since the step is the same as the case of forming the electrode 154a and the like, the details will be omitted.

When the transistor 402 is manufactured by the above method, the hydrogen concentration of the oxide semiconductor layer 140 is 5 × 10.¹⁹/cm³The off current of the transistor 402 is 1 × 10.^-13It becomes A or less. As described above, by applying the oxide semiconductor layer 140 in which the hydrogen concentration is sufficiently reduced, oxygen is supplied, and the purity is increased, the transistor 402 having excellent characteristics can be obtained.

If oxygen is supplied to the oxide semiconductor layer 140 immediately after the hydrogen concentration is reduced, there is no risk of hydrogen or water being mixed into the oxide semiconductor layer, so that the oxide semiconductor has extremely good characteristics. It is preferable in that a layer can be realized. Of course, if the oxide semiconductor layer having good characteristics can be realized, the hydrogen concentration reduction treatment and the oxygen supply treatment do not need to be continuously performed. For example, another process may be included between these processes. Further, these processes may be performed at the same time.

Further, since the lower part has a transistor 160 using a material other than an oxide semiconductor and the upper part has a transistor 402 using an oxide semiconductor, a non-volatile latch circuit having excellent characteristics having both characteristics and a non-volatile latch circuit thereof are provided. The semiconductor device used can be manufactured.

In oxide semiconductors, many studies on physical properties such as DOS (density of state) have been carried out, but these studies do not include the idea of sufficiently reducing the localized level itself. In one aspect of the disclosed invention, a highly purified oxide semiconductor is produced by removing water and hydrogen, which may cause a localized level, from the oxide semiconductor. This is based on the idea of sufficiently reducing the localized level itself. And this makes it possible to manufacture extremely excellent industrial products.

When removing hydrogen, water, etc., oxygen may be removed at the same time. Therefore, by supplying oxygen to the unpaired bond of the metal generated by oxygen deficiency and reducing the localization level due to oxygen defects, the oxide semiconductor is further purified (i-typed). Is suitable. For example, by forming an oxygen-excessive oxide film in close contact with the channel formation region and performing heat treatment under temperature conditions of 200 ° C to 400 ° C, typically about 250 ° C, oxygen can be obtained from the oxide film. Can be supplied to reduce localization levels due to oxygen defects. Further, during the second heat treatment, the inert gas may be switched to a gas containing oxygen. It is also possible to supply oxygen to the oxide semiconductor by undergoing a temperature lowering process in an oxygen atmosphere or an atmosphere in which hydrogen and water are sufficiently removed following the second heat treatment.

Factors that deteriorate the characteristics of oxide semiconductors are considered to be due to shallow levels of 0.1 to 0.2 eV under the conduction band due to excess hydrogen and deep levels due to oxygen deficiency. In order to eliminate these defects, the technical idea of thoroughly removing hydrogen and supplying sufficient oxygen would be correct.

Oxide semiconductors are generally considered to be n-type, but in one aspect of the disclosed invention, impurities such as water and hydrogen are removed, and oxygen, which is a constituent element of the oxide semiconductor, is supplied to form i-type. Achieve the conversion. In this respect, it can be said that it includes an unprecedented technical idea rather than the i-type by adding impurities like silicon.

By using a non-volatile latch circuit that uses a transistor that uses an oxide semiconductor as the semiconductor material that constitutes the channel formation region according to this embodiment as a switching element of the data holding unit, the temperature operating range is wide and even at high temperatures. It is possible to realize a non-volatile latch circuit that operates stably and does not erase the stored logical state even when the power is turned off, or a latch circuit that incorporates a data holding unit having a sufficiently long refresh period. Since data is written by switching transistors, there is virtually no limit to the number of rewrites. Further, the write voltage is about the threshold voltage of the transistor, and it is possible to operate at a low voltage. Further, since the potential of the data holding unit is directly applied, the variation in the amount of charge held as data can be suppressed to be small, and the data can be easily read out.

By using the non-volatile latch circuit, various logic circuits can be realized. For example, power consumption can be reduced by turning off the power of unused blocks. In addition, since the logical state is memorized even when the power is turned off, it is possible to start the system when the power is turned on and shut down the system when the power is turned off at high speed and with low power consumption. Is.

As described above, the configurations and methods shown in the present embodiment can be appropriately combined with the configurations and methods shown in other embodiments.

(Embodiment 3) In the present embodiment, the configuration and operation of a non-volatile latch circuit, which is one aspect of the disclosed invention, will be described with reference to FIG.

FIG. 19A shows the configuration of the non-volatile latch circuit 400 having the latch portion 411 and the data holding portion 401 for holding the data of the latch portion. FIG. 19B shows an example of a timing chart of the non-volatile latch circuit 400.

FIG. 19A is an example in which the configuration of the latch portion 411 in FIG. 1 is specifically shown. FIG. 19A shows an example in which the inverter 412 is used as the first element and the inverter 413 is used as the second element in the configuration of the latch portion 411 of FIG. The configuration of the transistor 402 can be the same as that of the first embodiment or the second embodiment.

The latch portion 411 has an inverter 412 and an inverter 413. It has a loop structure in which the output of the inverter 412 is electrically connected to the input of the inverter 413, and the output of the inverter 413 is electrically connected to the input of the inverter 412. Further, the latch portion 411 has a switch 431 and a switch 432, and the output of the inverter 413 is electrically connected to the input of the inverter 412 via the switch 432.

The input of the inverter 412 is electrically connected to the wiring 414 to which the input signal of the latch circuit is given via the switch 431. The output of the inverter 412 is electrically connected to the wiring 415 to which the output signal of the latch circuit is given. The node connected to the input of the inverter 412 will be called node P. The node P is electrically connected to the wiring 414 to which the input signal of the latch circuit is given. Node P is also a node that is electrically connected to the output of the inverter 413. The potential of the node P is the same as the potential of the input of the inverter 412.

The data holding unit 401 uses a transistor 402 that uses an oxide semiconductor as a semiconductor material constituting the channel forming region as a switching element. Further, it has a capacitance 404 electrically connected to the source electrode or the drain electrode of the transistor 402. One of the electrodes having a capacitance of 404 is electrically connected to one of the source electrode and the drain electrode of the transistor 402. The other of the source electrode and the drain electrode of the transistor is electrically connected to the input (node P) of the inverter 412 in the latch portion.

Further, the other of the source electrode and the drain electrode of the transistor is electrically connected to the wiring 414 to which the input signal of the latch circuit is given via the switch 431. The potential Vc is given to the other end of the electrode with a capacitance of 404. The node in which the transistor 402 and the capacitance 404 are electrically connected is called a node S.

The transistor 402 using this oxide semiconductor has a function of writing the data held in the latch unit 411 to the capacity 404 of the data holding unit 401. Further, the transistor 402 has a function of holding the data written in the capacity 404 of the data holding unit 401. Further, the transistor 402 has a function of reading the data held in the capacity 404 of the data holding unit 401 to the latch unit 411.

The potential of the input signal IN is given to the wiring 414 from the circuit in the previous stage. The potential of the wiring 415 is given to the subsequent circuit as an output signal OUT. The potential of the clock signal φ1 is given to the switch 431. When a high level potential is applied to the clock signal φ1, the switch 431 is turned on. The potential of the clock signal φ2 is given to the switch 432. When a high level potential is applied to the clock signal φ2, the switch 432 is turned on. Control signal φ at the gate of transistor 402_LSThe potential of is given. Control signal φ_LSWhen a high level potential is applied to the transistor 402, the transistor 402 is turned on. In the normal operation period, the clock signal φ2 has a signal obtained by inverting the clock signal φ1. Here, an example is shown in which the transistor and the switch are turned on when the control signal and the clock signal are at a high level.

A high-level power supply voltage VDD and a low-level power supply voltage VSS are given to the inverter 412 and the inverter 413 of the latch portion 411, respectively.

Next, as shown in FIG. 19 (B), the input signal IN, the output signal OUT, and the control signal φ during the period (operating period) and the stopped state (non-operating period) of the non-volatile latch circuit 400._LS, An example of the timing chart of the potentials of the clock signal φ1 and the clock signal φ2 is shown. Further, the potentials of the node S of the data holding unit 401, the node P of the latch unit 411, the inverter 412 of the latch unit 411, and the power supply voltage VDD-L of the inverter 413 are also shown. Node S shows the potential of one electrode of capacitance 404. A predetermined potential Vc is given to the other electrode having a capacity of 404. For example, a ground potential is given.

In FIG. 19B, period a, period b, period d, and period e are periods during which the latch circuit 400 is in an operating state (operating period), and period c is a period during which the latch circuit 400 is stopped (non-operating period). Is. The period a and the period e are normal operating periods of the latch circuit 400, and high-level or low-level potentials are alternately applied to the clock signal φ1 and the clock signal φ2. Period b is the preparatory period before the non-operation period. Period b is also called the start-up period. The period d is the preparation period after the non-operating period until the power is supplied and the normal operating period is entered. The period d is also called the start-up period.

During the normal operating period (period a), when a high-level potential is applied to the clock signal φ1 and a low-level potential is applied to the clock signal φ2, the switch 432 is turned off, the inverter loop is disconnected, and the switch 431 is turned on to input. The signal potential is input to the inverter 412. The potential of the input signal is inverted by the inverter 412 and given to the subsequent circuit as an output signal OUT. When a high level potential is applied to the clock signal φ1, if the potential of the input signal is high level, an output signal having a low level potential is obtained. When a high level potential is applied to the clock signal φ1, if the potential of the input signal is low level, an output signal having a high level potential can be obtained.

When a low-level potential is applied to the clock signal φ1 and a high-level potential is applied to the clock signal φ2, the switch 431 is turned off, the switch 432 is turned on, an inverter loop is formed, and the potential of the output signal OUT is maintained (data). Is latched, that is, the logical state of the latch circuit is preserved).

Control signal φ during normal operation period_LSIs given a potential to turn off the transistor 402, and is not given a potential to turn on the transistor 402. The node S has a potential corresponding to the charge previously held. Here, it is an indefinite value.

Next, in the preparation period (period b) before the non-operation period, the control signal φ_LSWhen the potential for turning on the transistor 402 is given to, the transistor 402 is turned on, and the potential of the input (node P) of the inverter 412 of the latch portion is given to the node S (write). If the potential of the input (node P) of the inverter 412 of the latch portion is high level, the potential of node S becomes high level. Charges corresponding to the electric potential are accumulated in the node S.

After that, the control signal φ_LSIs given a potential to turn off the transistor 402, the transistor 402 is turned off, and the node S is in a floating state. As a result, the charge accumulated in the node S is retained (retained) as it is.

In the period b, the clock signal φ2 and the clock signal φ1 may maintain the potential at the end of the period a. Alternatively, the clock signal φ2 may be fixed at a high level and the clock signal φ1 may be fixed at a low level, and the data at the end of the period a may be latched.

Next, during the non-operating period (period c), the power supply is stopped and the power supply voltage VDD-L drops. The clock signal φ1, the clock signal φ2, the input signal IN, and the output signal OUT may take any value between VDD and VSS. During this time, the control signal φ_LSThe potential of is held at a low level so that the transistor 402 is in the off state. For example, it is held at the ground potential. By turning off the transistor 402 during the non-operating period (period c), the electric charge accumulated in the node S is retained (retained).

Next, after the non-operating period, in the preparation period (period d) until the normal operating period starts, power is supplied, and the clock signal φ2 and the clock signal φ1 are fixed at a low level. The potentials of the node P and the output signal OUT depend on the potential of the node P before power is supplied, the potential of the output signal OUT, etc., but here, the node P is at a low level and the output signal OUT is at a high level. And.

And the control signal φ_LSWhen the potential for turning on the transistor 402 is given to the transistor 402, the potential for turning on the transistor 402 is given to the latch portion 411. Specifically, the electric charge is distributed between the node S and the input of the inverter 412 (node P), and the input of the inverter 412 (node P) is given a potential corresponding to the electric charge accumulated in the node S. Here, the electric charge accumulated in the node S is distributed to the latch portion 411, the potential of the input (node P) of the inverter 412 rises, and the potential of the node S decreases slightly. As a result, the potential of the input (node P) of the inverter 412 and the potential of the node S become substantially high-level potentials.

Then, the potential of the node P in the latch portion is inverted by the inverter 412 and given to the subsequent circuit as an output signal OUT. Here, an example is shown in which the potential held in the node S and the potential given to the node P in the latch portion are at a high level, and an output signal having a low level potential can be obtained. As a result, the logical state of the latch circuit can be returned to the logical state before entering the non-operating period.

After that, the control signal φ_LSIs given a potential to turn off the transistor 402, the transistor 402 is turned off, and the node S is in a floating state. As a result, the charge accumulated in the node S is retained (retained) as it is. The charge accumulated in the node S is then the control signal φ_LSIt is rewritten at the timing when the potential for turning on the transistor 402 is given to. Therefore, next, the control signal φ_LSThe charge accumulated in the node S is retained as it is until the timing when the potential for turning on the transistor 402 is given to the node S.

Further, in the period d, the control signal φ_LSAfter the potential for turning on the transistor 402 is given to the clock signal φ2, a period for setting the clock signal φ2 to a high level may be provided. When a high level potential is applied to the clock signal φ2, the switch 432 is turned on and an inverter loop is formed. When the inverter loop is formed, the output signal OUT and node P are given high or low level potentials and held (data latched).

As described above, the data reading to the latch portion is performed by the distribution of electric charges between the node S and the input (node P) of the inverter 412. When the electric charge corresponding to the high level potential is accumulated in the node S, the input of the inverter S and the inverter 412 (node) does not depend on the potential of the input of the inverter 412 (node P) before the transistor 402 is turned on. The potential of the input (node P) of the inverter 412 after the charge is distributed to P) is set to be higher than the threshold value of the inverter 412 (the input potential at which the output of the inverter is inverted).

Further, when the electric charge corresponding to the low level potential is accumulated in the node S, the input of the node S and the inverter 412 is not affected by the potential of the input of the inverter 412 (node P) before the transistor 402 is turned on. The potential of the input (node P) of the inverter 412 after the charge is distributed to (node P) is set to be lower than the threshold value of the inverter 412 (the input potential at which the output of the inverter is inverted).

In order to do so, for example, it is preferable that the capacity of the node S is larger than the capacity of the node P. That is, it is preferable that the capacity value of the capacity 404 electrically connected to the node S is larger than the capacity value of the input capacity (gate capacity of the transistor of the inverter) of the inverter 412 electrically connected to the node P. It is also effective to set a period in which the potential Vc is a value between VDD and VSS in the period d. This makes it possible to perform the read operation more stably.

By doing so, it is possible to read data to the latch part not only when the node P is low level and the output signal OUT is high level, but also when the node P is high level and the output signal OUT is low level. It is possible. In addition, it is possible to read data to the latch portion not only when the electric charge corresponding to the high level potential is accumulated in the node S but also when the electric charge corresponding to the low level potential is accumulated in the node S. is there.

