A multilayered thermistor structure

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(12) Patent Specification (10) SE 533 944 C2

Sweden (21) Patent application number: 0850160-3 (45) Patent granted: 2011-03-08 (41) Application generally available: 2010-06-20 (22) Patent application submitted: 12/12/2008 (24) Maturity date: 2008- 12-19 (83) Deposit of microorganism: - (30) Priority information: - (51) International class:

H01L 31/0352 (2006.01)

H01L 31/032 (2006.01)

G01J 5/20 (2006.01)

G01K7 / 22 (2006.01)

H01L 27/146 (2006.01)

H01L 31/09 (2006.01) (73) Patent holder: Henry H Radamson, Sätunavägen 1 IB, 195 46 Märsta SE

<td>(72) Inventor:</td><td>Henry H Radamson, Märsta SE</td>

<td>(74) Agents:</td><td>BRANN AB, Box 12246, 102 26 Stockholm SE</td>

<td>(54) Name:</td><td>A multi-layered structure</td>

<td>(56) Quoted publications:</td><td>EP 0812023 Al · EP 1912259 Al · SGE Wissmar SiGe quantum wells for uncooled long wavelength infra-red radiation (LWIR) sensors are included in J. Phys .: Conf. Looks. 100 042029, published online: 27 March 2008</td>

(47) Summary:

A thermistor structure according to the invention comprises a multi-layer structure having at least one quantum layer surrounded by barrier layers in a multi-layer structure. The quantum layer comprises Ge and can be in the form of either a quantum well or quantum dots. The barrier layer is a cold-doped Si layer, and the invention is intended to provide a means of compensating for the mechanical elongation in a multi-layer IR detector structure by cold-doping the quantum layer and barrier layer.

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Summary

A terrestrial structure according to the invention comprises a multi-layer structure having at least one quantum layer surrounded by barrier layers in a multi-layer structure. The quantum layer comprises Ge and can be in the form of either a quantum well or quantum dots. The barrier layer is a cold-doped Si layer, and the invention is intended to provide a means of compensating for the mechanical elongation in a multi-layer IR detector structure by cold-doping the quantum layer and barrier layer.

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A multi-layered structure

Technical area

The present invention relates to detector structures, and in particular detector structures for the infrared (IR) and terahertz regions.

The prior art

The infrared (IR) radiation region of the electromagnetic spectrum covers radiation of wavelengths between that of visible light and microwaves (750 nm and 1 mm, respectively). Radiation detection in the IR area has many applications in both civil and military purposes.

Infrared detection methods are divided into the two categories of photonic and thermal operating principles. The difference between these methods stems from their physical processes and this entails different areas of application. Photonic detectors have fast response times, on the order of 10 '⁵ s, and acts by excitation of charge carriers via IR absorption. The excitation of the charge carrier gives an electrical signal, which can be read at the output. Although the fast response time of photonic detectors makes them attractive, they must be cooled to low temperatures to reduce the noise and get a useful signal. This makes them profitable exclusively for high-cost / high-performance applications, where the cost of the detector is of secondary importance.

However, thermal detectors follow the principle where the electrical conductivity of a sensor is altered by heat generated via IR absorption in a thermistor structure. Thermal detectors have a response time of the order of 10³ s, and cannot compete with photonic speed devices. On the other hand, they are inexpensive to manufacture, and they do not need to be cooled to low temperatures to work properly. Thermal detectors can be a multi-layer structure of

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SiGe / Si with a performance that is highly dependent on the individual layer thicknesses.

A bolometer-shaped structure, a device for measuring energy for incident electromagnetic radiation that is particularly accurate in the high λ of the IR spectrum, is commonly used in the use of thermistor material. The bolometer is produced by processing e.g. multilayer structures to form individual free-standing pixels. Typical thermistor materials are vanadium oxide and one or more layers of (amorphous, polycrystalline or single crystalline) silicon or composite silicon-germanium based structures.

Disclosure of the Invention

The object of the present invention is to overcome at least some of the disadvantages of the prior art. This is achieved by the devices and methods specified in the independent claims.

