Process for fabricating dielectric capacitor

The present invention relates to a method for manufacturing a dielectric capacitor, and particularly to an improvement in the ferroelectricity thereof.

A conventional ferroelectric capacitor is shown in FIG. A silicon oxide layer 4 is formed on the silicon substrate 2. A lower electrode 6 made of platinum is provided on the lower electrode 6. Above the lower electrode 6, PZT (PbZr), which is a ferroelectric layer,_XTi_1-XO₃) A film 8 is provided, and an upper electrode 10 made of platinum is provided on the film 8. In this way, the ferroelectric capacitor is formed by the lower electrode 6, the PZT film 8, and the upper electrode 10.

Here, platinum is used as the lower electrode 6 for the following reasons. The PZT film 8 must be formed on the alignment film. This is because if it is formed on an amorphous film, it will not be oriented and the ferroelectricity will be impaired. On the other hand, the lower electrode 6 must be formed in a state of being insulated from the silicon substrate 2. Therefore, the silicon oxide layer 4 is formed on the silicon substrate 2. The silicon oxide layer 4 is amorphous. Generally, a film formed on an amorphous film becomes an unaligned film, but platinum has a property of forming an oriented film even on an amorphous film. For this reason, platinum is used as the lower electrode.

<p> However, the conventional ferroelectric capacitor as described above has the following problems.</p><p> Since platinum easily permeates oxygen, there is a problem that the ferroelectricity is lowered due to the escape of oxygen in the ferroelectric substance (PZT), aging, and repeated polarization reversal. That is, as shown in FIG. 30, oxygen in the ferroelectric substance may escape from between the columnar crystals of platinum.</p><p> Further, such a problem also occurs in a capacitor using a dielectric having a high dielectric constant.</p><p> An object of the present invention is to solve the above-mentioned problems and to provide a ferroelectric capacitor having less deterioration due to aged deterioration and repeated polarization reversal or a dielectric capacitor having a high dielectric constant.</p>