Next, high-level and low-level potentials are alternately applied to the clock signal φ1 and the clock signal φ2, resulting in a normal operating state (period e). At the start of the normal operating period (period e), the clock signal φ1 and the clock signal φ2 may start from the same potential (same state) as at the end of the previous normal operating period (period a). It may start from the potential (next state) reversed from the end of the period a.

By using a non-volatile latch circuit that uses a transistor that uses an oxide semiconductor as the semiconductor material that constitutes the channel formation region according to this embodiment as a switching element of the data holding unit, the temperature operating range is wide and even at high temperatures. It is possible to realize a non-volatile latch circuit that operates stably and does not erase the stored logical state even when the power is turned off, or a latch circuit that incorporates a data holding unit having a sufficiently long refresh period. Since data is written by switching transistors, there is virtually no limit to the number of rewrites. Further, the write voltage is about the threshold voltage of the transistor, and it is possible to operate at a low voltage. Further, since the potential of the data holding unit is directly applied, the variation in the amount of charge held as data can be suppressed to be small, and the data can be easily read out.

By using the non-volatile latch circuit, various logic circuits can be realized. For example, power consumption can be reduced by turning off the power of unused blocks. In addition, since the logical state is memorized even when the power is turned off, it is possible to start the system when the power is turned on and shut down the system when the power is turned off at high speed and with low power consumption. Is.

This embodiment can be freely combined with other embodiments.

(Embodiment 4) In the present embodiment, the operation of a non-volatile latch circuit, which is one aspect of the disclosed invention, will be described with reference to FIG. 20 (A). The configuration of the non-volatile latch circuit is the same as in FIG. 19 (A), and the timing chart shows an example different from that in FIG. 19 (B).

FIG. 20 (A) shows the input signal IN, the output signal OUT, and the control signal φ during the period (operating period) and the stopped state (non-operating period) of the non-volatile latch circuit 400._LS, An example of the timing chart of the potentials of the clock signal φ1 and the clock signal φ2 is shown. The potentials of the node S of the data holding unit 401, the node P of the latch unit 411, and the power supply voltage VDD-L are also shown. Node S shows the potential of one electrode of capacitance 404. A potential Vc is given to the other electrode having a capacity of 404.

In FIG. 20 (A), the period a, the period b, the period d, and the period e are the periods during which the latch circuit 400 is in the operating state (operating period), and the period c is the period during which the latch circuit 400 is stopped (non-operating period). Is. The period a and the period e are normal operating periods of the latch circuit 400, and high-level or low-level potentials are alternately applied to the clock signal φ1 and the clock signal φ2. Period b is the preparatory period before the non-operation period. Period b is also called the start-up period. The period d is the preparation period from the non-operating period to the start of the normal operating period. The period d is also called the start-up period.

In FIG. 20 (A), the operations of the period a, the period b, and the period c are the same as those in FIG. 19 (B). Next, after the non-operating period, the clock signal φ2 and the clock signal φ1 are fixed at a low level in the preparation period (period d) until the power is supplied and the normal operating period starts. The potentials of the node P and the output signal OUT depend on the potential of the node P before power is supplied, the potential of the output signal OUT, etc., but here, the node P is at a low level and the output signal OUT is at a high level. And.

And the control signal φ_LSWhen the potential for turning on the transistor 402 is given to the transistor 402, the potential for turning on the transistor 402 is given to the latch portion 411. Specifically, the electric charge is distributed between the node S and the input of the inverter 412 (node P), and the input of the inverter 412 (node P) is given a potential corresponding to the electric charge accumulated in the node S. Here, the electric charge accumulated in the node S is distributed to the latch portion 411, the potential of the input (node P) of the inverter 412 rises, and the potential of the node S decreases slightly.

As a result, the potential of the input (node P) of the inverter 412 and the potential of the node S become substantially high-level potentials. Then, the potential of the node P in the latch portion is inverted by the inverter 412 and given to the subsequent circuit as an output signal OUT. Here, an example is shown in which the potential held in the node S and the potential given to the node P in the latch portion are at a high level, and an output signal having a low level potential can be obtained. As a result, the logical state of the latch circuit can be returned to the logical state before entering the non-operating period.

Next, the control signal φ_LSA high-level potential is applied to the clock signal φ2 while the potential for turning on the transistor 402 is still applied to the clock signal φ2. When a high level potential is applied to the clock signal φ2, the switch 432 is turned on and an inverter loop is formed. When the inverter loop is formed, the output signal OUT and node P are given high or low level potentials and held (data latched).

In particular, even if the charge is distributed between the node S and the input of the inverter 412 (node P) and the input of the inverter 412 (node P) has a potential slightly deviated from the high level or the low level, the high level is renewed. Alternatively, a low level potential is supplied. Then, the potential of node P is given to node S. As a result, even if the node S has a potential slightly deviated from the high level or the low level, the high level or the low level potential is supplied again. As a result, the potential of the node S can be returned to the state before the fluctuation (also called rewriting).

After that, the control signal φ_LSIs given a potential to turn off the transistor 402, the transistor 402 is turned off, and the node S is in a floating state. As a result, the charge accumulated in the node S is retained (retained) as it is. The charge accumulated in the node S is then the control signal φ_LSIt is rewritten at the timing when the potential for turning on the transistor 402 is given to. Therefore, next, the control signal φ_LSThe charge accumulated in the node S is retained as it is until the timing when the potential for turning on the transistor 402 is given to the node S.

As described above, the data reading to the latch portion is performed by the distribution of electric charges between the node S and the input (node P) of the inverter 412. When the electric charge corresponding to the high level potential is accumulated in the node S, the input of the inverter S and the inverter 412 (node) does not depend on the potential of the input of the inverter 412 (node P) before the transistor 402 is turned on. The potential of the input (node P) of the inverter 412 after the charge is distributed to P) is set to be higher than the threshold value of the inverter 412 (the input potential at which the output of the inverter is inverted).

Further, when the electric charge corresponding to the low level potential is accumulated in the node S, the input of the node S and the inverter 412 is not affected by the potential of the input of the inverter 412 (node P) before the transistor 402 is turned on. The potential of the input (node P) of the inverter 412 after the charge is distributed to (node P) is set to be lower than the threshold value of the inverter 412 (the input potential at which the output of the inverter is inverted).

In order to do so, for example, it is preferable that the capacity of the node S is larger than the capacity of the node P. That is, it is preferable that the capacity value of the capacity 404 electrically connected to the node S is larger than the capacity value of the input capacity (gate capacity of the transistor of the inverter) of the inverter 412 electrically connected to the node P. It is also effective to set a period in which the potential Vc is a value between VDD and VSS in the period d. This makes it possible to perform the read operation more stably.

By doing so, it is possible to read data to the latch part not only when the node P is low level and the output signal OUT is high level, but also when the node P is high level and the output signal OUT is low level. It is possible. In addition, it is possible to read data to the latch portion not only when the electric charge corresponding to the high level potential is accumulated in the node S but also when the electric charge corresponding to the low level potential is accumulated in the node S. is there.

Next, high-level and low-level potentials are alternately applied to the clock signal φ1 and the clock signal φ2, resulting in a normal operating state (period e). At the start of the normal operating period (period e), the clock signal φ1 and the clock signal φ2 may start from the same potential (same state) as at the end of the previous normal operating period (period a). It may start from the potential (next state) reversed from the end of the period a.

By using a non-volatile latch circuit that uses a transistor that uses an oxide semiconductor as the semiconductor material that constitutes the channel formation region according to this embodiment as a switching element of the data holding unit, the temperature operating range is wide and even at high temperatures. It is possible to realize a non-volatile latch circuit that operates stably and does not erase the stored logical state even when the power is turned off, or a latch circuit that incorporates a data holding unit having a sufficiently long refresh period.

Further, since data is written by switching transistors, there is substantially no limit to the number of rewrites. Further, the write voltage is about the threshold voltage of the transistor, and it is possible to operate at a low voltage. Further, since the potential of the data holding unit is directly applied, the variation in the amount of charge held as data can be suppressed to be small, and the data can be easily read out.

By using the non-volatile latch circuit, various logic circuits can be realized. For example, power consumption can be reduced by turning off the power of unused blocks. In addition, since the logical state is memorized even when the power is turned off, it is possible to start the system when the power is turned on and shut down the system when the power is turned off at high speed and with low power consumption. Is.

This embodiment can be freely combined with other embodiments.

(Embodiment 5) In the present embodiment, the operation of a non-volatile latch circuit, which is one aspect of the disclosed invention, will be described with reference to FIG. 20 (B). The configuration of the non-volatile latch circuit is the same as in FIG. 19 (A), and the timing chart shows an example different from those in FIGS. 19 (B) and 20 (A).

FIG. 20B shows the input signal IN, the output signal OUT, and the control signal φ during the period in which the non-volatile latch circuit 400 is in the operating state (operating period) and the stopped state (non-operating period)._LS, An example of the timing chart of the potentials of the clock signal φ1 and the clock signal φ2 is shown. Further, the node S of the data holding unit 401, the node P of the latch unit 411, the potential of the power supply voltage VDD-L, and the potential Vc of the other electrode of the capacitance 404 are also shown. Node S shows the potential of one electrode of capacitance 404.

In FIG. 20B, period a, period b, period d, and period e are periods during which the latch circuit 400 is in an operating state (operating period), and period c is a period during which the latch circuit 400 is stopped (non-operating period). Is. The period a and the period e are normal operating periods of the latch circuit 400, and high-level or low-level potentials are alternately applied to the clock signal φ1 and the clock signal φ2. Period b is the preparatory period before the non-operation period. Period b is also called the start-up period. The period d is the preparation period after the non-operating period until the power is supplied and the normal operating period is entered. The period d is also called the start-up period.

In FIG. 20 (B), the operations of the period a, the period b, and the period c are the same as those in FIG. 19 (B). Next, after the non-operating period, in the preparation period (period d) until the normal operating period starts, power is supplied, and the clock signal φ2 and the clock signal φ1 are fixed at a low level. The potentials of the node P and the output signal OUT depend on the potential of the node P before power is supplied, the potential of the output signal OUT, etc., but here, the node P is at a low level and the output signal OUT is at a high level. And.

And the control signal φ_LSWhen the potential for turning on the transistor 402 is given to the transistor 402, the potential for turning on the transistor 402 is given to the latch portion 411. Specifically, the electric charge is distributed between the node S and the input (node P) of the inverter 412. And the control signal φ_LSAt the timing when the potential for turning on the transistor 402 is given to, a predetermined potential is given to the potential Vc of the other electrode of the capacitance. The potential Vc is raised from the low level potential to a potential between low and high levels.

As a result, the input (node P) of the inverter 412 is given a potential determined by the distribution of electric charge with the node S, plus an increment of the potential Vc of the other electrode of the capacitance. Here, the electric charge accumulated in the node S is distributed to the latch portion 411, and a predetermined potential is given to the potential Vc, so that the potential of the input (node P) of the inverter 412 rises and the potential of the node S. Decreases slightly. As a result, the potential of the input (node P) of the inverter 412 and the potential of the node S become substantially high-level potentials.

Then, the potential of the node P in the latch portion is inverted by the inverter 412 and given to the subsequent circuit as an output signal OUT. As a result, the logical state of the latch circuit can be returned to the logical state before entering the non-operating period. Then, the potential Vc of the other electrode of the capacitance is returned to a low level potential.

Next, the control signal φ_LSA high-level potential is applied to the clock signal φ2 while the potential for turning on the transistor 402 is still applied to the clock signal φ2. When a high level potential is applied to the clock signal φ2, the switch 432 is turned on and an inverter loop is formed. When the inverter loop is formed, high-level or low-level potential is applied to the output signal OUT and node P and held (data is latched).

In particular, even if the charge is distributed between the node S and the input of the inverter 412 (node P) and the input of the inverter 412 (node P) has a potential slightly deviated from the high level or the low level, the high level is renewed. Alternatively, a low level potential is supplied. Then, the potential of node P is given to node S. As a result, even if the node S has a potential slightly deviated from the high level or the low level, the high level or the low level potential is supplied again. As a result, the potential of the node S can be returned to the state before the fluctuation (also called rewriting).

After that, the control signal φ_LSIs given a potential to turn off the transistor 402, the transistor 402 is turned off, and the node S is in a floating state. As a result, the charge accumulated in the node S is retained (retained) as it is. The charge accumulated in the node S is then the control signal φ_LSIt is rewritten at the timing when the potential for turning on the transistor 402 is given to. Therefore, next, the control signal φ_LSThe charge accumulated in the node S is retained as it is until the timing when the potential for turning on the transistor 402 is given to the node S.

As described above, the data reading to the latch portion is performed by distributing the electric charge between the node S and the input of the inverter 412 (node P) and controlling the potential Vc. When the electric charge corresponding to the high level potential is accumulated in the node S, the input of the inverter S and the inverter 412 (node) does not depend on the potential of the input of the inverter 412 (node P) before the transistor 402 is turned on. The potential of the input (node P) of the inverter 412 after the charge is distributed to P) is set to be higher than the threshold value of the inverter 412 (the input potential at which the output of the inverter is inverted).

Further, when the electric charge corresponding to the low level potential is accumulated in the node S, the input of the node S and the inverter 412 is not affected by the potential of the input of the inverter 412 (node P) before the transistor 402 is turned on. The potential of the input (node P) of the inverter 412 after the charge is distributed to (node P) is set to be lower than the threshold value of the inverter 412 (the input potential at which the output of the inverter is inverted).

In order to do so, for example, it is preferable that the capacity of the node S is larger than the capacity of the node P. That is, it is preferable that the capacity value of the capacity 404 electrically connected to the node S is larger than the capacity value of the input capacity (gate capacity of the transistor of the inverter) of the inverter 412 electrically connected to the node P. It is also effective to set a period in which the potential Vc is a value between VDD and VSS in the period d. This makes it possible to perform the read operation more stably.

By doing so, it is possible to read data to the latch part not only when the node P is low level and the output signal OUT is high level, but also when the node P is high level and the output signal OUT is low level. It is possible. In addition, it is possible to read data to the latch portion not only when the electric charge corresponding to the high level potential is accumulated in the node S but also when the electric charge corresponding to the low level potential is accumulated in the node S. is there.

In particular, as described in this embodiment, the control signal φ_LSBy applying a predetermined potential to the potential Vc of the other electrode of the capacitance at the timing when the potential at which the transistor 402 is turned on is given to, the reading can be performed more stably.

For example, when the capacity value of the capacity 404 is small or when the power supply is stopped for a long period of time, the potential of the input (node P) of the inverter 412 after charge distribution and the threshold value of the inverter 412 (inverter output). It becomes difficult to maintain the magnitude relationship with the input potential at which is inverted, and the read stability may decrease.

Even in such a case, by applying a predetermined potential to the potential Vc of the other electrode of the capacitance, it is possible to maintain the magnitude relationship of the above-mentioned potentials and control so as to keep the potential difference as large as possible. .. As a result, stable reading can be performed. That is, it is possible to operate even with a capacity having a smaller capacity value, and it is possible to reduce the size. Alternatively, the data retention period can be extended.