A thermistor structure according to the invention comprises a multi-layer structure having at least one quantum layer surrounded by barrier layers in a multi-layer structure. The quantum layer comprises Ge and can be in the form of either a quantum well or quantum dots. The barrier layer is a cold-doped Si layer, and the invention is intended to provide a means of compensating for the mechanical elongation of a multi-layer IR detector structure by cold-dipping the quantum layer and barrier layer.

The invention is further related to increasing sensitivity in a multi-layer IR detector structure, and in particular to increasing the signal-to-noise ratio in a multi-layer IR detector structure.

Embodiments of the invention are defined in the dependent claims. Other objects, advantages and novel features of the invention will become apparent from the following detailed description of examples of embodiments.

533 944 of the invention when considered in conjunction with the accompanying drawings and claims.

Figure Description

Preferred embodiments of the invention will now be described with reference to the accompanying drawings, wherein

FIG. 1 shows the mechanical elongation distribution in a multi-layer structure with table-top contacts and barrier layers of Si_yC_y and quantum well layers of Sii_X Give_x.

FIG. 2 shows the mechanical elongation distribution in a multi-layer structure with table-top contacts and barrier layers of Si_yC_y and quantum well layers of Ge quantum dots.

FIG. 3 shows the mechanical elongation distribution in a multi-layer structure comprising a silicon bearing to prevent auto-doping from the table-raised contact layer.

FIG. 4 schematically shows bandgap structures for a) Si / SiGe and b) Sii_yC_y / Integration Interface_X Give_x.

FIG. 5 shows how the Temperature Coefficient of Resistance (TCR) depends on the Ge content of Si.

FIG. 6 shows a thermistor and shows absorption for different wavelengths and the absorption reaches its peak at λ / 4.

Detailed description of embodiments

The present invention relates to a multi-layer structure for use as a thermal detector in the IR or Terahertz region.

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According to the present invention (see Figs. 1, 2 and 3), a thermistor structure comprises at least one set of alternating layers, with a first layer of A 60 comprising Si and a second layer of B 50 comprising Ge, for use as a barrier layer and a quantum layer, respectively. , wherein said layers form a multi-layer structure with a sequence

A: B: Δ: A there

Δ = nx (A: B); n> 0 where the first layer is a Si_y C_y layer with a composition of 0.005 <y <0.035. The formula above means that the sequence can be repeated a desired number of times and where the quantum layer is always squeezed between barrier layers, ie. it always has barrier layers on both sides. In the formula above, n represents the number of times the sequence (A: B) of the multi-layer structure is repeated, and n can be any positive integer or zero. The multi-layer structure is formed on a substrate 10, from which it can be released later in the process. The substrate 10 may be Si, Ge, Al2O3, or any other material suitable for epitaxial growth.

The Ge-containing layer may be in the form of Ge quantum dots arranged between two barrier layer surfaces, or in the form of a SiGe quantum well layer arranged between two barrier layer surfaces, or in the form of a cold-doped SiGe quantum well layer or quantum dots arranged between two barrier layer surfaces. A very important parameter to control in such bearings is the mechanical elongation. In particular, in silicon-germanium (quantum well) on silicon (barrier) in multi-layer structures, a high germanium content is desired to induce a large mechanical elongation in a silicon-germanium arrangement of the atoms. The mechanical elongation is a consequence of

533 944 substitutively incorporated Ge atoms into the Si lattice. This mechanical elongation modifies the bandgap diagram resulting in an increased valence band shift in silicon germanium as shown in FIG. 4. Another effect of Ge incorporated into the Si lattice is also shown in FIG. 4, is band splitting between the heavy-hole (HH) and light-hole (LH) bands caused by the induced mechanical elongation. The increased band shift of the silicon metal layer in a SiGe / Si multi-layer structure is necessary to achieve high values ​​for the Temperature Coefficient of Resistance (TOR). The TCR value is a measure of the sensitivity of the structure, and a high TCR value means that the response from the structure is relatively strong, thus detecting incoming signals of relatively low intensity. In FIG. 5 shows how the concentration of Ge affects TCR in SiGe. In the region shown in the figure, between 20 atom percent and 45 percent atom of Ge, TCR increases linearly with Ge content.