<p> The method for manufacturing a dielectric capacitor of the present invention includes a step of forming an insulating layer on a substrate, a step of forming an iridium layer composed of columnar polycrystals as a lower electrode on the substrate on which the insulating layer is formed, and the lower electrode. After the step of forming the oxide dielectric layer on the oxide dielectric layer and the step of forming the upper electrode on the oxide dielectric layer, and forming the iridium layer made of the columnar polycrystal as the lower electrode.<u style="single">, Before forming the oxide dielectric layer on the lower electrode</u>The step is characterized in that iridium oxide is formed on the surface of the iridium layer composed of the columnar polycrystal. In the present invention, the "capacitor" refers to a structure in which electrodes are provided on both sides of an insulator, and is a concept including a structure having this structure regardless of whether or not it is used for storing electricity. is there.</p><p> Desirably, a lower electrode having at least an iridium oxide layer, a dielectric layer formed on the lower electrode and composed of a ferroelectric substance or a dielectric having a high dielectric constant, an upper electrode formed on the dielectric layer. , Is equipped.</p><p> Desirably, the lower electrode is characterized by being composed of an iridium oxide layer formed by sputtering.</p><p> Desirably, a conductor layer having good crystal orientation is formed on the iridium oxide layer to form a lower electrode, and a ferroelectric layer is formed on the conductor layer. There is.</p><p> Desirably, the conductor layer is characterized by being a platinum layer.</p><p> Desirably, the conductor layer is characterized by being an iridium layer.</p><p> Desirably, the conductor layer is characterized by being an alloy layer of platinum and iridium.</p><p> Desirably, the lower electrode is formed on a silicon oxide layer formed on the substrate, and the lower electrode is characterized by having a bonding layer in contact with the silicon oxide layer.</p><p> Desirably, the lower electrode is characterized by being composed of an iridium layer and an iridium oxide layer formed on the iridium layer.</p><p> Desirably, the lower electrode is characterized in that it is formed by oxidizing the surface of the iridium layer.</p><p> Desirably, a conductor layer having good crystal orientation is formed on the iridium oxide layer to form a lower electrode, and a ferroelectric layer is formed on the conductor layer. There is.</p><p> Desirably, the conductor layer is characterized by being a platinum layer.</p><p> Desirably, the conductor layer is characterized by being an iridium layer.</p><p> Desirably, the conductor layer is characterized by being an alloy layer of platinum and iridium.</p><p> Desirably, the lower electrode is formed on a silicon oxide layer formed on the substrate, and the lower electrode is characterized by having a bonding layer in contact with the silicon oxide layer.</p><p> Desirably, a dielectric comprising a lower electrode, a dielectric layer formed on the lower electrode and composed of a strong dielectric or a dielectric having a high dielectric constant, and an upper electrode formed on the dielectric layer. The lower electrode of the capacitor is characterized in that it is formed by forming a conductive thin film having good crystal orientation on the surface of the iridium layer and then oxidizing it.</p><p> Desirably, the conductive thin film is characterized by being platinum.</p><p> Desirably, the conductive thin film is characterized by being an alloy of iridium and platinum.</p><p> Desirably, the upper electrode formed on the lower electrode, the lower electrode, and formed on the dielectric layer, the dielectric layer composed of a ferroelectric substance or a dielectric having a high dielectric constant, and having at least an iridium oxide layer. , Is equipped.</p><p> Desirably, the upper electrode is characterized by being composed of an iridium oxide layer formed by sputtering.</p><p> Desirably, the upper electrode is characterized by being composed of an iridium layer and an iridium oxide layer formed on the iridium layer.</p><p> Desirably, the upper electrode is characterized in that it is formed by oxidizing the surface of the iridium layer.</p><p> Desirably, it is formed on a lower electrode having at least an iridium oxide layer, a dielectric layer formed on a lower electrode and composed of a ferroelectric substance or a dielectric having a high dielectric constant, and at least oxidized. It comprises an upper electrode, which has an iridium layer.</p><p> The dielectric capacitor of the present invention has an iridium oxide layer and iridium on the lower electrode. Therefore, it is possible to prevent oxygen from escaping from the dielectric layer, and it is possible to suppress the secular change of the dielectric properties. That is, the iridium oxide layer does not have orientation regardless of whether the underlying layer is oriented, but when an iridium layer is further provided on the iridium oxide layer, the iridium layer has orientation. The dielectric layer formed on this upper layer is well oriented, and the current integrated value hardly changes, and good characteristics can be obtained. Further, since iridium is formed on the iridium oxide layer, the orientation of the ferroelectric layer can be improved while preventing the escape of oxygen. Furthermore, since the lead component in the ferroelectric layer does not penetrate toward the lower electrode, the imprint characteristics are improved. Further, preferably, the lower electrode is composed of an iridium layer formed on the surface of the substrate via a silicon oxide film and an iridium oxide layer formed on the iridium layer. Therefore, since the dielectric layer is formed on the lower electrode, the entire lower surface of the dielectric layer is in contact with the lower electrode, and the permeation of oxygen from the dielectric layer becomes a problem. , Iridium oxide is formed so as to fill the space between the columnar crystals of iridium. Therefore, the permeation of oxygen from the dielectric layer can be prevented extremely well. Therefore, it is possible to prevent the permeation of oxygen, and it is possible to provide a dielectric capacitor having excellent residual polarization characteristics. Further, in the dielectric capacitor of the present invention, an iridium layer composed of a substrate, a columnar crystal formed on an insulated surface on the substrate, and an oxidation formed between the columnar crystals by oxidation of the iridium layer. Since it has a lower electrode composed of an iridium layer, iridium oxide is formed so as to fill the space between the columnar crystals of iridium. Therefore, the permeation of oxygen from the dielectric layer can be prevented extremely well. Therefore, it is possible to prevent the permeation of oxygen, and it is possible to provide a dielectric capacitor having excellent residual polarization characteristics. In the dielectric capacitor of the present invention, the upper electrode has an iridium layer composed of columnar crystals and an upper electrode composed of an iridium layer formed between the columnar crystals by oxidation of the iridium layer. , Iridium oxide is formed so as to fill the space between the columnar crystals of iridium. Therefore, the permeation of oxygen from the dielectric layer can be prevented extremely well. Therefore, it is possible to prevent the permeation of oxygen, and it is possible to provide a dielectric capacitor having excellent residual polarization characteristics.</p><p> In the dielectric capacitor of the present invention, a conductive layer having good crystal orientation is provided on the iridium oxide layer, and the dielectric layer is provided on the conductive layer. Therefore, the orientation of the dielectric layer is improved, and the secular change of the dielectric properties can be suppressed.</p><p> In the dielectric capacitor of the present invention, an iridium layer is provided on the iridium oxide layer, and a dielectric layer is provided on the iridium layer. Therefore, the orientation of the dielectric layer is further improved, and the secular change of the dielectric properties can be suppressed.</p><p> The dielectric capacitor of the present invention is formed by providing a thin film conductor having good crystal orientation on the surface of iridium and then performing an oxidation treatment. Therefore, it is possible to prevent oxygen from escaping from the dielectric layer and to obtain a dielectric layer having good orientation. Therefore, the secular change of the dielectric property can be suppressed considerably.</p><p> The dielectric capacitor of the present invention has an iridium oxide layer on the upper electrode. Therefore, it is possible to prevent oxygen from escaping from the dielectric layer, and it is possible to suppress the secular change of the dielectric properties.</p><p> The dielectric capacitor of the present invention has an iridium oxide layer on both the upper electrode and the lower electrode. Therefore, it is possible to reliably prevent the escape of oxygen from the dielectric layer, and it is possible to suppress the secular change of the dielectric properties.</p><p> That is, it is possible to provide a dielectric capacitor having good ferroelectricity and high dielectric property.</p>