The timing of returning the potential Vc of the other electrode of the capacitance to the low level potential may be after the high level potential is applied to the clock signal φ2. Control signal φ_LSThe potential may be returned to the low level before the potential for turning off the transistor 402 is given to.

Next, high-level and low-level potentials are alternately applied to the clock signal φ1 and the clock signal φ2, resulting in a normal operating state (period e). At the start of the normal operating period (period e), the clock signal φ1 and the clock signal φ2 may start from the same potential (same state) as at the end of the previous normal operating period (period a). It may start from the potential (next state) reversed from the end of the period a.

By using a non-volatile latch circuit that uses a transistor that uses an oxide semiconductor as the semiconductor material that constitutes the channel formation region according to this embodiment as a switching element of the data holding unit, the temperature operating range is wide and even at high temperatures. It is possible to realize a non-volatile latch circuit that operates stably and does not erase the stored logical state even when the power is turned off, or a latch circuit that incorporates a data holding unit having a sufficiently long refresh period.

Further, since data is written by switching transistors, there is substantially no limit to the number of rewrites. Further, the write voltage is about the threshold voltage of the transistor, and it is possible to operate at a low voltage. Further, since the potential of the data holding unit is directly applied, the variation in the amount of charge held as data can be suppressed to be small, and the data can be easily read out. In addition, the capacity of the data holding unit can be made smaller, and the size can be reduced.

By using the non-volatile latch circuit, various logic circuits can be realized. For example, power consumption can be reduced by turning off the power of unused blocks. In addition, since the logical state is memorized even when the power is turned off, it is possible to start the system when the power is turned on and shut down the system when the power is turned off at high speed and with low power consumption. Is.

This embodiment can be freely combined with other embodiments.

(Embodiment 6) The present embodiment describes a configuration of a logic circuit having a plurality of non-volatile latch circuits, which is one aspect of the disclosed invention, with reference to FIG. 21.

FIG. 21 shows the configuration of a logic circuit having two non-volatile latch circuits 400 having a latch portion 411 and a data holding portion 401 for holding data in the latch portion. This logic circuit is called D-FF, and is used as a register in, for example, a CPU or various logic circuits.

The configuration of the data holding unit 401 is the same as that in FIG. The configuration of the latch portion 411 is an example in which the NAND is used as the first element and the clocked inverter is used as the second element in the configuration of the latch portion 411 of FIG.

The latch portion 411 has a NAND 412 and a clocked inverter 413. It has a loop structure in which the output of the NAND 412 is electrically connected to the input of the clocked inverter 413 and the output of the clocked inverter 413 is electrically connected to the input of the NAND 412. Further, the latch portion 411 has an analog switch 431.

One of the inputs of the NAND 412 is electrically connected via the analog switch 431 to the wiring 414 to which the input signal of the latch circuit 400 is given. The output of the NAND 412 is electrically connected to the wiring 415 to which the output signal of the latch circuit 400 is given. The other one of the inputs of NAND412 is electrically connected to the wiring to which the signal RSTB is given. A clock signal and an inverted signal of the clock signal are given to the analog switch 431. A clock signal and an inverted signal of the clock signal are given to the clocked inverter 413.

The logic circuit shown in FIG. 21 has a non-volatile latch circuit 400a and a non-volatile latch circuit 400b as the non-volatile latch circuit 400. The non-volatile latch circuit 400a is electrically connected to the wiring 414 to which the potential of the input signal is given from the circuit in the previous stage. The wiring 415 to which the potential of the output signal of the non-volatile latch circuit 400a is given is electrically connected to the wiring 414 to which the potential of the input signal of the non-volatile latch circuit 400b is given. The non-volatile latch circuit 400b is electrically connected to the wiring 415 that gives the potential of the output signal of the non-volatile latch circuit 400b to the subsequent circuit.

A clock signal φ1 and a clock signal inversion signal φ1b are given to the analog switch 431 of the non-volatile latch circuit 400a, and a clock signal φ2 and a clock signal inversion signal φ2b are given to the clocked inverter 413. Further, the analog switch 431 of the non-volatile latch circuit 400b is given a clock signal φ2 and a clock signal inversion signal φ2b, and the clocked inverter 413 is given a clock signal φ1 and a clock signal inversion signal φ1b.

By using a transistor using the oxide semiconductor according to the present embodiment as a semiconductor material constituting the channel formation region in a non-volatile latch circuit as a switching element of the data holding unit, the temperature operating range is wide and stable even at high temperatures. It is possible to realize a non-volatile latch circuit that operates and the stored logical state does not disappear even when the power is turned off, or a latch circuit that incorporates a data holding unit having a sufficiently long refresh period.

Further, since data is written by switching transistors, there is substantially no limit to the number of rewrites. Further, the write voltage is about the threshold voltage of the transistor, and it is possible to operate at a low voltage. Further, since the potential of the data holding unit is directly applied, the variation in the amount of charge held as data can be suppressed to be small, and the data can be easily read out.

By using the non-volatile latch circuit, various logic circuits can be realized. For example, power consumption can be reduced by turning off the power of unused blocks. In addition, since the logical state is memorized even when the power is turned off, it is possible to start the system when the power is turned on and shut down the system when the power is turned off at high speed and with low power consumption. Is.

This embodiment can be freely combined with other embodiments.

(Embodiment 7) In the present embodiment, the configuration of a non-volatile latch circuit, which is one aspect of the disclosed invention, will be described with reference to FIG. FIG. 22 shows an example different from that of FIG. FIG. 22 shows the configuration of the non-volatile latch circuit 400 having the latch portion 411 and the data holding portion 401 for holding the data of the latch portion.

In the non-volatile latch circuit 400 shown in FIG. 22, the output of the first element (D1) 412 is electrically connected to the input of the second element (D2) 413, and the output of the second element (D2) 413 is connected. Has a latch portion 411 having a loop structure electrically connected to the input of the first element (D1) 412, and a data holding portion 401 for holding the data of the latch portion.

The input of the first element (D1) 412 is electrically connected to the wiring 414 to which the input signal of the latch circuit is given. The output of the first element (D1) 412 is electrically connected to the wiring 415 to which the output signal of the latch circuit is given.

When there are multiple inputs of the first element (D1) 412, one of them can be electrically connected to the wiring 414 to which the input signal of the latch circuit is given. If there are multiple inputs for the second element (D2) 413, one of them can be electrically connected to the output of the first element (D1) 412.

As the first element (D1) 412, an element in which the input signal is inverted and the output is used can be used. For example, an inverter, NAND, NOR, clocked inverter, or the like can be used for the first element (D1) 412. Further, as the second element (D2) 413, an element in which the input signal is inverted and the output is used can be used. For example, an inverter, NAND, NOR, clocked inverter, or the like can be used for the second element (D2) 413.

The data holding unit 401 uses transistors 402a and transistors 402b, which use oxide semiconductors as semiconductor materials constituting the channel formation region, as switching elements. Further, it has a capacitance 404a electrically connected to the source electrode or drain electrode of the transistor 402a and a capacitance 404b electrically connected to the source electrode or drain electrode of the transistor 402b.

One of the electrodes having a capacitance of 404a is electrically connected to one of the source electrode and the drain electrode of the transistor 402a, and one of the electrodes having a capacitance of 404b is electrically connected to one of the source electrode and the drain electrode of the transistor 402b. .. The other of the source electrode and the drain electrode of the transistor 402a is electrically connected to the wiring 414 to which the input of the first element (D1) 412 and the input signal of the latch circuit are given. The other of the source electrode and the drain electrode of the transistor 402b is electrically connected to the wiring 415 to which the output of the first element (D1) 412 and the output signal of the latch circuit are given. The potential Vc is given to the other of the electrodes having a capacitance of 404a and the other of the electrodes having a capacitance of 404b.

The transistors 402a and 402b using this oxide semiconductor have a function of writing the data held in the latch portion 411 to the capacitance 404a and the capacitance 404b of the data holding portion 401. Further, the transistor 402a and the transistor 402b have a function of holding the data written in the capacity 404a and the capacity 404b of the data holding unit 401. Further, the transistor 402a and the transistor 402b have a function of reading the data held in the capacitance 404a and the capacitance 404b of the data holding unit 401 to the latch unit 411.

The operations of writing and holding the data held in the latch unit 411 to the data holding unit 401, reading the data from the data holding unit 401 to the latch unit 411, and rewriting the data will be described. First, a potential for turning on the respective transistors is supplied to the gate electrodes of the transistors 402a and 402b, and the transistors 402a and 402b are turned on.

As a result, the data held in the latch portion, that is, the potential of the input of the first element (D1) 412 held in the latch portion is given to one electrode of the capacitance 404a and held in the latch portion. The potential of the output of the first element (D1) 412 is applied to one electrode of capacitance 404b. As a result, the electric charge corresponding to the input potential of the first element (D1) 412 is accumulated in one electrode of the capacitance 404a, and the electric charge of the first element (D1) 412 is accumulated in one electrode of the capacitance 404b. Charges are accumulated (writing) according to the output potential.

After that, the potentials of the gate electrodes of the transistors 402a and 402b were set as the potentials at which the respective transistors were turned off, and the transistors 402a and 402b were turned off, so that they were accumulated in one of the electrodes having a capacitance of 404a and a capacitance of 404b. The charge is retained (retained).

Further, by supplying a potential for turning on the respective transistors to the gate electrodes of the transistors 402a and 402b and turning on the transistors 402a and 402b, one electrode having a capacitance of 404a and the first element (D1) are turned on. ) The charge is distributed by the input of 412, and the charge is distributed by one electrode of the capacitance 404b and the output of the first element (D1) 412. As a result, the input and output of the first element (D1) 412 are given a potential corresponding to the electric charge accumulated in one electrode of the capacitance 404a and the capacitance 404b. As a result, data can be read (read). The data can be rewritten in the same manner as the above-mentioned data writing and holding.

By using a transistor using the oxide semiconductor according to the present embodiment as a semiconductor material constituting the channel formation region in a non-volatile latch circuit as a switching element of the data holding unit, the temperature operating range is wide and stable even at high temperatures. It is possible to realize a non-volatile latch circuit that operates and the stored logical state does not disappear even when the power is turned off, or a latch circuit that incorporates a data holding unit having a sufficiently long refresh period.

Further, since data is written by switching transistors, there is substantially no limit to the number of rewrites. Further, the write voltage is about the threshold voltage of the transistor, and it is possible to operate at a low voltage. Further, since the potential of the data holding unit is directly applied, the variation in the amount of charge held as data can be suppressed to be small, and the data can be easily read out.

By using the non-volatile latch circuit, various logic circuits can be realized. For example, power consumption can be reduced by turning off the power of unused blocks. In addition, since the logical state is memorized even when the power is turned off, it is possible to start the system when the power is turned on and shut down the system when the power is turned off at high speed and with low power consumption. Is.

This embodiment can be freely combined with other embodiments.

(Embodiment 8) In the present embodiment, the configuration and operation of a non-volatile latch circuit, which is one aspect of the disclosed invention, will be described with reference to FIGS. 23 and 24.

FIG. 23 shows the configuration of the non-volatile latch circuit 400 having the latch portion 411 and the data holding portion 401 for holding the data of the latch portion. FIG. 24 shows an example of a timing chart of the non-volatile latch circuit 400.

FIG. 23 is an example in which the configuration of the latch portion 411 of FIG. 22 is specifically shown. FIG. 23 shows an example in which the inverter 412 is used as the first element and the inverter 413 is used as the second element in the configuration of the latch portion 411 of FIG. The configuration of the transistor 402a and the transistor 402b can be the same as that of the first embodiment or the second embodiment.

The latch portion 411 has an inverter 412 and an inverter 413. It has a loop structure in which the output of the inverter 412 is electrically connected to the input of the inverter 413, and the output of the inverter 413 is electrically connected to the input of the inverter 412. Further, the latch portion 411 has a switch 431 and a switch 432, and the output of the inverter 413 is electrically connected to the input of the inverter 412 via the switch 432.

The input of the inverter 412 is electrically connected to the wiring 414 to which the input signal of the latch circuit is given via the switch 431. The output of the inverter 412 is electrically connected to the wiring 415 to which the output signal of the latch circuit is given. The node connected to the input of the inverter 412 will be called node P. The node P is electrically connected to the wiring 414 to which the input signal of the latch circuit is given. Node P is also a node that is electrically connected to the output of the inverter 413. The potential of the node P is the same as the potential of the input of the inverter 412.

The data holding unit 401 uses transistors 402a and transistors 402b, which use oxide semiconductors as semiconductor materials constituting the channel formation region, as switching elements. Further, it has a capacitance 404a electrically connected to the source electrode or drain electrode of the transistor 402a and a capacitance 404b electrically connected to the source electrode or drain electrode of the transistor 402b.

One of the electrodes having a capacitance of 404a is electrically connected to one of the source electrode and the drain electrode of the transistor 402a, and one of the electrodes having a capacitance of 404b is electrically connected to one of the source electrode and the drain electrode of the transistor 402b. .. The other of the source electrode and the drain electrode of the transistor 402a is electrically connected to the wiring 414 to which the input signal of the latch circuit is given and the input (node P) of the inverter 412 of the latch portion.

The other of the source electrode and the drain electrode of the transistor 402b is electrically connected to the output of the wiring 415 to which the output signal of the latch circuit is given and the inverter 412 of the latch portion. The potential Vc is given to the other of the electrodes having a capacitance of 404a and the other of the electrodes having a capacitance of 404b. The nodes in which the transistor 402a and the capacitance 404a and the transistor 402b and the capacitance 404b are electrically connected are referred to as a node S1 and a node S2, respectively.

The transistors 402a and 402b using this oxide semiconductor have a function of writing the data held in the latch portion 411 to the capacitance 404a and the capacitance 404b of the data holding portion 401. Further, the transistor 402a and the transistor 402b have a function of holding the data written in the capacity 404a and the capacity 404b of the data holding unit 401. Further, the transistor 402a and the transistor 402b have a function of reading the data held in the capacitance 404a and the capacitance 404b of the data holding unit 401 to the latch unit 411.

The potential of the input signal IN is given to the wiring 414 from the circuit in the previous stage. The potential of the wiring 415 is given to the subsequent circuit as an output signal OUT. The potential of the clock signal φ1 is given to the switch 431. When a high level potential is applied to the clock signal φ1, the switch 431 is turned on. The potential of the clock signal φ2 is given to the switch 432. When a high level potential is applied to the clock signal φ2, the switch 432 is turned on. Control signals φ at the gates of transistor 402a and transistor 402b, respectively_LSThe potential of is given.

Control signal φ_LSWhen a high level potential is applied to, each transistor is turned on. In the normal operation period, the clock signal φ2 has a signal obtained by inverting the clock signal φ1. Here, an example is shown in which the transistor and the switch are turned on when the control signal and the clock signal are at a high level.