However, although the mechanical elongation locally increases the efficiency of the structure as the TCR value is increased, the total mechanical elongation in the multi-layer structure gives rise to an increased noise level and thus reduces the efficiency of the structure. This type of detector noise is related to Johnson, generation / recombination and 1 / f noise. In the detector structure, Johnson noise is obtained from noise bandwidth and from the total resistance across the structure. Johnson noise does not depend on the applied voltage or current, which is the case for 1 / f noise and generation / recombination noise. For the latter type of noise, the generation rate usually decreases as activation energy increases. The main source of 1 / f noise is defects and interface irregularities due to relaxation of the mechanical elongation. A high quality epitaxial layer is a key issue for low noise in detectors. The present invention provides a method of elongating the structure by introducing carbon doping into the Si barrier layer. By mixing small ones

533 944 amounts of carbon in the silicon lattice, between 0.5% - 3.6%, the mechanical elongation in the Si barrier layer can be controlled to counteract the mechanical elongation in SiGe quantum well beats, which consequently results in a globally relaxed multi-layer structure. The amount of carbon in the barrier layer can compensate 10 times the amount of Ge in the quantum well layer. Thus, a concentration of approximately 30% to 35% of Ge in the quantum well layer can be compensated by cold doping of the barrier layer. This allows the formation of a thermistor quant well structure with a high band shift and thus a high TCR coefficient, while at the same time providing a relaxed structure where the mechanical elongation in the SiGe layer is neutralized by the counteracting mechanical elongation in the cold-doped Si barrier layer, which results in a high-efficiency thermistor which has a low noise level and therefore a high sensitivity and a high signal-to-noise ratio.

FIG. 1, 2 and 3 show multilayer structures which are elongation compensated as proposed by the present invention. The stretch diagram on the left side of the figures shows the stretch distribution throughout the structure, and how it is compensated for layer by layer, resulting in a globally relaxed structure.

In another embodiment of the present invention, SiGe comprises the quantum well layer Sn, with a composition Si_X._z Give_x Sn_z where 0.20 &lt;x &lt;1.00, and 0 &lt;z &lt;0.2. Introducing tin into the SiGe quantum well layer further increases the elongation, thus further increasing the TCR value. Due to proper relaxation in the multi-layer structure with the use of the cold-doped Si barrier layer, the result is a thermistor that exhibits even higher sensitivity, while maintaining the low noise level due to the globally relaxed multi-layer structure.

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In another embodiment of the present invention, the composition of the thermistor structure is given by Si i._x._z Give_x Sn_z where 0.50 &lt;x &lt;0.80, and 0 &lt;z &lt;0.2.

In another embodiment of the present invention, Si_xz Give_x Sn_z layers comprising in the thermistor structure doped with carbon. Choline incorporation in the quantum well stock, at a concentration of 1x10¹⁶ - 10x10²¹ cm³, preferably at a concentration of 10x10¹⁷ - 10x10²¹ cm³, even more preferably at a concentration of 1x10¹⁸-1x10²¹ cm³ , but most preferably at a concentration of 1x10²⁰ - 10x10²¹ cm³, greatly increases the thermal stability of the bearing. Thus, a cold-doped Sii_x._z Give_xSn_z in a Sii-_X._z Give_x Sn_z / Sii-_yC_y multi-layer structure to exhibit a high TCR value, be globally relaxed in terms of elongation, and be thermally stable up to high temperatures.

In another embodiment of the present invention, Si_x-_z Give_x Sn_z layer and Sii-γ C_y stored monocrystalline layers. This means that the layers do not have grain boundaries because the whole layer is a single grain. It is often desirable to have monocrystalline materials in many physical and especially in electronic applications, since the grain boundaries can play a significant and sometimes unpredictable role in the final performance of the application.