FIG. 1 shows the composition of a ferroelectric capacitor according to an embodiment of the present invention. A silicon oxide layer 4, a lower electrode 12, a ferroelectric film (ferroelectric layer) 8, and an upper electrode 15 are provided on the silicon substrate 2. The lower electrode 12 is formed of iridium oxide, and the upper electrode 15 is also formed of iridium oxide.

Figure 2 shows a comparison of the physical characteristics of platinum and iridium. As is clear from this table, the resistivity of iridium oxide is 49 × 10.^-6It is Ωcm, and there is no problem as an electrode material.

As shown in FIG. 30 of the conventional example, since platinum is a columnar crystal, it permeates oxygen in the ferroelectric film 8. In this example, iridium oxide is used as the lower electrode 12. Since the iridium oxide layer 12 is not a columnar crystal, it is difficult for oxygen to permeate. Therefore, the oxygen deficiency of the ferroelectric film 8 can be prevented. The same applies to the upper electrode 15. As a result, the ferroelectricity of the ferroelectric film 8 is improved. This point will be described in detail later together with the experimental data.

In the above embodiment, since both the lower electrode 12 and the upper electrode 15 are formed of iridium oxide, the permeation of oxygen can be reliably prevented. However, a certain effect can be obtained with only one of them. This point will also be described later.

The ferroelectric capacitor as described above can be used as a non-volatile memory in combination with the transistor 24, for example, as shown in FIG.

FIG. 4 shows a manufacturing process of a ferroelectric capacitor according to an embodiment of the present invention. The surface of the silicon substrate 2 is thermally oxidized to form the silicon oxide layer 4 (FIG. 4A). Here, the thickness of the silicon oxide layer 4 is set to 600 nm. Next, using iridium as a target, iridium oxide is formed on the silicon oxide layer 4 by reactive sputtering, and this is used as the lower electrode 12 (FIG. 4B). Here, it was formed to a thickness of 200 nm.

Next, a PZT film is formed as the ferroelectric layer 8 on the lower electrode 12 by the sol-gel method (FIG. 4C). Pb (CH) as a starting material₃COO)₂ 3H₂O, Zr (t-OC)₄H₉)₄, Ti (i-OC)₃H₇)₄The mixed solution of was used. After spin-coating this mixed solution, it was dried at 150 degrees Celsius (Celsius, the same applies hereinafter), and pre-baked at 400 degrees for 30 seconds in a dry air atmosphere. After repeating this 5 times, O₂Heat treatment of 700 degrees or more was performed in the atmosphere. In this way, the 250 nm ferroelectric layer 8 was formed. In addition, here, PbZr_xTi_1-xO₃In, x is 0.52 (hereinafter referred to as PZT (52, 48)) to form a PZT film.