A high-level power supply voltage VDD and a low-level power supply voltage VSS are given to the inverter 412 and the inverter 413 of the latch portion 411, respectively.

Next, in FIGS. 24 (A) and 24 (B), the input signal IN and the output signal OUT during the period in which the non-volatile latch circuit 400 is in the operating state (operating period) and in the stopped state (non-operating period). , Control signal φ_LS, An example of the timing chart of the potentials of the clock signal φ1 and the clock signal φ2 is shown. Further, the potentials of the nodes S1 and S2 of the data holding unit 401, the node P of the latch unit 411, the inverter 412 of the latch unit 411, and the power supply voltage VDD-L of the inverter 413 are also shown.

Node S1 shows the potential of one electrode of capacitance 404a. Node S2 shows the potential of one electrode of capacitance 404b. A predetermined potential Vc is given to the other electrodes having a capacitance of 404a and a capacitance of 404b, respectively. For example, a ground potential is given.

First, FIG. 24 (A) will be described. In FIG. 24 (A), the period a, the period b, the period d, and the period e are the periods during which the latch circuit 400 is in the operating state (operating period), and the period c is the period during which the latch circuit 400 is stopped (non-operating period). Is. The period a and the period e are normal operating periods of the latch circuit 400, and high-level or low-level potentials are alternately applied to the clock signal φ1 and the clock signal φ2. Period b is the preparatory period before the non-operation period. Period b is also called the start-up period. The period d is the preparation period from the non-operating period to the start of the normal operating period. The period d is also called the start-up period.

During the normal operating period (period a), when a high-level potential is applied to the clock signal φ1 and a low-level potential is applied to the clock signal φ2, the switch 432 is turned off, the inverter loop is disconnected, and the switch 431 is turned on to input. The signal potential is input to the inverter 412. The potential of the input signal is inverted by the inverter 412 and given to the subsequent circuit as an output signal OUT. When a high level potential is applied to the clock signal φ1, if the potential of the input signal is high level, an output signal having a low level potential is obtained. When a high level potential is applied to the clock signal φ1, if the potential of the input signal is low level, an output signal having a high level potential can be obtained.

When a low-level potential is applied to the clock signal φ1 and a high-level potential is applied to the clock signal φ2, the switch 431 is turned off, the switch 432 is turned on, an inverter loop is formed, and the potential of the output signal OUT is maintained (data). Is latched, that is, the logical state of the latch circuit is retained.).

Control signal φ during normal operation period_LSIs given a potential for turning off the transistor 402a and the transistor 402b, and is not given a potential for turning on the transistor 402a and the transistor 402b. Node S1 and node S2 have a potential corresponding to the electric charge previously held. Here, it is an indefinite value.

Next, in the preparation period (period b) before the non-operation period, the control signal φ_LSWhen a potential for turning on the transistor 402a and the transistor 402b is given to the transistor 402a, the transistor 402a and the transistor 402b are turned on. As a result, the potential of the input (node P) of the inverter 412 of the latch part is given to one electrode (node S1) of the capacitance 404a, and the potential of the output (or the wiring 415 to which the output signal is given) of the inverter 412 of the latch part is given. Is given to one electrode (node S2) of capacitance 404b.

As a result, the electric charge corresponding to the potential of the input (node P) of the inverter 412 of the latch portion is accumulated in the capacitance 404a, and the output (or output signal) of the inverter 412 of the latch portion is given to the capacitance 404b. ) Charges are accumulated (writing) according to the potential. For example, control signal φ_LSIf the potential of the input (node P) of the inverter 412 of the latch portion is high level at the timing when the potential for turning on the transistor 402a and the transistor 402b is given to, the potential of the node S1 becomes high level. If the potential of the output (or the wiring 415 to which the output signal is given) of the inverter 412 of the latch portion is low level, the potential of the node S2 becomes low level.

After that, the control signal φ_LSIs given a potential to turn off the transistors 402a and 402b, each transistor is turned off, and the nodes S1 and S2 are in a floating state. As a result, the electric charges accumulated in the nodes S1 and S2 are retained (retained) as they are.

In the period b, the clock signal φ2 and the clock signal φ1 may maintain the potential at the end of the period a. Alternatively, the clock signal φ2 may be fixed at a high level and the clock signal φ1 may be fixed at a low level, and the data at the end of the period a may be latched.

Next, during the non-operating period (period c), the power supply is stopped, and the power supply voltages VDD-L of the inverter 412 and the inverter 413 of the latch portion 411 decrease. The clock signal φ1, the clock signal φ2, the input signal IN, the output signal OUT, and the potential of the node P may have any value between VDD and VSS. During this time, the control signal φ_LSThe potential of is held at a low level so that the transistors 402a and 402b are turned off. For example, it is held at the ground potential. By turning off the transistors 402a and 402b during the non-operating period (period c), the electric charges accumulated in the nodes S1 and S2 are retained (retained).

Next, after the non-operating period, the preparation period (period d) until the normal operating period is entered is entered. FIG. 24 (A) shows the control signal φ._LSAn example is shown in which the potentials of the node P and the output signal OUT are at a low level at the timing when the potentials for turning on the transistors 402a and 402b are given to.

In the period d, the clock signal φ2 is fixed at the high level and the clock signal φ1 is fixed at the low level before the power is supplied to the inverter 412 and the inverter 413 of the latch portion 411. In this state, the control signal φ_LSWhen the potential for turning on the transistor 402a and the transistor 402b is given to, the respective transistors are turned on, and the potentials held by the nodes S1 and S2 are given to the latch portion 411, respectively.

Specifically, the electric charge is distributed between the node S1 and the input of the inverter 412 (node P), and the input of the inverter 412 (node P) is given a potential corresponding to the electric charge accumulated in the node S1. Here, the potential of the input (node P) of the inverter 412 rises, and the potential of the node S1 decreases slightly.

Further, the electric charge is distributed between the node S2 and the output of the inverter 412 (or the wiring 415 to which the output signal is given), and the electric charge accumulated in the node S2 is distributed to the output of the inverter 412 (or the wiring 415 to which the output signal is given). The electric charge corresponding to is given. Here, both the potential of the input (node P) of the inverter 412 and the potential of the node S2 remain at low levels.

When power is supplied to the inverter 412 and the inverter 413 in this state, the input (node P) of the inverter 412 in the latch part becomes high level due to the potential difference between the input and the output of the inverter 412 and the inverter 413, respectively. The output of (or the wiring 415 to which the output signal is given) is at a low level.

As a result, the data in the data holding unit is read out to the latch unit, and the logical state of the latch circuit can be returned to the logical state before entering the non-operating period. By creating a potential difference between the input and output of each of the inverters 412 and 413 before the power is supplied in this way, the latch circuit can be used as a differential amplifier. As a result, more stable reading becomes possible as compared with FIG. 19 (B).

Also, when power is supplied and an inverter loop is formed, high-level or low-level potentials are applied to the potentials of the node P and the output signal OUT and held (data is latched). Then, the potentials of the node P and the output signal OUT are given to the nodes S1 and S2, respectively. As a result, high-level or low-level potential is supplied to the nodes S1 and S2 again. As a result, the potentials of the nodes S1 and S2 can be returned to the state before the fluctuation (also called rewriting).

After that, the control signal φ_LSIs given a potential to turn off the transistors 402a and 402b, each transistor is turned off, and the nodes S1 and S2 are in a floating state. As a result, the electric charges accumulated in the nodes S1 and S2 are retained (retained) as they are. The electric charge accumulated in node S1 and node S2 is then the control signal φ._LSIt is rewritten at the timing when the potential for turning on the transistor 402a and the transistor 402b is given to. Therefore, next, the control signal φ_LSThe charges accumulated in the nodes S1 and S2 are retained as they are until the timing at which the transistors 402a and the transistors 402b are turned on.

As described above, the data read to the latch part includes the distribution of electric charge between the node S1 and the input of the inverter 412 (node P), and the output of the node S2 and the inverter 412 (or the wiring 415 to which the output signal is given). It is done by the distribution of charges. If the charge corresponding to the high level potential is stored in the node S1 and the charge corresponding to the low level potential is stored in the node S2, the input of the inverter 412 before the transistors 402a and 402b are turned on (node). Regardless of the potential of P) and the output (or the wiring 415 to which the output signal is given), the potential of the input (node P) of the inverter 412 after charge distribution is the output (or output signal) of the inverter 412 after charge distribution. Is higher than the potential of the given wiring 415).

Further, when the electric charge corresponding to the low level potential is accumulated in the node S1 and the electric charge corresponding to the high level potential is accumulated in the node S2, the input of the inverter 412 before the transistors 402a and 402b are turned on. Regardless of the potential of (node P) and the output (or the wiring 415 to which the output signal is given), the potential of the input (node P) of the inverter 412 after charge distribution is the output (or output) of the inverter 412 after charge distribution. The potential should be lower than the potential of the wiring 415) to which the output signal is given. Also, ensure that both the input (node P) and output (or wiring 415 to which the output signal is given) potential of the inverter 412 after charge distribution are not too low. For example, the voltage should not be lower than the threshold voltage of the transistors constituting the inverter.

In order to do so, it is preferable that the capacity of the node S1 is larger than the capacity of the node P. That is, it is preferable that the capacity value of the capacity 404a electrically connected to the node S1 is larger than the capacity value of the input capacity (gate capacity of the transistor of the inverter) of the inverter 412 electrically connected to the node P. It is also effective to set a period in which the potential Vc is a value between VDD and VSS in the period d. This makes it possible to perform the read operation more stably.

By doing so, it is possible to read data to the latch part not only when the node P is low level and the output signal OUT is high level, but also when the node P is high level and the output signal OUT is low level. It is possible. In addition, it is possible to read data to the latch part not only when the electric charge corresponding to the high level potential is accumulated in the node S1 but also when the electric charge corresponding to the low level potential is accumulated in the node S1. is there.

Next, high-level and low-level potentials are alternately applied to the clock signal φ1 and the clock signal φ2, resulting in a normal operating state (period e). At the start of the normal operating period (period e), the clock signal φ1 and the clock signal φ2 may start from the same potential (same state) as at the end of the previous normal operating period (period a). It may start from the potential (next state) reversed from the end of the period a.

Next, FIG. 24 (B) will be described. In FIG. 24 (B), the operations of the period a, the period b, and the period c are the same as those in FIG. 24 (A).

Next, after the non-operating period, the preparation period (period d) until the normal operating period is entered is entered. FIG. 24 (B) shows the control signal φ._LSAn example is shown in which the potentials of the node P and the output signal OUT are at a high level at the timing when the potentials at which the transistors 402a and the transistors 402b are turned on are given.

In the period d, the clock signal φ2 is fixed at the high level and the clock signal φ1 is fixed at the low level before the power is supplied to the inverter 412 and the inverter 413 of the latch portion 411. In this state, the control signal φ_LSWhen the potential for turning on the transistor 402a and the transistor 402b is given to, the respective transistors are turned on, and the potentials held by the nodes S1 and S2 are given to the latch portion 411, respectively.

Specifically, the electric charge is distributed between the node S1 and the input of the inverter 412 (node P), and the input of the inverter 412 (node P) is given a potential corresponding to the electric charge accumulated in the node S1. Here, both the potential of the input (node P) of the inverter 412 and the potential of the node S1 remain at high levels.

Further, the electric charge is distributed between the node S2 and the output of the inverter 412 (or the wiring 415 to which the output signal is given), and the electric charge accumulated in the node S2 is distributed to the output of the inverter 412 (or the wiring 415 to which the output signal is given). The electric charge corresponding to is given. Here, the potential of the output (output signal OUT) of the inverter 412 decreases, and the potential of the node S2 rises slightly.

When power is supplied to the inverter 412 and the inverter 413 in this state, the input (node P) of the inverter 412 in the latch part becomes high level due to the potential difference between the input and the output of the inverter 412 and the inverter 413, respectively. The output of (or the wiring 415 to which the output signal is given) is at a low level.

As a result, the data in the data holding unit is read out to the latch unit, and the logical state of the latch circuit can be returned to the logical state before entering the non-operating period. By creating a potential difference between the input and output of each of the inverters 412 and 413 before the power is supplied in this way, the latch circuit can be used as a differential amplifier. As a result, more stable reading becomes possible as compared with FIG. 19 (B).

Also, when power is supplied and an inverter loop is formed, high-level or low-level potentials are applied to the potentials of the node P and the output signal OUT and held (data is latched). Then, the potentials of the node P and the output signal OUT are given to the nodes S1 and S2, respectively. As a result, high-level or low-level potential is supplied to the nodes S1 and S2 again. As a result, the potentials of the nodes S1 and S2 can be returned to the state before the fluctuation (also called rewriting).

After that, the control signal φ_LSIs given a potential to turn off the transistors 402a and 402b, each transistor is turned off, and the nodes S1 and S2 are in a floating state. As a result, the electric charges accumulated in the nodes S1 and S2 are retained (retained) as they are. The electric charge accumulated in node S1 and node S2 is then the control signal φ._LSIt is rewritten at the timing when the potential for turning on the transistor 402a and the transistor 402b is given to. Therefore, next, the control signal φ_LSThe charges accumulated in the nodes S1 and S2 are retained as they are until the timing at which the transistors 402a and the transistors 402b are turned on.

Next, high-level and low-level potentials are alternately applied to the clock signal φ1 and the clock signal φ2, resulting in a normal operating state (period e). At the start of the normal operating period (period e), the clock signal φ1 and the clock signal φ2 may start from the same potential (same state) as at the end of the previous normal operating period (period a). It may start from the potential (next state) reversed from the end of the period a.

Although an example in which a potential difference is generated between the input and the output of each of the inverters 412 and 413 before the power is supplied is shown here, the configuration of the non-volatile latch circuit shown in the present embodiment ( In FIG. 23), it is also possible to operate using the same timing chart as in FIG. 19 (B).

It is also effective to set a period in which the potential Vc is a value between VDD and VSS in the period d. This makes it possible to perform the read operation more stably.

By using a non-volatile latch circuit that uses a transistor that uses an oxide semiconductor as the semiconductor material that constitutes the channel formation region according to this embodiment as a switching element of the data holding unit, the temperature operating range is wide and even at high temperatures. It is possible to realize a non-volatile latch circuit that operates stably and does not erase the stored logical state even when the power is turned off, or a latch circuit that incorporates a data holding unit having a sufficiently long refresh period.

Further, since data is written by switching transistors, there is substantially no limit to the number of rewrites. Further, the write voltage is about the threshold voltage of the transistor, and it is possible to operate at a low voltage. Further, since the potential of the data holding unit is directly applied, the variation in the amount of charge held as data can be suppressed to be small, and the data can be easily read out. Further, when the latch circuit is used as a differential amplifier, stable reading becomes possible.