Another element that induces tensile elongation in silicon is boron. The small size of boron atoms compared to silicon atoms causes a contraction in the silicon matrix when boron is substitutionally incorporated. This contraction in the silicon contact can be used to further compensate for the elongation in a multi-layer structure. Thus, both the barrier layers in the multi-layer structure and the contacts surrounding the multi-layer structure can be used to compensate for the induced voltage in the doped SiGe quantum well layer. In general, a certain

533 944 concentration of carbon in the Si barrier layer capable of compensating for the elongation of ten times the concentration of Ge in the Si quantum well layer. Thus, the proportion of Ge relative to C in a Si lattice [1] should be of the order of 1:10. This means that a Si 0, 98 C 0.02 layer induces an elongation that substantially counteracts the elongation induced by a Si 0.8 Ge 0.2 layer. Recent reports have demonstrated that high quality Si i-_y C _y layers with carbon concentrations up to γ ​​= 0.036 can be grown [2j. This means that the induced elongation of up to 30% -35% Ge in the quantum well layer can be compensated for by cold doping of the barrier layer. The use of strain compensated Sii_X-_Z Give_x Sn_z / Sii_y C_y layers as thermistor material allow the growth of several layers with low defect density. However, if the quantum well layer is doped with Ge up to a level exceeding the limit of about 35% which can be compensated for by cold-doped barrier layers, then the silicon contact layers can be doped with boron to compensate for the amount of Ge in the quantum well layer which exceeds 35%, thus in a globally relaxed thermistor structure.

In one embodiment of the present invention, a first layer of table top Si covers a first side of the multi-layer structure, and a second layer of table top Si covers a second side of the multi-layer structure. This is shown in FIG. 1, 2 and 3. Boron concentration in the Si layer is> 1x10¹⁸ cm³, preferably the boron concentration is 1 x 10¹⁹ CRRR³ and most preferably, boron concentration is> 10x10²⁰ · cm³ and <1x10²¹ cm³. The more boron incorporated into the Si lattice, the higher the conductivity of Si, up to a concentration of> lx10²¹ cm³ which is the level where no more boron can be substitutively accepted by Si. The high conductivity of the table-mounted Si contact layer is needed for the contact layer to exhibit ohmic contact behavior. Table-top silicon bearings are integrated into many device structures such as ohmic small (thin) contact layers. A design comprising high table top Si can

533 944 is thus used as both a contact and an elongation compensated bearing for a Si_X-_Z Give_x Sn_z / Sii-_y C_y multilayer structure. An important integration aspect of such high-rise silica layers is to avoid auto-doping or thermal diffusion of boron atoms during epitaxial growth of Si_X._z Give_x Sn_z / S ii ~_y C_y multilayer structures.

In one embodiment of the present invention shown in FIG. 2, the second layer is a Quantum dot layer with composition Si_X._z Give_xSn_z where x = 1 and z = 0, placed between two layers of said Si i-_y C _ybarrier layers, wherein a sequence of Si_y C_y / Give quantum dots / Sii-_y C_y layers are a period of a multi-layer structure, which period is repeatable a desired number of times. The quantum dots in the quantum dot layer are distributed between two barrier layers in an ordered matrix pattern. The quantum dots are shifted relative to one another from one layer to another, to avoid the occurrence of nodules in the final multilayer structure.

It is also seen in all the figures which show a multi-layer structure according to the invention, FIG. 1, 2 and 3 and 6, that the thickness of the top and bottom Si_y C_y the layers are substantially the same thickness as the intermediate Si_y C_y layers.

In another embodiment of the present invention, the quantum dot layer comprises Si and / or Sn in addition to Ge, thus having a composition where x <1 and / or z> 0 is placed between two layers of said Si_y C_y barrier layers, where a sequence of Si_y C_y / SiGe or GeSn or SiGeSn quantum dots / Sii-_y C_y layers are a period of a multi-layer structure, which period is repeatable by a desired number of times. Si can be incorporated into Ge during deposition, or by diffusion from surrounding layers.

For the growth of Ge quantum dots on Si surface, the plant temperature becomes very important as a diffusion of Si atoms into the quantum dots can

533 944 occur. This diffusion of Si atoms results in an admixture, which reduces the strain energy in the system. As a result, the plant dynamics for dots are modified causing a larger dot size. This incorporation of Si into Ge in an uncontrolled manner can result in Ge or SiGe alloys with high defect density due to the strain relaxation. Quantum dots with these defects cannot be implemented in sensor structures because they generate high noise levels. It has been found that application of a low plant temperature or deposition of a very thin layer, about two monolayers, of carbon to the barrier layer before the growth of quantum dots attenuates the diffusion of Si into Ge. However, Si_y C_y the barrier layer of the invention is responsible for providing carbon to the interface between said barrier layer and quantum well layers, Ge or SiGe alloys, whereby the diffusion of Si into the quantum dots can be effectively substantially reduced. The new design then consists of cold dipped Ge dots / Sii-_y C_ymultilayer structures.