Further, iridium oxide is formed on the ferroelectric layer 8 by reactive sputtering to form an upper electrode 15 (FIG. 4D). Here, it was formed to a thickness of 200 nm. In this way, a ferroelectric capacitor can be obtained.

FIGS. 5 and 6 show fatigue of the remanent polarization Pr when a ferroelectric capacitor is formed by using PZT (52/48) as the ferroelectric film 8. The test was carried out by applying a voltage between points a and b with the structure shown in Fig. 8. Voltages of 5V and -5V as shown in FIG. 7 were applied between the upper electrode 15 and the lower electrode 12, and the deterioration of the remanent polarization Pr was measured. The application of 5V and -5V voltages was defined as one cycle. The voltage was applied at a frequency of 500 KHz.

The vertical axis of FIGS. 5 and 6 represents the value of Pr / Po when the initial remanent polarization is Po and the remanence after fatigue is Pr. That is, the larger this value is, the more remarkable the deterioration is. The horizontal axis represents how many cycles the voltage of FIG. 7 was repeatedly applied. In the figure, the curve 50 shows the upper electrode 15 and the lower electrode 12 both made of iridium oxide, the curve 52 shows the upper electrode 15 made of platinum, and the curve 54 shows the upper electrode 15 made of iridium oxide. This is a characteristic change when the lower electrode 12 is made of platinum with iridium oxide and when both the upper electrode 15 and the lower electrode 12 are made of platinum.

As is clear from this figure, it is clear that the deterioration of the remanent polarization Pr is considerably improved when either the upper electrode 15 or the lower electrode 12 is composed of iridium oxide. In particular, if both the upper electrode 15 and the lower electrode 12 are composed of iridium oxide, 10¹⁰It is clear that there is almost no deterioration up to the cycle.

By the way, iridium oxide has no orientation regardless of whether or not the underlying layer is oriented. Therefore, the ferroelectric film 8 formed on the iridium oxide is also not oriented.

In order to verify that iridium oxide does not have orientation regardless of the orientation of the underlying layer, the following test was conducted. The characteristics of a ferroelectric capacitor in which iridium oxide was directly formed as a lower electrode 12 on a silicon substrate 2 and a ferroelectric capacitor in which iridium oxide was formed as a lower electrode 12 on a silicon oxide layer 4 were compared. .. FIG. 9 shows the hysteresis characteristic. FIG. 9A shows a case where the lower electrode 12 is formed on the silicon oxide layer 4, and FIG. 9B shows a case where iridium oxide is formed directly on the silicon substrate 2 as the lower electrode 12. As is clear from this graph, it is shown that the characteristics of the ferroelectric film 8 are the same regardless of whether the underlying layer of iridium oxide is silicon or silicon oxide. It seems that this is because iridium oxide has no orientation regardless of whether or not the underlying layer is oriented.

If the iridium oxide layer of the lower electrode 12 is not oriented, the orientation of the ferroelectric film 8 formed on the layer is also deteriorated. Therefore, if the orientation of the ferroelectric layer 8 is improved while using the iridium oxide layer, the fatigue characteristics of the remanent polarization Pr are further improved.

For this purpose, a platinum layer may be formed on the iridium oxide layer to form the lower electrode 12. Figure 10A shows the change in characteristics when this is done. In this graph, the vertical axis represents the magnitude of polarization, and the horizontal axis represents the application cycle of the same voltage as in FIG. In addition, this graph shows changes in the features Pr, Pmax, P, and N of the hysteresis characteristics shown in FIG. 10B. As is clear from the graph, the deterioration of the characteristics is further improved by providing the platinum layer on the iridium oxide layer. That is, 10¹¹Almost no deterioration has occurred until the cycle.

In addition, instead of the platinum layer, a conductor layer having good orientation such as an iridium layer or an alloy of platinum and iridium may be provided (the structure shown in FIG. 27 may be used as described later). In particular, for an alloy of platinum and iridium, the lattice constant can be selected by changing the compounding ratio, and it is easy to match the lattice constant with the ferroelectric layer.