By using the non-volatile latch circuit, various logic circuits can be realized. For example, power consumption can be reduced by turning off the power of unused blocks. In addition, since the logical state is memorized even when the power is turned off, it is possible to start the system when the power is turned on and shut down the system when the power is turned off at high speed and with low power consumption. Is.

This embodiment can be freely combined with other embodiments.

(Embodiment 9) In the present embodiment, the operation of a non-volatile latch circuit, which is one aspect of the disclosed invention, will be described with reference to FIG. The configuration of the non-volatile latch circuit is the same as in FIG. 23, and the timing chart shows an example different from those in FIGS. 24 (A) and 24 (B).

FIG. 25 shows the input signal IN, the output signal OUT, and the control signal φ during the period (operating period) and the stopped state (non-operating period) of the non-volatile latch circuit 400._LS, An example of the timing chart of the potentials of the clock signal φ1 and the clock signal φ2 is shown. Further, the potentials of the nodes S1 and S2 of the data holding unit 401, the node P of the latch unit 411, the inverter 412 of the latch unit 411, the power supply voltage VDD-L of the inverter 413, the capacity 404a, and the potential Vc of the other electrode of the capacity 404b Is also shown. Node S1 shows the potential of one electrode of capacitance 404a. Node S2 shows the potential of one electrode of capacitance 404b.

In FIG. 25, the period a, the period b, the period d, and the period e are the periods in which the latch circuit 400 is in the operating state (operating period), and the period c is the period in which the latch circuit 400 is in the stopped state (non-operating period). The period a and the period e are normal operating periods of the latch circuit 400, and high-level or low-level potentials are alternately applied to the clock signal φ1 and the clock signal φ2. Period b is the preparatory period before the non-operation period. Period b is also called the start-up period. The period d is the preparation period from the non-operating period to the start of the normal operating period. The period d is also called the start-up period.

In FIG. 25, the operations of the period a and the period b are the same as those in FIG. 24. Next, during the non-operating period (period c), the power supply is stopped, and the power supply voltages VDD-L of the inverter 412 and the inverter 413 of the latch portion 411 decrease. The clock signal φ1, the clock signal φ2, and the input signal IN may take any value between VDD and VSS. During this time, the control signal φ_LSThe potential of is held at a low level so that the transistors 402a and 402b are turned off. For example, it is held at the ground potential.

By turning off the transistors 402a and 402b during the non-operating period (period c), the electric charges accumulated in the nodes S1 and S2 are retained (retained). Further, the output signal OUT is held at a low level. In addition, the potential of node P gradually decreases.

Next, after the non-operating period, the preparation period (period d) until the normal operating period is entered is entered. In the period d, the clock signal φ2 is fixed at the high level and the clock signal φ1 is fixed at the low level before the power is supplied to the inverter 412 and the inverter 413 of the latch portion 411. In this state, the control signal φ_LSWhen the potential for turning on the transistor 402a and the transistor 402b is given to, the respective transistors are turned on, and the potentials held by the nodes S1 and S2 are given to the latch portion 411, respectively.

Specifically, the electric charge is distributed between the node S1 and the input (node P) of the inverter 412. And the control signal φ_LSAt the timing when the potential for turning on the transistor 402a is given to, a predetermined potential is given to the potential Vc of the other electrode having the capacitance 404a. The potential Vc is raised from the low level potential to a potential between low and high levels. As a result, the input (node P) of the inverter 412 is given a potential determined by the distribution of electric charge with the node S1 plus an increment of the potential Vc of the other electrode having the capacitance 404a. Here, the potential of the input (node P) of the inverter 412 rises, and the potential of the node S1 decreases slightly.

Further, the electric charge is distributed between the node S2 and the output of the inverter 412 (or the wiring 415 to which the output signal is given). And the control signal φ_LSAt the timing when the potential for turning on the transistor 402b is given to, a predetermined potential is given to the potential Vc of the other electrode having the capacitance 404b. The potential Vc is raised from the low level potential to a potential between low and high levels.

As a result, the output of the inverter 412 (or the wiring 415 to which the output signal is given) is given a potential determined by the distribution of electric charge with the node S2, plus an increment of the potential Vc of the other electrode having a capacitance of 404b. .. Here, the potential of the output of the inverter 412 (or the wiring 415 to which the output signal is given) and the node S2 rise slightly due to the increase in the potential Vc of the other electrode having the capacitance 404b.

When power is supplied to the inverter 412 and the inverter 413 in this state, the input (node P) of the inverter 412 in the latch part becomes high level due to the potential difference between the input and the output of the inverter 412 and the inverter 413, respectively. The output of (or the wiring 415 to which the output signal is given) is at a low level.

As a result, the data in the data holding unit is read out to the latch unit, and the logical state of the latch circuit can be returned to the logical state before entering the non-operating period. By creating a potential difference between the input and output of each of the inverters 412 and 413 before the power is supplied in this way, the latch circuit can be used as a differential amplifier. As a result, more stable reading becomes possible as compared with FIG. 19 (B).

Also, when power is supplied and an inverter loop is formed, high-level or low-level potentials are applied to the potentials of the node P and the output signal OUT and held (data is latched). Then, the potentials of the node P and the output signal OUT are given to the nodes S1 and S2, respectively. As a result, high-level or low-level potential is supplied to the nodes S1 and S2 again. As a result, the potentials of the nodes S1 and S2 can be returned to the state before the fluctuation (also called rewriting).

Then, the potential Vc of the other electrode of the capacitance is returned to a low level potential.

After that, the control signal φ_LSIs given a potential to turn off the transistors 402a and 402b, each transistor is turned off, and the nodes S1 and S2 are in a floating state. As a result, the electric charges accumulated in the nodes S1 and S2 are retained (retained) as they are.

The electric charge accumulated in node S1 and node S2 is then the control signal φ._LSIt is rewritten at the timing when the potential for turning on the transistor 402a and the transistor 402b is given to. Therefore, next, the control signal φ_LSThe charges accumulated in the nodes S1 and S2 are retained as they are until the timing at which the transistors 402a and the transistors 402b are turned on.

As described above, the data read to the latch part includes the distribution of electric charge between the node S1 and the input of the inverter 412 (node P), and the output of the node S2 and the inverter 412 (or the wiring 415 to which the output signal is given). It is done by the distribution of charges. If the charge corresponding to the high level potential is stored in the node S1 and the charge corresponding to the low level potential is stored in the node S2, the input of the inverter 412 before the transistors 402a and 402b are turned on (node). Regardless of the potential of P) and the output (or the wiring 415 to which the output signal is given), the potential of the input (node P) of the inverter 412 after charge distribution is the output (or output signal) of the inverter 412 after charge distribution. Is higher than the potential of the given wiring 415).

Further, when the electric charge corresponding to the low level potential is accumulated in the node S1 and the electric charge corresponding to the high level potential is accumulated in the node S2, the input of the inverter 412 before the transistors 402a and 402b are turned on. Regardless of the potential of (node P) and the output (or the wiring 415 to which the output signal is given), the potential of the input (node P) of the inverter 412 after charge distribution is the output (or output) of the inverter 412 after charge distribution. The potential should be lower than the potential of the wiring 415) to which the output signal is given. Also, ensure that both the input (node P) and output (or wiring 415 to which the output signal is given) potential of the inverter 412 after charge distribution are not too low. For example, the voltage should not be lower than the threshold voltage of the transistors constituting the inverter.

In order to do so, it is preferable that the capacity of the node S1 is larger than the capacity of the node P. That is, it is preferable that the capacity value of the capacity 404a electrically connected to the node S1 is larger than the capacity value of the input capacity (gate capacity of the transistor of the inverter) of the inverter 412 electrically connected to the node P. It is also effective to set a period in which the potential Vc is a value between VDD and VSS in the period d. This makes it possible to perform the read operation more stably.

By doing so, it is possible to read data to the latch part not only when the node P is low level and the output signal OUT is high level, but also when the node P is high level and the output signal OUT is low level. It is possible. In addition, it is possible to read data to the latch part not only when the electric charge corresponding to the high level potential is accumulated in the node S1 but also when the electric charge corresponding to the low level potential is accumulated in the node S1. is there.

In particular, as described in this embodiment, the control signal φ_LSBy applying a predetermined potential to the potential Vc of the other electrode of the capacitance at the timing when the potential at which the transistors 402a and 402b are turned on is given to the transistor, the reading can be performed more stably.

For example, when the capacitance values of the capacitances 404a and 404b are small, or when the power supply is stopped for a long period of time, the input (node P) and output (or wiring 415 to which the output signal is given) of the inverter 412 after the charge is distributed). It may be difficult to maintain the potential difference between the two, or the potential of the input (node P) and output (or wiring 415 to which the output signal is given) of the inverter 412 after charge distribution may become low, and the read stability may decrease. There is.

Even in such a case, by applying a predetermined potential to the potential Vc of the other electrode having the capacitance 404a and the capacitance 404b, the input (node P) and output (or output signal) of the inverter 412 after charge distribution can be obtained. The potential of the given wiring 415) can be controlled to an appropriate potential. As a result, stable reading can be performed. That is, it is possible to operate even with a capacity having a smaller capacity value, and it is possible to reduce the size. Alternatively, the data retention period can be extended.

Next, high-level and low-level potentials are alternately applied to the clock signal φ1 and the clock signal φ2, resulting in a normal operating state (period e). At the start of the normal operating period (period e), the clock signal φ1 and the clock signal φ2 may start from the same potential (same state) as at the end of the previous normal operating period (period a). It may start from the potential (next state) reversed from the end of the period a.

Although an example in which a potential difference is generated between the input and the output of each of the inverters 412 and 413 before the power is supplied is shown here, the configuration of the non-volatile latch circuit shown in the present embodiment ( In FIG. 23), it is also possible to operate using the same timing chart as in FIG. 19 (B).

By using a non-volatile latch circuit that uses a transistor that uses an oxide semiconductor as the semiconductor material that constitutes the channel formation region according to this embodiment as a switching element of the data holding unit, the temperature operating range is wide and even at high temperatures. It is possible to realize a non-volatile latch circuit that operates stably and does not erase the stored logical state even when the power is turned off, or a latch circuit that incorporates a data holding unit having a sufficiently long refresh period.

Further, since data is written by switching transistors, there is substantially no limit to the number of rewrites. Further, the write voltage is about the threshold voltage of the transistor, and it is possible to operate at a low voltage. Further, since the potential of the data holding unit is directly applied, the variation in the amount of charge held as data can be suppressed to be small, and the data can be easily read out. In addition, the capacity of the data holding unit can be made smaller, and the size can be reduced.

By using the non-volatile latch circuit, various logic circuits can be realized. For example, power consumption can be reduced by turning off the power of unused blocks. In addition, since the logical state is memorized even when the power is turned off, it is possible to start the system when the power is turned on and shut down the system when the power is turned off at high speed and with low power consumption. Is.

This embodiment can be freely combined with other embodiments.

(Embodiment 10) The present embodiment describes a configuration of a logic circuit having a plurality of non-volatile latch circuits, which is one aspect of the disclosed invention, with reference to FIG. 26.

FIG. 26 shows the configuration of a logic circuit having two non-volatile latch circuits 400 having a latch portion 411 and a data holding portion 401 for holding data in the latch portion. This logic circuit is called D-FF, and is used as a register in, for example, a CPU or various logic circuits.

The configuration of the data holding unit 401 is the same as that shown in FIG. The configuration of the latch portion 411 is an example in which the NAND is used as the first element and the clocked inverter is used as the second element in the configuration of the latch portion 411 of FIG.

The latch portion 411 has a NAND 412 and a clocked inverter 413. It has a loop structure in which the output of the NAND 412 is electrically connected to the input of the clocked inverter 413 and the output of the clocked inverter 413 is electrically connected to the input of the NAND 412. Further, the latch portion 411 has an analog switch 431.

One of the inputs of the NAND 412 is electrically connected via the analog switch 431 to the wiring 414 to which the input signal of the latch circuit 400 is given. The output of the NAND 412 is electrically connected to the wiring 415 to which the output signal of the latch circuit 400 is given. The other one of the inputs of the NAND412 is electrically connected to the wiring to which the signal RSTB is given. A clock signal and an inverted signal of the clock signal are given to the analog switch 431. A clock signal and an inverted signal of the clock signal are given to the clocked inverter 413.

The logic circuit shown in FIG. 26 has a non-volatile latch circuit 400a and a non-volatile latch circuit 400b as the non-volatile latch circuit 400. The non-volatile latch circuit 400a is electrically connected to the wiring 414 to which the potential of the input signal is given from the circuit in the previous stage. The wiring 415 to which the potential of the output signal of the non-volatile latch circuit 400a is given is electrically connected to the wiring 414 to which the potential of the input signal of the non-volatile latch circuit 400b is given. The non-volatile latch circuit 400b is electrically connected to the wiring 415 that gives the potential of the output signal of the non-volatile latch circuit 400b to the subsequent circuit.

A clock signal φ1 and a clock signal inversion signal φ1b are given to the analog switch 431 of the non-volatile latch circuit 400a, and a clock signal φ2 and a clock signal inversion signal φ2b are given to the clocked inverter 413. Further, the analog switch 431 of the non-volatile latch circuit 400b is given a clock signal φ2 and a clock signal inversion signal φ2b, and the clocked inverter 413 is given a clock signal φ1 and a clock signal inversion signal φ1b.

By using a non-volatile latch circuit that uses a transistor that uses an oxide semiconductor as the semiconductor material that constitutes the channel formation region according to this embodiment as a switching element of the data holding unit, the temperature operating range is wide and even at high temperatures. It is possible to realize a non-volatile latch circuit that operates stably and does not erase the stored logical state even when the power is turned off, or a latch circuit that incorporates a data holding unit having a sufficiently long refresh period.

Further, since data is written by switching transistors, there is substantially no limit to the number of rewrites. Further, the write voltage is about the threshold voltage of the transistor, and it is possible to operate at a low voltage. Further, since the potential of the data holding unit is directly applied, the variation in the amount of charge held as data can be suppressed to be small, and the data can be easily read out.

By using the non-volatile latch circuit, various logic circuits can be realized. For example, power consumption can be reduced by turning off the power of unused blocks. In addition, since the logical state is memorized even when the power is turned off, it is possible to start the system when the power is turned on and shut down the system when the power is turned off at high speed and with low power consumption. Is.

This embodiment can be freely combined with other embodiments.

(Embodiment 11) Next, regarding another example of a method for manufacturing a transistor using an oxide semiconductor, which can be used as the transistor 402 in the previous embodiment (Embodiment 1, Embodiment 2, etc.). , This will be described with reference to FIG. 27. In the present embodiment, a case where a highly purified oxide semiconductor (particularly an amorphous structure) is used will be described in detail. In the following, a top gate type transistor will be described as an example, but the transistor configuration does not have to be limited to the top gate type.

First, the insulating layer 202 is formed on the lower substrate 200. Then, the oxide semiconductor layer 206 is formed on the insulating layer 202 (see FIG. 27 (A)).