The quantum dots 55 can have a diameter in a range of 50 to 150 nm, preferably in a range of 70 to 130 nm, and most preferably in a range of 90-110 nm. Furthermore, the quantum dots can have a height in a range of 4-12 nm, preferably a height in a range of 5-10 nm, and most preferably a height in a range of 5-8 nm.

In one embodiment of the present invention, the multi-layer structure comprising quantum dots is contacted on a first side and a second side of a table-top Si layer which covers both ends of the structure shown in FIG. 2. The boron concentration in the table-mounted Si layer is> 1x10¹⁸ cm ³, preferably the boron concentration is> 1x10¹⁹ cm³ and most preferably, the boron concentration is> 1x10²⁰ cm ³ and <1x10²¹ * cm³

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Referring to FIG. 3, in the case that the contact material is table-mounted silicon, the boron atoms in the table-mounted silicon contact layer 100 may diffuse under high temperature conditions, or auto-doping may occur during epitaxial growth and incorporate even into adjacent layers. This will greatly impair the performance of the thermistor structure. Thus, in one embodiment of the present invention shown in FIG. 3, a silicon layer 200 is disposed between the table-mounted silicon contact layer 100 and the first barrier layer 60. This silicon layer 200 effectively prevents auto-doping or thermal diffusion of boron into the thermistor structure. This method of preventing auto-doping can be applied to the contacts on both sides of the structure, and in all cases when table-doped silicon contact layer 100 is used in a thermistor structure.

Fig. 6 shows a complete thermistor structure containing absorption layers as a function of different wavelengths. The thermistor comprises a multi-layer structure and a reflector 120, that is, a reflective mirror. Each barrier layer 60 containing carbon is spaced a quarter of a wavelength from the reflector 120 to maximize the absorption intensity for each desired wavelength to detect. Thus, the thermistor structure can be optimized for absorption of multiple wavelengths, depending on the number of layers in the multi-layer structure. This means that in FIG. 6, λ corresponds to 1/4 corresponds to di, λ2 / 4 corresponds to d2, λ3 / 4 corresponds to d3 and λ₄ / 4 corresponds to d₄. The illustration in the figure comprises 4 distances corresponding to four different wavelengths. However, this is for illustrative purposes only, and not intended as a limitation and a thermistor structure can be optimized to receive more as well as fewer different wavelengths.

In another embodiment of the present invention, a method of manufacturing a thermistor structure comprising at least one set of alternating layers, a first layer A having a composition Si_y and a second layer B having a composition Si 1._x._z Give_x Sn_z> in order to

533 944 is used as a respective barrier and quantum layer, said layer in the multilayer structure in the form of the sequence

A: B: Δ: A there

Δ = nx (A: B), n> 0 and

0.20 &lt;x &lt;, 1.00

0.005 &lt;y &lt;0.035

0 &lt;z &lt;0th 2 comprising the steps of;

- providing a substrate

- placing substrate in a deposition chamber

- pump out of the deposition chamber to a pressure &lt;10-¹⁰ Dry

- introducing gases for deposition through gas inlet into the vacuum chamber

- deposit the desired number of layers according to A: B: Δ: A using a deposition method

- Flush the chamber

- Ventilate the chamber

The method may also include steps for heating the substrate.

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While the invention has been described in connection with what is currently considered the most practical and advantageous embodiments, it is to be understood that the invention is not to be limited to the embodiments shown. On the contrary, it is intended to cover various modifications and equivalent devices within the scope of the appended claims.

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References [1] CW Liu, YD Tseng, and YS Huang, Applied Physics Letters, vol 75 (1999) 2271.

[2] Mathias Bauer, Vladimir Machkaoutsan, and Chantal Arena,

Semicond. Sci. Technol. 22 (2006) 183.

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