In FIG. 11, PZT (52/48) is used as the ferroelectric layer 8 and Pt is used as the lower electrode 12._xIr_1-xThe change in the remanent polarization Pr and the coercive electric field Ec when the composition ratio x of platinum and iridium is changed is shown in the graph. As is clear from this figure, the residual polarization Pr is higher when the alloy with iridium is used as the lower electrode 12 than when only platinum is used (when x = 1.0). It is clear to show. That is, it can be said that the ferroelectricity is improved. Remarkable improvement in characteristics was obtained in the range of 0% to 50% of platinum, and extremely excellent characteristics were obtained especially in a mixing ratio of 20% to 30% with a peak of about 25% of platinum. Therefore, if the above alloy is formed on the iridium oxide layer, the ferroelectric film 8 having excellent properties can be obtained.

Even when a conductive layer is formed on the iridium oxide layer and used as an electrode, the iridium oxide layer is formed on both the upper and lower electrodes 15 and 12 as in the case of FIGS. 5 and 6. Is preferable.

12 and 13 show the hysteresis characteristics when the iridium oxide layer and the iridium layer are used for the upper electrode 15 (FIGS. 12A and 13A), and the hysteresis characteristics when only the iridium layer is used for the upper electrode 15 (FIG. 12B). , Fig. 13B) is shown. In both cases, the lower electrode was formed by an iridium oxide layer and an iridium layer. The initial characteristics (Fig. 12A, Fig. 12B) are the same for both, but the characteristics after applying the pulse 108 times (cycles) (Fig. 13A, Fig. 13B) clearly show that the upper electrode 15 also has an iridium oxide layer. It is better to use the iridium layer. This is also considered to be an effect of preventing the escape of oxygen by the iridium oxide layer.

There was no difference in the secular change characteristics of the residual polarization Pr and coercive electric field Ec as described above between the case where platinum was provided on the iridium oxide layer and the case where iridium was provided. However, when a pulse in a fixed direction is continuously applied to the ferroelectric layer 8 or when the ferroelectric layer 8 is held in a polarized state in a fixed direction for a long time, there is a difference in the imprint characteristic in which the polarization characteristic becomes stiff.

FIG. 14 shows the characteristics of the ferroelectric capacitor when platinum is provided on the iridium oxide layer to form the lower electrode 12. This graph shows the case where a voltage different from the polarization direction is applied to the ferroelectric capacitor (ferroelectric film 8) in the polarized state (inversion mode shown in FIG. 15A) and the case where the same voltage as the polarization direction is applied. It shows the temporal change of the current (current per unit area) of (non-inverting mode shown in FIG. 15B). It can be seen that a larger current flows in the reverse mode.

This characteristic is utilized when a ferroelectric capacitor is used as a memory. That is, it is used to determine the magnitude of the integrated value of the current when a voltage is applied by comparing it with the threshold value and read out the recorded information. Therefore, as the period of use elapses, the current integral value in the inversion mode QP decreases (that is, approaches the threshold value), and the current integral value in the non-inverted mode increases (that is, the threshold value). If it approaches), erroneous reading may occur.

FIG. 16 shows 3 × 10 pulses in the same direction on the ferroelectric film 8 (when both the upper electrode 15 and the lower electrode 12 are formed by providing platinum on the iridium oxide layer).⁹The current in the inversion and non-inversion modes after application is shown. As is clear from the results of this experiment, the integrated current value in the inversion mode QP + decreases and is almost equal to the integral value in the first non-inversion mode QU-.

FIG. 17 shows the change in the integrated current value in the above case. The horizontal axis is the pulse application cycle (number of times), and the vertical axis is the current integral value. As you can see from the graph, 10⁴It can be seen that the current integral value changes significantly from around the time when it exceeds the number of times.

FIG. 18 shows changes in the current integral value of the ferroelectric film 8 when both the upper electrode 15 and the lower electrode 12 are formed by providing the iridium layer on the iridium oxide layer. As is clear from the graph, the current integral value hardly changes, and good characteristics are selected. That is, it was clarified that the electrode having iridium formed on iridium oxide is superior to the electrode having platinum formed on iridium oxide in terms of the above-mentioned imprint characteristics.