Here, the lower layer substrate 200 corresponds to the substrate on which the lower transistor 160 and the like are formed in the previous embodiment. For the details, the above embodiment can be taken into consideration. The surface of the lower substrate 200 is preferably as flat as possible, and therefore, the height difference of the surface is adjusted to 5 nm or less, preferably 1 nm or less, or the surface by a chemical mechanical polishing method (CMP method) or the like. The root mean square (RMS) of the roughness should be 2 nm or less, preferably 0.4 nm or less.

The insulating layer 202 functions as a base, and can be formed in the same manner as the insulating layer 168 and the protective insulating layer 144 in the previous embodiment. For details, the above embodiment may be taken into consideration. It is desirable that the insulating layer 202 is formed so as not to contain hydrogen or water as much as possible.

The oxide semiconductor layer 206 includes a quaternary metal oxide, In-Sn-Ga-Zn-O, a ternary metal oxide, In-Ga-Zn-O, and In-Sn-Zn-. O-based, In-Al-Zn-O-based, Sn-Ga-Zn-O-based, Al-Ga-Zn-O-based, Sn-Al-Zn-O-based, and In-, which is a binary metal oxide. Zn-O series, Sn-Zn-O series, Al-Zn-O series, Zn-Mg-O series, Sn-Mg-O series, In-Mg-O series, and In-, which is a unified metal oxide. It can be formed by using oxide semiconductors such as O-based, Sn-O-based, and Zn-O-based.

Among them, the In-Ga-Zn-O-based oxide semiconductor material has a sufficiently high resistance when there is no electric field, can sufficiently reduce the off-current, and has a high field effect mobility, so that it is a semiconductor. It is suitable as a semiconductor material used in an apparatus.

InGaO is a typical example of an In-Ga-Zn-O-based oxide semiconductor material.₃(ZnO)_mSome are represented by (m&gt; 0). Also, use M instead of Ga and InMO₃(ZnO)_mThere are oxide semiconductor materials described as (m&gt; 0). Here, M is one metal element or a plurality of metal elements selected from gallium (Ga), aluminum (Al), iron (Fe), nickel (Ni), manganese (Mn), cobalt (Co), and the like. Shown. For example, as M, Ga, Ga and Al, Ga and Fe, Ga and Ni, Ga and Mn, Ga and Co and the like can be applied. It should be noted that the above composition is derived from the crystal structure and is merely an example.

In the present embodiment, the oxide semiconductor layer 206 having an amorphous structure is formed by a sputtering method using an In-Ga-Zn-O-based metal oxide target.

Examples of the metal oxide target for producing the oxide semiconductor layer 206 by the sputtering method include In.₂O₃: Ga₂O₃A metal oxide target having a composition ratio of: ZnO = 1: 1: 1 [mol ratio]) may be used. Also, In₂O₃: Ga₂O₃: ZnO = 1: 1: 2 [mol ratio] of metal oxide targets and In₂O₃: Ga₂O₃A metal oxide target having a composition ratio of: ZnO = 1: 1: 4 [mol ratio] can also be used.

The relative density of the oxide semiconductor in the metal oxide target is 80% or more, preferably 95% or more, and more preferably 99.9% or more. By using a metal oxide target having a high relative density, it is possible to form an oxide semiconductor layer 206 having a dense structure.

The formation atmosphere of the oxide semiconductor layer 206 is preferably a rare gas (typically argon) atmosphere, an oxygen atmosphere, or a mixed atmosphere of a rare gas (typically argon) and oxygen. Specifically, for example, it is preferable to use a high-purity gas atmosphere in which impurities such as hydrogen, water, hydroxyl groups, and hydrides are removed to a concentration of about several ppm (preferably about several ppb).

When forming the oxide semiconductor layer 206, for example, the substrate is held in a processing chamber kept under reduced pressure, and the temperature of the substrate is 100 ° C or higher and 550 ° C or lower, preferably 200 ° C or higher and 400 ° C. Heat the substrate as follows. Then, while removing the water in the treatment chamber, a sputter gas from which hydrogen, water, etc. have been removed is introduced, and the oxide semiconductor layer 206 is formed using the target. By forming the oxide semiconductor layer 206 while heating the substrate, the concentration of impurities contained in the oxide semiconductor layer 206 can be reduced. In addition, damage due to sputtering can be reduced. In order to remove the water in the treatment chamber, it is preferable to use an adsorption type vacuum pump. For example, a cryopump, an ion pump, a titanium sublimation pump, or the like can be used. Further, a turbo pump to which a cold trap is added may be used. By exhausting with a cryopump, hydrogen, water, and the like are removed from the treatment chamber, so that the concentration of impurities in the oxide semiconductor layer 206 can be reduced.

The conditions for forming the oxide semiconductor layer 206 are, for example, a distance of 170 mm between the substrate and the target, a pressure of 0.4 Pa, a direct current (DC) power of 0.5 kW, and an atmosphere of oxygen (oxygen flow ratio 100%). Alternatively, conditions such as an argon (argon flow ratio 100%) atmosphere or a mixed atmosphere of oxygen and argon can be applied. It is preferable to use a pulsed direct current (DC) power source because dust (powder-like substance formed at the time of film formation) can be reduced and the film thickness distribution is also reduced. The thickness of the oxide semiconductor layer 206 is 2 nm or more and 200 nm or less, preferably 5 nm or more and 30 nm or less. However, since the appropriate thickness differs depending on the oxide semiconductor material to be applied, the application of the semiconductor device, etc., the thickness may be selected according to the material to be used, the application, and the like.

Before forming the oxide semiconductor layer 206 by the sputtering method, it is preferable to introduce argon gas and perform reverse sputtering to generate plasma to remove deposits on the surface of the insulating layer 202. Here, the reverse sputtering refers to a method in which ions collide with a sputtering target in normal sputtering, and conversely, the surface is modified by colliding ions with the treated surface. As a method of colliding ions with the treated surface, there is a method of applying a high frequency voltage to the treated surface side in an argon atmosphere to generate plasma in the vicinity of the substrate. An atmosphere of nitrogen, helium, oxygen or the like may be applied instead of the argon atmosphere.

Next, the oxide semiconductor layer 206 is processed by a method such as etching using a mask to form an island-shaped oxide semiconductor layer 206a.

Either dry etching or wet etching may be used for etching the oxide semiconductor layer 206. Of course, both can be used in combination. Etching conditions (etching gas, etching solution, etching time, temperature, etc.) are appropriately set according to the material so that the oxide semiconductor layer can be etched into a desired shape. For details, the previous embodiment can be taken into consideration. The etching of the oxide semiconductor layer 206 can be performed in the same manner as the etching of the oxide semiconductor layer in the previous embodiment. For details, the above embodiment may be taken into consideration.

After that, it is desirable to perform a heat treatment (first heat treatment) on the oxide semiconductor layer 206a. By this first heat treatment, excess hydrogen (including water and hydroxyl groups) in the oxide semiconductor layer 206a is removed, the structure of the oxide semiconductor layer 206a is adjusted, and defects in the oxide semiconductor layer 206a are reduced. Can be done. The temperature of the first heat treatment is, for example, 300 ° C or more and 550 ° C or less, or 400 ° C or more and 550 ° C or less.

The heat treatment can be performed, for example, by introducing the lower layer substrate 200 into an electric furnace using a resistance heating element or the like, and performing the heat treatment under a nitrogen atmosphere at 450 ° C. for 1 hour. During this period, the oxide semiconductor layer 206a is kept out of contact with the atmosphere so that water and hydrogen are not mixed.

The heat treatment apparatus is not limited to an electric furnace, and an apparatus for heating an object to be processed by heat conduction from a medium such as a heated gas or heat radiation may be used. For example, an RTA (Rapid Thermal Anneal) device such as a GRTA (Gas Rapid Thermal Anneal) device or an LRTA (Lamp Rapid Thermal Anneal) device can be used. The LRTA device is a device that heats an object to be processed by radiating light (electromagnetic waves) emitted from lamps such as halogen lamps, metal halide lamps, xenon arc lamps, carbon arc lamps, high-pressure sodium lamps, and high-pressure mercury lamps. The GRTA device is a device that performs heat treatment using a high-temperature gas. As the gas, a rare gas such as argon or an inert gas such as nitrogen that does not react with the object to be treated by heat treatment is used.

For example, as the first heat treatment, a GRTA treatment may be performed in which the substrate is put into an inert gas atmosphere, heated for several minutes, and then the substrate is taken out from the inert gas atmosphere. The GRTA treatment enables high temperature heat treatment in a short time. Further, since the heat treatment is performed for a short time, it can be applied even under temperature conditions exceeding the heat resistant temperature of the substrate.

During the treatment, the atmosphere of the inert gas may be switched to an atmosphere containing oxygen. This is because defects caused by oxygen deficiency can be reduced by performing the first heat treatment in an atmosphere containing oxygen.

For example, when an electric furnace is used for the first heat treatment, the atmosphere can be switched when the temperature of the heat treatment is lowered. For example, the atmosphere during heat treatment (constant temperature) can be an inert gas atmosphere such as nitrogen or a rare gas (helium, neon, argon, etc.), and can be switched to an atmosphere containing oxygen when the temperature is lowered. As the atmosphere containing oxygen, oxygen gas or a gas obtained by mixing oxygen gas and nitrogen gas can be used.

As the inert gas atmosphere, it is desirable to apply an atmosphere containing nitrogen or a rare gas (helium, neon, argon, etc.) as a main component and not containing water, hydrogen, or the like. For example, the purity of nitrogen and rare gases such as helium, neon, and argon to be introduced into the heat treatment equipment is 6N (99.9999%) or more, preferably 7N (99.99999%) or more (that is, the impurity concentration is 1ppm or less, preferably 0.1. ppm or less).

In any case, by reducing impurities by the first heat treatment and forming an i-shaped or substantially i-shaped oxide semiconductor layer 206a, a transistor having extremely excellent characteristics can be realized. ..

The first heat treatment can also be performed on the oxide semiconductor layer 206 before being processed into the island-shaped oxide semiconductor layer 206a. In that case, after the first heat treatment, the lower layer substrate 200 is taken out from the heating device and a photolithography step is performed.

Since the first heat treatment has the effect of removing hydrogen and water, the first heat treatment can also be called a dehydration treatment, a dehydrogenation treatment, or the like. The dehydration treatment and the dehydrogenation treatment can also be performed at a timing such as after the formation of the oxide semiconductor layer, after laminating the source electrode or the drain electrode on the oxide semiconductor layer 206a, and the like. Further, such dehydration treatment and dehydrogenation treatment may be performed not only once but also a plurality of times.

Next, the conductive layer is formed so as to be in contact with the oxide semiconductor layer 206a. Then, the conductive layer is selectively etched to form the source electrode or drain electrode 208a and the source electrode or drain electrode 208b (see FIG. 27 (B)). The step is the same as the step relating to the source electrode or the drain electrode 142a of the previous embodiment. For details, the previous embodiment can be taken into consideration.

Next, the gate insulating layer 212 in contact with a part of the oxide semiconductor layer 206a is formed. (See Figure 27 (C)). For details, the description regarding the gate insulating layer of the previous embodiment can be referred to.

After the formation of the gate insulating layer 212, it is desirable to perform the second heat treatment in an inert gas atmosphere or an oxygen atmosphere. The heat treatment temperature is 200 ° C or higher and 450 ° C or lower, preferably 250 ° C or higher and 350 ° C or lower. For example, heat treatment may be performed at 250 ° C. for 1 hour in a nitrogen atmosphere. By performing the second heat treatment, it is possible to reduce variations in the electrical characteristics of the transistor. When the gate insulating layer 212 contains oxygen, oxygen is supplied to the oxide semiconductor layer 206a to reduce the oxygen deficiency of the oxide semiconductor layer 206a, and the oxide semiconductor layer 206a is as close to i-type (intrinsic semiconductor) or i-type as possible. It is also possible to form an oxide semiconductor layer.

In the present embodiment, the second heat treatment is performed immediately after the formation of the gate insulating layer 212, but the timing of the second heat treatment is not particularly limited to this.

Next, the gate electrode 214 is formed in the region on the gate insulating layer 212 that overlaps with the oxide semiconductor layer 206a (see FIG. 27 (D)). The gate electrode 214 can be formed by forming a conductive layer on the gate insulating layer 212 and then selectively patterning the conductive layer. For details, the description regarding the gate electrode of the previous embodiment can be referred to.

Next, the interlayer insulating layer 216 and the interlayer insulating layer 218 are formed on the gate insulating layer 212 and the gate electrode 214 (see FIG. 27 (E)). The interlayer insulating layer 216 and the interlayer insulating layer 218 can be formed by using a PVD method, a CVD method, or the like. Further, it can be formed by using a material containing an inorganic insulating material such as silicon oxide, silicon oxynitride, silicon nitride, hafnium oxide, aluminum oxide, and tantalum pentoxide. In the present embodiment, the interlayer insulating layer 216 and the interlayer insulating layer 218 are laminated, but one aspect of the disclosed invention is not limited to this. It may be one layer or a laminated structure of three or more layers.

It is desirable that the interlayer insulating layer 218 is formed so that its surface is flat. This is because by forming the interlayer insulating layer 218 so that the surface becomes flat, electrodes, wiring, and the like can be suitably formed on the interlayer insulating layer 218.

From the above, the transistor 250 using the highly purified oxide semiconductor layer 206a is completed.

The transistor 250 shown in FIG. 27 (E) has an oxide semiconductor layer 206a provided on the lower substrate 200 via an insulating layer 202, and a source electrode or drain electrode 208a electrically connected to the oxide semiconductor layer 206a. The source electrode or drain electrode 208b, the oxide semiconductor layer 206a, the source electrode or drain electrode 208a, the gate insulating layer 212 covering the source electrode or drain electrode 208b, the gate electrode 214 on the gate insulating layer 212, and the gate insulating layer 212. It also has an interlayer insulating layer 216 on the gate electrode 214 and an interlayer insulating layer 218 on the interlayer insulating layer 216.

In the transistor 250 shown in the present embodiment, the oxide semiconductor layer 206a is highly purified, so that the hydrogen concentration is 5 × 10.¹⁹/cm³Below, preferably 5x10¹⁸/cm³Below, more preferably 5x10¹⁷/cm³Below, more preferably 1x10¹⁶/cm³Will be less than. The carrier density of the oxide semiconductor layer 206a is the carrier density (1 × 10) in a general silicon wafer.¹⁴/cm³A sufficiently low value (eg 1x10) compared to the degree)¹²/cm³Less than, preferably 1x10¹¹/cm³Less than). As a result, the off-current becomes sufficiently small. For example, drain voltage V_DIs + 1V or + 10V and the gate voltage V_GIn the range of -5V to -20V, the off-current at room temperature is 1x10.^-13A or less. Further, the above-mentioned transistor has a normally-off transistor characteristic. Therefore, the off-current, that is, the leakage current when the voltage between the gate and the source electrode is almost 0 is significantly smaller than that of the transistor using silicon. For example, the unit channel width leakage current at room temperature is 10 aA / μm or less.