FIG. 19 shows the results of analyzing the element content in each layer of the ferroelectric capacitor used in the above experiment. FIG. 19A shows the case where platinum is formed on iridium oxide, and FIG. 19B shows the case where iridium is formed on iridium oxide. The horizontal axis shows the depth from the surface of the upper electrode, and the vertical axis shows the content of each element.

What is clear from this graph is that in the case of FIG. 19A, the lead (Pb) component in the ferroelectric layer 8 has penetrated to the platinum (Pt) of the lower electrode. On the other hand, in the case of FIG. 19B, the lead (Pb) component of 8 in the ferroelectric substance hardly penetrates toward the lower electrode. This seems to affect the imprint characteristics as described above.

FIG. 20 shows the structure of a ferroelectric capacitor according to another embodiment of the present invention. In this embodiment, a titanium layer (5 nm) is provided as a bonding layer 30 between the lower electrode 12 and the silicon oxide layer 4. Generally, the adhesion between iridium oxide and silicon oxide is not very good. Therefore, the alloy layer may be partially peeled off and the ferroelectric properties may be deteriorated. In particular, the higher the ratio of iridium in the alloy, the more remarkable this becomes. Therefore, in this embodiment, a titanium layer having good adhesion to the silicon oxide layer 4 is provided as the bonding layer 30. This improves the ferroelectric properties. The titanium layer may be formed by sputtering.

In the above embodiment, the titanium layer is used as the bonding layer 30, but any material may be used as long as it is a material for improving the bonding property. For example, a platinum layer may be used.

In each of the above examples, PZT is used as the ferroelectric film 8, but any oxide ferroelectric film may be used. For example, Ba₄Ti₃O₁₂May be used.

A capacitor according to another embodiment of the present invention is shown in FIG. In this embodiment, the dielectric layer 90 having a high dielectric constant is used instead of the ferroelectric layer 8. An iridium oxide lower electrode 12 is provided on the silicon oxide layer 4, and SrTiO is provided on the lower electrode 12 of iridium oxide.₃, (Sr, Ba) TiO₃A high dielectric constant thin film having the perovskite structure of the above was formed as the dielectric layer 90. In this case as well, the dielectric property was improved as in the case of the ferroelectric substance. That is, it has been clarified that what has been described about the ferroelectric layer can be applied to the dielectric layer having a high dielectric constant.

FIG. 22 shows the structure of a ferroelectric capacitor according to another embodiment of the present invention. A silicon oxide layer 4, a lower electrode 12, a ferroelectric film (ferroelectric layer) 8, and an upper electrode 15 are provided on the silicon substrate 2. The lower electrode 12 is formed by an iridium layer 11 and an iridium oxide layer 13 formed on the iridium layer 11. Further, the upper electrode 15 is formed by an iridium layer 7 and an iridium oxide layer 9 formed on the iridium layer 7.

An enlarged view of the vicinity of the lower electrode 12 is shown in FIG. 23. Since the iridium layer 11 is a columnar crystal, it permeates oxygen in the ferroelectric film 8. In this example, the iridium oxide layer 13 is formed on the upper surface of the iridium layer 11. As described above, the iridium oxide layer 13 can prevent oxygen deficiency in the ferroelectric film 8. The same applies to the upper electrode 15.

In the above embodiment, since the iridium oxide layer is formed on both the lower electrode 12 and the upper electrode 15, a ferroelectric capacitor having excellent characteristics with little aging can be obtained. Even if either the lower electrode 12 or the upper electrode 15 has the above structure, some effect can be obtained. This point will also be described later.

FIG. 24 shows the manufacturing process of this ferroelectric capacitor. The surface of the silicon substrate 2 is thermally oxidized to form the silicon oxide layer 4 (FIG. 24A). Here, the thickness of the silicon oxide layer 4 is set to 600 nm. Next, using iridium as a target, the iridium layer 11 is formed on the silicon oxide layer 4 (FIG. 24B). Then O₂Heat treatment is performed at 800 degrees for 1 minute in the atmosphere to form the iridium oxide layer 13 on the surface of the iridium layer 11. The iridium layer 11 and the iridium oxide layer 13 are used as the lower electrode 12. Here, the lower electrode was formed to a thickness of 200 nm.

Next, a PZT film is formed as the ferroelectric layer 8 on the lower electrode 12 by the sol-gel method (FIG. 24C). Pb (CH) as a starting material₃COO)₂ 3H₂O, Zr (t-OC)₄H₉)₄, Ti (i-OC)₃H₇)₄The mixed solution of was used. After spin-coating this mixed solution, it was dried at 150 degrees Celsius (Celsius, the same applies hereinafter), and pre-baked at 400 degrees for 30 seconds in a dry air atmosphere. After repeating this 5 times, O₂Heat treatment of 700 degrees or more was performed in the atmosphere. In this way, the 250 nm ferroelectric layer 8 was formed. In addition, here, PbZr_XTi_1-XO₃In, x is 0.52 (hereinafter referred to as PZT (52, 48)) to form a PZT film.

Further, the iridium layer 7 is formed on the ferroelectric layer 8 by sputtering. Then O₂Heat treatment is performed at 800 degrees for 1 minute in the atmosphere to form the iridium oxide layer 9 on the surface of the iridium layer 7 (Fig. 24D). The iridium layer 7 and the iridium oxide layer 9 are used as the upper electrode 15. Here, the upper electrode 15 was formed to a thickness of 200 nm. In this way, a ferroelectric capacitor can be obtained.

25 and 26 show the fatigue characteristics of the remanent polarization Pr of the ferroelectric capacitor thus obtained. The measurement of this graph was performed by the same method as in FIGS. 5 and 6.

The vertical axis of FIGS. 25 and 26 represents the value of Pr / Po when the initial residual polarization is Po and the residual polarization after fatigue is Pr. The horizontal axis represents how many cycles the voltage of FIG. 7 was repeatedly applied. In the figure, the curve α is a case where only the lower electrode 12 is manufactured as in the above embodiment. Here, the silicon oxide layer 4 is 600 nm, the lower electrode 12 (oxidized surface of the iridium layer 11) is 200 nm, the ferroelectric film 8 (PZT (52/48)) is 250 nm, and the upper electrode is platinum. Consists of. The curve β is the case where the surface of the iridium layer of the lower electrode 12 is not oxidized (other conditions are the same as the curve α). Further, the curve γ is a case where the lower electrode 12 is formed of platinum (other conditions are the same as the curve α).

As is clear from this figure, when the surface of the iridium layer 11 is oxidized to form the iridium oxide layer 13, the deterioration of the remanent polarization Pr is considerably improved. The reason why iridium (when not oxidized) (curve β) is superior to platinum (curve γ) is that iridium is oxidized in other steps without special oxidation treatment. Is considered to be.

In this embodiment as well, it is preferable to provide the bonding layer 30 as described with reference to FIG.

Further, the embodiment of oxidizing the surface of iridium described here can be applied not only to a ferroelectric film but also to the above-mentioned dielectric film having a high dielectric constant, and the same effect can be obtained.

As described above, the escape of oxygen from the ferroelectric film can be prevented by oxidizing the surface of the iridium layer, but iridium oxide is formed on the surface and the orientation of the ferroelectric film deteriorates. As already described, this can be solved by providing an iridium layer, a platinum layer, an alloy layer of these, and the like on the iridium oxide layer 13 (see FIG. 10). However, it can also be solved by forming the lower electrode as follows.

First, as shown in FIG. 27, a platinum layer 80 (thin film conductor) is provided very thinly on the iridium layer 11. Here, it is set to 30 nm. Next, heat treatment is performed in this state. The platinum layer 80 on the surface does not react with oxygen and is not oxidized. Further, since the platinum layer 80 is formed thinly, the space between the crystals of the iridium layer 11 under the platinum layer 80 is oxidized, and iridium oxide is formed to prevent the permeation of oxygen. Therefore, it is possible to form the lower electrode 12 that can prevent the permeation of oxygen while the surface remains excellent in orientation. As the thin film conductor, any conductor may be used as long as it has good orientation and is hard to oxidize.

The iridium layer 11 oxidized after forming such a thin-film platinum layer 80 can be used alone as the lower electrode 12. However, in the example (see FIG. 10) in which a conductive layer with good orientation (iridium layer, platinum layer, etc.) is provided on the iridium oxide layer formed by sputtering to improve the orientation, the conductive layer with good orientation is provided. Can also be used as.