By using the oxide semiconductor layer 206a that has been purified and purified in this way, the off-current of the transistor can be sufficiently reduced.

In the present embodiment, the case where the transistor 250 is used as the transistor 402 shown in the previous embodiment has been described, but it is not necessary to interpret the disclosed invention in a limited manner. For example, by sufficiently enhancing the electrical characteristics of the oxide semiconductor, it is possible to use the oxide semiconductor for all the transistors including the transistors constituting the integrated circuit. In such a case, it is not necessary to have a laminated structure as shown in the previous embodiment. In this case, for example, it is possible to form a semiconductor device using a substrate such as a glass substrate.

As described above, the configurations and methods shown in the present embodiment can be appropriately combined with the configurations and methods shown in other embodiments.

(Embodiment 12) Next, another example of a method for manufacturing a transistor using an oxide semiconductor, which can be used as the transistor 402 in the previous embodiment (Embodiment 1, Embodiment 2, etc.). Will be described with reference to FIG. 28. In the present embodiment, when a first oxide semiconductor layer having a crystal region and a second oxide semiconductor layer crystal-grown from the crystal region of the first oxide semiconductor layer are used as the oxide semiconductor layer. Will be described in detail. In the following, a top gate type transistor will be described as an example, but the transistor configuration does not have to be limited to the top gate type.

First, the insulating layer 302 is formed on the lower substrate 300. Then, a first oxide semiconductor layer is formed on the insulating layer 302, and a region including the surface of at least the first oxide semiconductor layer is crystallized by the first heat treatment to form the first oxide semiconductor layer. It forms 304 (see Figure 28 (A)).

Here, the lower layer substrate 300 refers to the substrate on which the lower transistor 160 and the like are formed in the above embodiment. For the details, the above embodiment can be taken into consideration. The flatness of the surface of the lower layer substrate 300 should be given particular importance in the present embodiment. This is because the flatness of the surface is an indispensable factor for uniform crystal growth. To obtain a preferable crystalline oxide semiconductor layer, the height difference of the surface should be 1 nm or less, preferably 0.2 nm or less, or the root mean square (RMS) of the surface roughness should be 0.5 nm or less, preferably 0.1 nm or less. It is good to say.

The insulating layer 302 functions as a base, and can be formed in the same manner as the insulating layer 168 and the protective insulating layer 144 in the previous embodiment. For details, the above embodiment may be taken into consideration. It is desirable that the insulating layer 302 be formed so as not to contain hydrogen or water as much as possible.

The first oxide semiconductor layer 304 can be formed in the same manner as the oxide semiconductor layer 206 in the previous embodiment. For details of the first oxide semiconductor layer 304 and the film forming method thereof, the above-described embodiment may be referred to. However, in the present embodiment, since the first oxide semiconductor layer is intentionally crystallized by the first heat treatment, the first oxide semiconductor layer 304 is formed by using a metal oxide target in which crystallization is likely to occur. It is desirable to form. For example, ZnO. Further, even if it is an In-Ga-Zn-O oxide, for example, an oxide having a high concentration of Zn is easily crystallized, and the ratio of Zn to the metal element (In, Ga, Zn) is 60% or more. Is preferable for use for this purpose. The thickness of the first oxide semiconductor layer 304 is preferably 3 nm or more and 15 nm or less. In this embodiment, the thickness is 5 nm as an example. However, since the appropriate thickness differs depending on the oxide semiconductor material to be applied, the application of the semiconductor device, etc., the thickness may be selected according to the material to be used, the application, and the like.

The temperature of the first heat treatment is 450 ° C or higher and 850 ° C or lower, preferably 550 ° C or higher and 750 ° C or lower. The heat treatment time is preferably 1 minute or more and 24 hours or less. The temperature and time differ depending on the type and composition ratio of the oxide semiconductor. Further, it is desirable that the atmosphere of the first heat treatment is an atmosphere that does not contain hydrogen, water, or the like. For example, it can be a nitrogen, oxygen, noble gas (helium, neon, argon, etc.) atmosphere with sufficient water removed.

As the heat treatment apparatus, in addition to the electric furnace, an apparatus that heats the object to be processed by heat conduction from a medium such as heated gas or heat radiation can be used. For example, an RTA (Rapid Thermal Anneal) device such as a GRTA (Gas Rapid Thermal Anneal) device or an LRTA (Lamp Rapid Thermal Anneal) device can be used. The LRTA device is a device that heats an object to be processed by radiating light (electromagnetic waves) emitted from lamps such as halogen lamps, metal halide lamps, xenon arc lamps, carbon arc lamps, high-pressure sodium lamps, and high-pressure mercury lamps. The GRTA device is a device that performs heat treatment using a high-temperature gas. As the gas, a rare gas such as argon or an inert gas such as nitrogen that does not react with the object to be treated by heat treatment is used.

The region including the surface of at least the first oxide semiconductor layer is crystallized by the above-mentioned first heat treatment. The crystal region is a region formed by the progress of crystal growth from the surface of the first oxide semiconductor layer toward the inside of the first oxide semiconductor layer. The crystal region may include plate-like crystals having an average thickness of 2 nm or more and 10 nm or less. Further, the crystal region may include a crystal having an ab plane substantially parallel to the surface of the oxide semiconductor layer and the c-axis oriented in a direction substantially perpendicular to the surface. Here, substantially parallel means a state within ± 10 ° from the parallel direction, and substantially vertical means a state within ± 10 ° from the vertical direction.

Further, it is desirable to form a crystal region by the first heat treatment and remove hydrogen (including water and hydroxyl groups) in the first oxide semiconductor layer. When removing hydrogen, etc., perform the first heat treatment in a nitrogen, oxygen, or noble gas (helium, neon, argon, etc.) atmosphere with a purity of 6N (99.9999%) or more (that is, the concentration of impurities is 1ppm or less). Good to do. More preferably, the atmosphere has a purity of 7N (99.99999%) or more (that is, an impurity concentration of 0.1ppm or less). Also, H₂In ultra-dry air with O of 20 ppm or less, preferably H₂The first heat treatment may be performed in ultra-dry air having O of 1 ppm or less.

Further, it is desirable that the crystal region is formed by the first heat treatment and oxygen is supplied to the first oxide semiconductor layer. For example, oxygen can be supplied to the first oxide semiconductor layer by changing the atmosphere of the heat treatment to an oxygen atmosphere or the like.

In the first embodiment, as the first heat treatment, a heat treatment at 700 ° C. for 1 hour is performed in a nitrogen atmosphere to remove hydrogen and the like from the oxide semiconductor layer, and then the atmosphere is switched to an oxygen atmosphere. Oxygen is supplied to the inside of the oxide semiconductor layer. Since the main purpose of the first heat treatment is to form a crystal region, it is possible to separately perform treatments for the purpose of removing hydrogen and the like and supplying oxygen. For example, it is possible to perform a heat treatment for removing hydrogen or the like, a heat treatment for supplying oxygen, and then a heat treatment for crystallization.

By such a first heat treatment, a first oxide semiconductor layer 304 having a crystal region, hydrogen (including water and hydroxyl groups) is removed, and oxygen is supplied is obtained.

Next, the second oxide semiconductor layer 305 is formed on the first oxide semiconductor layer 304 having a crystal region at least in the region including the surface (see FIG. 28 (B)).

The second oxide semiconductor layer 305 can be formed in the same manner as the oxide semiconductor layer 206 in the previous embodiment. For details of the second oxide semiconductor layer 305 and the film forming method thereof, the above-described embodiment may be referred to. However, it is desirable that the second oxide semiconductor layer 305 is formed thicker than the first oxide semiconductor layer 304. Further, it is desirable to form the second oxide semiconductor layer 305 so that the sum of the thicknesses of the first oxide semiconductor layer 304 and the second oxide semiconductor layer 305 is 3 nm or more and 50 nm or less. Since the appropriate thickness varies depending on the oxide semiconductor material to be applied, the application of the semiconductor device, etc., the thickness may be selected according to the material to be used, the application, and the like.

For the second oxide semiconductor layer 305, a material having the same main component as that of the first oxide semiconductor layer 304 and having a close lattice constant after crystallization (a lattice constant mismatch of 1% or less) is used. Is desirable. This is because when materials having the same main component are used, crystal growth using the crystal region of the first oxide semiconductor layer 304 as a seed is likely to proceed in the crystallization of the second oxide semiconductor layer 305. Further, when the same main component material is used, the interfacial physical characteristics and electrical properties are also improved.

When a desired film quality can be obtained by crystallization, the second oxide semiconductor layer 305 may be formed by using a material having a main component different from that of the material of the first oxide semiconductor layer 304.

Next, the second oxide semiconductor layer 305 is subjected to a second heat treatment, and crystal growth is performed using the crystal region of the first oxide semiconductor layer 304 as a seed to form the second oxide semiconductor layer 306 (. See Figure 28 (C))).

The temperature of the second heat treatment is 450 ° C or higher and 850 ° C or lower, preferably 600 ° C or higher and 700 ° C or lower. The heating time of the second heat treatment is 1 minute or more and 100 hours or less, preferably 5 hours or more and 20 hours or less, and typically 10 hours. Even in the second heat treatment, it is desirable that the heat treatment atmosphere does not contain hydrogen, water, or the like.

The details of the atmosphere and the effect of the second heat treatment are similar to those of the first heat treatment. Further, the heat treatment apparatus that can be used is the same as in the case of the first heat treatment. For example, by making the inside of the furnace a nitrogen atmosphere when the temperature rises in the second heat treatment and the oxygen atmosphere inside the furnace when cooling, hydrogen and the like can be removed in the nitrogen atmosphere and oxygen can be supplied in the oxygen atmosphere. it can.

By performing the second heat treatment as described above, crystal growth is allowed to proceed from the crystal region formed on the first oxide semiconductor layer 304 to the entire second oxide semiconductor layer 305, and the second oxide is formed. The semiconductor layer 306 can be formed. Further, hydrogen (including water and hydroxyl groups) and the like are removed, and the second oxide semiconductor layer 306 to which oxygen is supplied can be formed. Further, the second heat treatment can enhance the orientation of the crystal region of the first oxide semiconductor layer 304.

For example, when an In-Ga-Zn-O-based oxide semiconductor material is used for the second oxide semiconductor layer 306, the second oxide semiconductor layer 306 is the InGaO.₃(ZnO)_mCrystals represented by (m&gt; 0 and not natural numbers) and In₂Ga₂ZnO₇It may contain crystals represented by (In: Ga: Zn: O = 2: 2: 1: 7). By the second heat treatment, such a crystal is oriented so that its c-axis is oriented substantially perpendicular to the surface of the second oxide semiconductor layer 306.

Here, the above-mentioned crystal contains any one of In, Ga, and Zn, and can be regarded as a laminated structure of a plurality of layers parallel to the a-axis (a-axis) and the b-axis (b-axis). Specifically, the above-mentioned crystal has a structure in which a layer containing In and a layer not containing In (a layer containing Ga or Zn) are laminated in the c-axis direction.

In-Ga-Zn-O-based oxide semiconductor crystals have good conductivity in the direction parallel to the In-containing layer, that is, the a-axis and the b-axis. This is because in In-Ga-Zn-O-based oxide semiconductor crystals, electrical conduction is mainly controlled by In, and one In 5s orbital overlaps with an adjacent In In 5s orbital. , Due to the formation of a carrier path.

Further, in the case of a structure in which the first oxide semiconductor layer 304 has an amorphous region at the interface with the insulating layer 302, the surface of the first oxide semiconductor layer 304 is subjected to the second heat treatment. Crystal growth may proceed from the formed crystal region toward the lower side of the first oxide semiconductor layer, and the amorphous region may be crystallized. The amorphous region may remain depending on the material constituting the insulating layer 302, the conditions of heat treatment, and the like.

When an oxide semiconductor material having the same main component is used for the first oxide semiconductor layer 304 and the second oxide semiconductor layer 305, as shown in FIG. 28 (C), the first oxide semiconductor layer 304 and the oxide semiconductor layer 304 , The second oxide semiconductor layer 306 may have the same crystal structure. Therefore, as shown by the dotted line in FIG. 28 (C), the boundary between the first oxide semiconductor layer 304 and the second oxide semiconductor layer 306 cannot be discriminated, and the boundary between the first oxide semiconductor layer 304 and the second oxide semiconductor layer 304 cannot be discriminated. In some cases, the oxide semiconductor layer 306 of the above can be regarded as the same layer.

Next, the first oxide semiconductor layer 304 and the second oxide semiconductor layer 306 are processed by a method such as etching using a mask, and the island-shaped first oxide semiconductor layer 304a and the second oxide are oxidized. The product semiconductor layer 306a is formed (see FIG. 28 (D)).

Either dry etching or wet etching may be used for etching the first oxide semiconductor layer 304 and the second oxide semiconductor layer 306. Of course, both can be used in combination. Etching conditions (etching gas, etching solution, etching time, temperature, etc.) are appropriately set according to the material so that the oxide semiconductor layer can be etched into a desired shape. The etching of the first oxide semiconductor layer 304 and the second oxide semiconductor layer 306 can be performed in the same manner as the etching of the oxide semiconductor layer in the previous embodiment. For details, the above embodiment may be taken into consideration.

It is desirable that the region of the oxide semiconductor layer that becomes the channel formation region has a flat surface. For example, the height difference on the surface of the second oxide semiconductor layer is preferably 1 nm or less (preferably 0.2 nm or less) in the region (channel formation region) overlapping with the gate electrode.

Next, the conductive layer is formed so as to be in contact with the second oxide semiconductor layer 306a. The conductive layer is then selectively etched to form a source or drain electrode 308a and a source or drain electrode 308b (see FIG. 28 (D)). The source electrode or drain electrode 308a and the source electrode or drain electrode 308b can be formed in the same manner as the source electrode or drain electrode 142a and the source electrode or drain electrode 142b in the previous embodiment. For details, the above embodiment may be taken into consideration.

Further, in the step shown in FIG. 28 (D), a crystal layer in contact with the source electrode or drain electrode 308a and the source electrode or drain electrode 308b on the side surfaces of the first oxide semiconductor layer 304a and the second oxide semiconductor layer 306a. May be in an amorphous state.

Next, the gate insulating layer 312 in contact with a part of the second oxide semiconductor layer 306a is formed. The gate insulating layer 312 can be formed by using a CVD method, a sputtering method, or the like. Then, the gate electrode 314 is formed on the gate insulating layer 312 in a region overlapping the first oxide semiconductor layer 304a and the second oxide semiconductor layer 306a. Then, the interlayer insulating layer 316 and the interlayer insulating layer 318 are formed on the gate insulating layer 312 and the gate electrode 314 (see FIG. 28 (E)). The gate insulating layer 312, the gate electrode 314, the interlayer insulating layer 316, and the interlayer insulating layer 318 can be formed in the same manner as the gate insulating layer in the previous embodiment. For details, the above embodiment may be taken into consideration.