In FIG. 28B, the ferroelectric substance 8 is obtained by providing an iridium layer (200 nm) and a platinum layer (30 nm) having the structure of FIG. 27 on the iridium oxide (50 nm) and performing oxidation treatment as the lower electrode 12. Shows hysteresis characteristics. Further, FIG. 28A shows the hysteresis characteristics of the ferroelectric substance 8 when an iridium layer (200 nm) is provided on the iridium oxide layer (50 nm) and subjected to an oxidation treatment. As is clear from the figure, the hysteresis characteristic is superior when the structure shown in FIG. 27 is used.

Further, the examples described here can be applied not only to the ferroelectric film but also to the above-mentioned dielectric film having a high dielectric constant, and the same effect can be obtained.

<figref num="1">It is a figure which shows the composition of the ferroelectric capacitor according to one Example of this invention.</figref><figref num="2">It is a figure which shows the physical property of platinum and iridium.</figref><figref num="3">It is a figure which shows the non-volatile memory using the ferroelectric capacitor 22.</figref><figref num="4">It is a figure which shows the manufacturing process of a ferroelectric capacitor.</figref><figref num="5">It is a graph which shows the secular change of the residual polarization when the electrode material is changed.</figref><figref num="6">It is a graph which shows the secular change of the residual polarization when the electrode material is changed.</figref><figref num="7">It is a figure which shows the voltage applied at the time of performing a fatigue test.</figref><figref num="8">It is a figure which shows the structure for a fatigue test.</figref><figref num="9">It is a graph which shows the result of having verified that iridium oxide is not affected by the underlayer.</figref><figref num="10">It is a graph which shows the change of the remanent polarization Pr when platinum is provided on iridium oxide.</figref><figref num="11">It is a figure which shows the change of the remanent polarization Pr and the coercive electric field Ec when the mixing ratio of the alloy of platinum and iridium is changed.</figref><figref num="12">It is a graph which compares the case where the iridium oxide layer is provided on both the lower electrode and the upper electrode, and the case where it is provided only on the lower electrode.</figref><figref num="13">It is a graph which compares the case where the iridium oxide layer is provided on both the lower electrode and the upper electrode, and the case where it is provided only on the lower electrode.</figref><figref num="14">It is a graph which shows the temporal change of the current which occurs when a voltage is applied to a ferroelectric substance.</figref><figref num="15">In the graph of FIG. 14, it is a figure which shows the application direction of a voltage.</figref><figref num="16">It is a graph which shows the state which the characteristic of FIG. 14 changed by the imprint characteristic.</figref><figref num="17">It is a graph which shows the imprint characteristic.</figref><figref num="18">It is a graph which shows the imprint characteristic.</figref><figref num="19">It is a figure for demonstrating the cause of the difference in imprint characteristics.</figref><figref num="20">It is a figure which shows the Example which provided the bonding layer 30.</figref><figref num="21">It is a figure which shows the Example when the dielectric 90 which has a high dielectric constant is used.</figref><figref num="22">It is a figure which shows the structure of the ferroelectric capacitor by another Example.</figref><figref num="23">It is a figure which shows the mechanism which the iridium oxide layer prevents the escape of oxygen.</figref><figref num="24">It is a figure which shows the manufacturing process of the ferroelectric capacitor of FIG.</figref><figref num="25">It is a figure which compares and shows the secular change of the remanent polarization.</figref><figref num="26">It is a figure which compares and shows the secular change of the remanent polarization.</figref><figref num="27">It is a figure which shows the Example which oxidizes by providing the thin film platinum on the surface of iridium.</figref><figref num="28">It is a graph which compares and shows the effect when the electrode of FIG. 27 is used.</figref><figref num="29">It is a figure which shows the structure of the conventional ferroelectric capacitor.</figref><figref num="30">It is a figure which shows the state which oxygen escapes from the lower electrode 6 by platinum.</figref>

Code description

2 Silicon substrate 4 Silicon oxide layer 8 Ferroelectric layer 12 Lower electrode 15 Upper electrode 90 Dielectric layer with high dielectric constant