After the formation of the gate insulating layer 312, it is desirable to perform a third heat treatment in an inert gas atmosphere or an oxygen atmosphere. The temperature of the third heat treatment is 200 ° C or higher and 450 ° C or lower, preferably 250 ° C or higher and 350 ° C or lower. For example, heat treatment may be performed at 250 ° C. for 1 hour in an atmosphere containing oxygen. By performing the third heat treatment, it is possible to reduce variations in the electrical characteristics of the transistor. When the gate insulating layer 312 is an insulating layer containing oxygen, oxygen is supplied to the second oxide semiconductor layer 306a to reduce the oxygen deficiency of the second oxide semiconductor layer 306a, and i-type (intrinsic). It is also possible to form an oxide semiconductor layer as close as possible to a semiconductor) or i-type.

In the present embodiment, the third heat treatment is performed after the formation of the gate insulating layer 312, but the timing of the third heat treatment is not limited to this. Further, when oxygen is supplied to the second oxide semiconductor layer by another treatment such as the second heat treatment, the third heat treatment may be omitted.

The gate electrode 314 can be formed by forming a conductive layer on the gate insulating layer 312 and then selectively patterning the conductive layer. For details, the description regarding the gate electrode of the previous embodiment can be referred to.

The interlayer insulating layer 316 and the interlayer insulating layer 318 can be formed by using a PVD method, a CVD method, or the like. Further, it can be formed by using a material containing an inorganic insulating material such as silicon oxide, silicon oxynitride, silicon nitride, hafnium oxide, aluminum oxide, and tantalum pentoxide. In the present embodiment, the interlayer insulating layer 316 and the interlayer insulating layer 318 are laminated, but one aspect of the disclosed invention is not limited to this. It may be one layer or a laminated structure of three or more layers.

It is desirable that the interlayer insulating layer 318 is formed so that its surface is flat. This is because by forming the interlayer insulating layer 318 so that the surface becomes flat, electrodes, wiring, and the like can be suitably formed on the interlayer insulating layer 318.

As described above, the transistor 350 using the first oxide semiconductor layer 304a and the second oxide semiconductor layer 306a crystal grown from the crystal region of the first oxide semiconductor layer 304a is completed.

The transistor 350 shown in FIG. 28 (E) has a first oxide semiconductor layer 304a provided on the lower substrate 300 via an insulating layer 302 and a second oxide semiconductor layer 304a provided on the first oxide semiconductor layer 304a. Oxide semiconductor layer 306a, source electrode or drain electrode 308a electrically connected to the second oxide semiconductor layer 306a, source electrode or drain electrode 308b, and second oxide semiconductor layer 306a, source electrode or drain. On the gate insulating layer 312 covering the electrode 308a, the source electrode or the drain electrode 308b, the gate electrode 314 on the gate insulating layer 312, the interlayer insulating layer 316 on the gate insulating layer 312 and the gate electrode 314, and on the interlayer insulating layer 316. It has an interlayer insulating layer 318.

In the transistor 350 shown in the present embodiment, since the first oxide semiconductor layer 304a and the second oxide semiconductor layer 306a are highly purified, the hydrogen concentration thereof is 5 × 10.¹⁹/cm³Below, preferably 5x10¹⁸/cm³Below, more preferably 5x10¹⁷/cm³Below, more preferably 1x10¹⁶/cm³Will be less than. The carrier density of the oxide semiconductor layer is the carrier density (1 × 10) in a general silicon wafer.¹⁴/cm³A sufficiently low value (eg 1x10) compared to the degree)¹²/cm³Less than, preferably 1x10¹¹/cm³Less than). As a result, the off-current becomes sufficiently small. For example, drain voltage V_DIs + 1V or + 10V and the gate voltage V_GIn the range of -5V to -20V, the off-current at room temperature is 1x10.^-13A or less. Further, the above-mentioned transistor has a normally-off transistor characteristic. Therefore, the off-current, that is, the leakage current when the voltage between the gate and the source electrode is almost 0 is significantly smaller than that of the transistor using silicon. For example, the unit channel width leakage current at room temperature is 10 aA / μm or less.

By using the first oxide semiconductor layer 304a and the second oxide semiconductor layer 306a that have been purified and purified in this way, the off-current of the transistor can be sufficiently reduced.

Further, in the present embodiment, as the oxide semiconductor layer, the first oxide semiconductor layer 304a having a crystal region and the second oxide semiconductor obtained by crystal-growing from the crystal region of the first oxide semiconductor layer 304a. Since the layer 306a is used, the mobility of the electric field effect can be improved and a transistor having good electrical characteristics can be realized.

In the present embodiment, the case where the transistor 350 is used as the transistor 402 shown in the previous embodiment has been described, but it is not necessary to interpret the disclosed invention in a limited manner. For example, the transistor 350 shown in the present embodiment has a first oxide semiconductor layer 304a having a crystal region and a second oxide semiconductor layer 306a in which crystals are grown from the crystal region of the first oxide semiconductor layer 304a. Since it has a good electric field effect mobility, it is possible to use an oxide semiconductor for all the transistors including the transistors constituting the integrated circuit. In such a case, it is not necessary to have a laminated structure as shown in the previous embodiment. In this case, for example, it is possible to form a semiconductor device using a substrate such as a glass substrate.

As described above, the configurations and methods shown in the present embodiment can be appropriately combined with the configurations and methods shown in other embodiments.

(Embodiment 13) In the present embodiment, an example of an electronic device equipped with a semiconductor device using the non-volatile latch circuit obtained in the previous embodiment will be described with reference to FIG. 29. The electronic device equipped with the semiconductor device using the non-volatile latch circuit obtained in the above embodiment has excellent characteristics that have never been seen before. Therefore, it is possible to provide an electronic device having a new configuration by using a semiconductor device using the non-volatile latch circuit. The semiconductor device using the non-volatile latch circuit according to the previous embodiment is integrated and mounted on a circuit board or the like, and is mounted inside each electronic device.

FIG. 29A is a notebook-type personal computer including a semiconductor device using the non-volatile latch circuit according to the previous embodiment, and is composed of a main body 1301, a housing 1302, a display unit 1303, a keyboard 1304, and the like. Has been done. By applying the semiconductor device according to the disclosed invention to a notebook personal computer, it is possible to provide a notebook personal computer having excellent performance.

FIG. 29B shows a personal digital assistant (PDA) including a semiconductor device using a non-volatile latch circuit according to the previous embodiment, and the main body 1311 has a display unit 1313 and an external interface 1315 for operation. Button 1314 etc. are provided. There is also a stylus 1312 as an accessory for operation. By applying the semiconductor device according to the disclosed invention to a personal digital assistant (PDA), it is possible to provide a personal digital assistant (PDA) having excellent performance.

FIG. 29 (C) shows an electronic book 1320 as an example of an electronic paper including a semiconductor device using the non-volatile latch circuit according to the previous embodiment. The electronic book 1320 is composed of two housings, a housing 1321 and a housing 1323. The housing 1321 and the housing 1323 are integrated by a shaft portion 1337, and the opening / closing operation can be performed with the shaft portion 1337 as an axis. With such a configuration, the electronic book 1320 can be used like a paper book.

The display unit 1325 is incorporated in the housing 1321, and the display unit 1327 is incorporated in the housing 1323. The display unit 1325 and the display unit 1327 may be configured to display a continuous screen or may be configured to display different screens. By displaying different screens, for example, the text is displayed on the right display unit (display unit 1325 in Fig. 29 (C)), and the image is displayed on the left display unit (display unit 1327 in Fig. 29 (C)). Can be displayed.

Further, FIG. 29 (C) shows an example in which the housing 1321 is provided with an operation unit and the like. For example, the housing 1321 includes a power supply 1331, operation keys 1333, a speaker 1335, and the like. Pages can be sent using the operation key 1333. A keyboard, a pointing device, or the like may be provided on the same surface as the display unit of the housing. Further, the back or side surface of the housing may be provided with an external connection terminal (earphone terminal, USB terminal, or a terminal that can be connected to various cables such as an AC adapter and a USB cable), a recording medium insertion part, and the like. .. Further, the electronic book 1320 may be configured to have a function as an electronic dictionary.

Further, the electronic book 1320 may be configured to be able to transmit and receive information wirelessly. It is also possible to purchase and download desired book data or the like from an electronic book server wirelessly.

The electronic paper can be applied to any field as long as it displays information. For example, in addition to electronic books, it can be applied to posters, in-car advertisements of vehicles such as trains, and display on various cards such as credit cards. By applying the semiconductor device according to the disclosed invention to electronic paper, it is possible to provide electronic paper having excellent performance.

FIG. 29 (D) is a mobile phone including a semiconductor device using the non-volatile latch circuit according to the previous embodiment. The mobile phone is composed of two housings, a housing 1340 and a housing 1341. The housing 1341 includes a display panel 1342, a speaker 1343, a microphone 1344, a pointing device 1346, a camera lens 1347, an external connection terminal 1348, and the like. Further, the housing 1340 includes a solar cell 1349 for charging the mobile phone, an external memory slot 1350, and the like. In addition, the antenna is built in the housing 1341.

The display panel 1342 has a touch panel function, and in FIG. 29 (D), a plurality of operation keys 1345 displayed as images are shown by dotted lines. The mobile phone is equipped with a booster circuit for boosting the voltage output from the solar cell 1349 to the voltage required for each circuit. Further, in addition to the above configuration, a non-contact IC chip, a small recording device, and the like can be built in.

The display direction of the display panel 1342 changes as appropriate according to the usage pattern. In addition, since the camera lens 1347 is provided on the same surface as the display panel 1342, it is possible to make a videophone call. The speaker 1343 and microphone 1344 are capable of videophone, recording, playback, etc., as well as voice calls. Further, the housing 1340 and the housing 1341 can be slid and changed from the unfolded state to the overlapping state as shown in FIG. 29 (D), and the miniaturization suitable for carrying is possible.

The external connection terminal 1348 can be connected to various cables such as an AC adapter and USB cable, enabling charging and data communication. In addition, a recording medium can be inserted into the external memory slot 1350 to support storage and movement of a larger amount of data. Further, in addition to the above functions, an infrared communication function, a television reception function, and the like may be provided. By applying the semiconductor device according to the disclosed invention to a mobile phone, it is possible to provide a mobile phone having excellent performance.

FIG. 29 (E) is a digital camera including a semiconductor device using the non-volatile latch circuit according to the previous embodiment. The digital camera is composed of a main body 1361, a display unit (A) 1367, an eyepiece unit 1363, an operation switch 1364, a display unit (B) 1365, a battery 1366, and the like. By applying the semiconductor device according to the disclosed invention to a digital camera, it is possible to provide a digital camera having excellent performance.

FIG. 29 (F) is a television device including a semiconductor device using the non-volatile latch circuit according to the previous embodiment. In the television device 1370, the display unit 1373 is incorporated in the housing 1371. The display unit 1373 can display an image. Here, the configuration in which the housing 1371 is supported by the stand 1375 is shown.

The operation of the television device 1370 can be performed by the operation switch provided in the housing 1371 or the separate remote control operation device 1380. The operation keys 1379 provided in the remote controller 1380 can be used to control the channel and volume, and the image displayed on the display unit 1373 can be operated. Further, the remote controller 1380 may be provided with a display unit 1377 for displaying information output from the remote controller 1380.

The television device 1370 is preferably configured to include a receiver, a modem, and the like. The receiver can receive general television broadcasts. In addition, by connecting to a wired or wireless communication network via a modem, information communication is performed in one direction (from sender to receiver) or in two directions (between sender and receiver, or between recipients, etc.). It is possible. By applying the semiconductor device according to the disclosed invention to a television device, it is possible to provide a television device having excellent performance.

The configuration, method, etc. shown in this embodiment can be used in appropriate combination with the configuration, method, etc. shown in other embodiments.

100 Substrate 102 Protective layer 104 Semiconductor region 106 Element separation insulation layer 108a Gate insulation layer 110a Gate electrode 110b Electrode 112 Insulation layer 114 Impure region 116 Channel formation region 118 Sidewall insulation layer 120 High concentration impurity region 122 Metal layer 124 Metal compound region 126 Interlayer Insulation Layer 128 Interlayer Insulation Layer 130a Source or Drain Electrode 130b Source or Drain Electrode 130c Electrode 132 Insulation Layer 134 Conductive Layer 136a Electrode 136b Electrode 136c Electrode 136d Gate Electrode 138 Gate Insulation Layer 140 Oxide Semiconductor Layer 142 Conductive Layer 142a Source Electrode or drain electrode 142b Source electrode or drain electrode 144 Protective insulation layer 146 Interlayer insulation layer 148 Conductive layer 150a Electrode 150b Electrode 150c Electrode 150d Electrode 150e Electrode 152 Insulation layer 154a Electrode 154b Electrode 154c Electrode 154d Electrode 154e Electrode 156 Insulation layer 158a Electrode 158b Electrode 158c Electrode 158d Electrode 160 Transistor 164 Insulation layer 164a Insulation layer 164b Insulation layer 166 Gate insulation layer 168 Insulation layer 170 Interlayer insulation layer 172 Lower substrate 202 Insulation layer 206 Oxide semiconductor layer 206a Oxide semiconductor layer 208a Source electrode or drain electrode 208b Source electrode or drain electrode 212 Gate insulation layer 214 Gate electrode 216 Interlayer insulation layer 218 Interlayer insulation layer 250 Transistor 300 Lower substrate 302 Insulation layer 304 Oxide semiconductor layer 304a Oxide semiconductor layer 305 Oxide semiconductor layer 306 Oxide semiconductor layer 306a Oxide semiconductor layer 308a Source electrode or drain electrode 308b Source electrode or drain electrode 312 Gate insulation layer 314 Gate electrode 316 Interlayer insulation layer 318 Interlayer insulation layer 350 Transistor 400 Latch circuit 400a Latch circuit 400b Latch circuit 401 Data holding unit 402 Transistor 402a Transistor 402b Transistor 404 Capacity 404a Capacity 404b Capacity 411 Latch part 412 First element 413 Second element 414 Wiring 415 Wiring 431 Switch 432 Switch 1301 Main body 1302 Housing 1303 Display 1304 Keyboard 1311 Main body 1312 Stylus 1313 Display 1314 Operation button 1315 External interface 1320 Electronic book 1321 Housing 1323 Housing 1325 Display 1327 Display 1331 Power supply 1333 Operation key 1335 Speaker 1337 Shaft 1340 Housing 1341 Housing 1342 Display panel 1343 Speaker 1344 Microphone 1345 Operation key 1346 Pointing device 1347 Camera lens 1348 External connection terminal 1349 Solar cell 1350 External memory slot 1361 Main unit 1363 Eyepiece 1364 Operation switch 1365 Display (B) 1366 Battery 1367 Display (A) 1370 TV John device 1371 Housing 1373 Display unit 1375 Stand 1377 Display unit 1379 Operation key 1380 Remote control operation machine