JP2008082790A - Infrared sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an infrared sensor capable of achieving higher sensitivity than before. <P>SOLUTION: On the side of one surface of a base substrate 10 having a cavity 15 for thermal insulation, an infrared light reception part 30 arranged inside an inner circumferential line 15a of the cavity 15 in a plan view is supported at the base substrate 10 via two beam parts 20 formed along the one surface. The beam parts 20 are made of a thermoelectric material, a type of a thermo-sensitive material, and each beam part 20 has one end part 21 layered on a peripheral part of the cavity 15 on the side of the one surface and connected to the base substrate 10 and the other end part 22 constituting part of the infrared light reception part 30. The infrared light reception part 30 is provided with an infrared absorbing part 40 made of only gold black, an infrared absorbing material which absorbs infrared radiation. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a thermal-type infrared sensor formed using a micromachining technique or the like.

  Conventionally, as an infrared sensor of this type, an infrared light receiving unit positioned on the inner surface of a cavity in a plan view on one surface side of a base substrate having a thermal insulation cavity is formed through a plurality of beam portions. The infrared light receiving part is supported by the base part supported by the base substrate via a plurality of beam parts, the temperature detection part formed on the base part, and the side opposite to the base part side in the temperature detection part An infrared sensor composed of an infrared absorbing portion formed in the above has been proposed (see, for example, Patent Documents 1 and 2).

  By the way, the infrared sensor disclosed in Patent Document 1 is an infrared image sensor in which infrared light receiving portions are arranged in a two-dimensional array in a plane parallel to the one surface of the base substrate. By making the cross-sectional shape of each beam part an arched shape, the total length of each beam part can be reduced without changing the aperture ratio of each pixel (cell) (the ratio of the area of the infrared light receiving part to the area of the pixel size). The length is reduced to reduce the thermal conductance of each beam. Here, in the infrared sensor disclosed in Patent Document 1, a base substrate is formed using a silicon substrate, and the base portion and each beam portion are formed of a dielectric film such as a silicon nitride film or a silicon oxide film. And an example constituted by a laminated film of a polycrystalline silicon film and a dielectric film made of a silicon oxide film is disclosed.

  In addition, the infrared sensor disclosed in Patent Document 1 includes an n-type semiconductor element composed of an n-type polycrystalline silicon layer provided on one of the beam portions adjacent to each other in the outer peripheral direction of the base portion, and the other beam portion. A p-type semiconductor element made of a p-type polycrystalline silicon layer provided on the base is connected via a junction made of a metal material (for example, aluminum) on the base portion, and an n-type semiconductor element and a p-type semiconductor The hot junction part which consists of each one end part of an element and a junction part comprises the temperature detection part.

  In addition, the infrared sensor disclosed in the above-mentioned patent document 2 absorbs infrared rays by forming a high thermal conductive layer between the infrared absorbing part and the temperature detecting part composed of the hot contact part in order to improve the response speed. The heat transfer rate from the temperature sensor to the temperature detector is improved. Here, in the infrared sensor disclosed in Patent Document 2, a base substrate is formed using a silicon substrate, the base portion is formed of a dielectric film made of a silicon nitride film, and the beam portion is a silicon nitride film. An example in which an n-type semiconductor element and a p-type semiconductor element are embedded in each beam portion is disclosed in which the first dielectric film is made of a laminated film of a second dielectric film made of a silicon oxide film. .

Note that Patent Documents 1 and 2 describe that the same technique can be applied to a resistance bolometer type infrared sensor as well as a thermopile type infrared sensor.
Japanese Patent Laid-Open No. 11-258039 Japanese Patent No. 3339276

  By the way, in the infrared sensor disclosed in the above-mentioned patent document 1, by making the cross-sectional shape of the beam part an arched shape, higher sensitivity can be achieved compared to the infrared sensor disclosed in the above-mentioned patent document 2, The beam forming process becomes complicated and the cost increases.

  Further, in the thermopile type infrared sensor disclosed in Patent Documents 1 and 2, each beam portion is composed of at least a dielectric film and a semiconductor element, and has high sensitivity due to the thermal conductance of the dielectric film. There was a problem that the conversion was limited. Similarly, in a resistance bolometer-type infrared sensor, each beam portion is composed of at least a dielectric film and a wiring, so that the high sensitivity is limited due to the thermal conductance of the dielectric film. was there. In the infrared sensors disclosed in Patent Documents 1 and 2, since the infrared light receiving unit includes a base unit that supports the temperature detection unit and the infrared absorption unit, the response speed is slow due to the heat capacity of the base unit. There was also a problem.

  This invention is made | formed in view of the said reason, The objective is to provide the infrared sensor which can attain high sensitivity compared with the past.

  According to a first aspect of the present invention, there is provided a plurality of beams in which an infrared light receiving portion positioned on the inner surface of a cavity in a plan view on one surface side of a base substrate having a thermal insulating cavity is formed along the one surface. An infrared sensor supported on a base substrate via a portion, wherein the beam portion is formed only of a heat sensitive material or a wiring material.

  According to the present invention, since the beam portion is formed only of the heat-sensitive material or the wiring material, the thermal conductance of the beam portion can be reduced as compared with the conventional case, and high sensitivity can be achieved.

  The invention of claim 2 is characterized in that, in the invention of claim 1, the beam portion is formed only of the heat-sensitive material, and the heat-sensitive material is a thermoelectric material.

  According to the present invention, since the thermoelectric material has a lower thermal conductivity than a general wiring material, the thermal conductance of the beam portion is reduced compared to the case where the beam portion is formed of only a general wiring material. It is possible to achieve high sensitivity.

  The invention of claim 3 is the invention of claim 2, wherein the base substrate is formed using a silicon substrate, and the thermoelectric material is polycrystalline silicon or single crystal silicon.

  According to the present invention, the compatibility with the silicon process is good, the thermal conductance can be easily reduced by thinning and miniaturizing the beam portion, the circuit can be easily integrated, and the beam portion can be easily integrated. The mechanical properties (mechanical properties) of the material can be made equal to the mechanical properties of the material of the base substrate, and damage to the beam portion due to environmental changes can be prevented.

  According to a fourth aspect of the present invention, in the first to third aspects of the invention, the infrared light receiving portion is formed of only a temperature detecting portion supported by the base substrate via the beam portion and an infrared absorbing material. It is characterized by comprising an infrared absorption part in contact with the detection part.

  According to this invention, the infrared light receiving part is configured by a temperature detection part supported by the base substrate via the beam part, and an infrared absorption part formed of only an infrared absorbing material and in contact with the temperature detection part. And since there is no base part for supporting a temperature detection part and an infrared absorption part, in the structure provided with the infrared absorption part, the heat capacity of the said infrared light-receiving part can be made small, and a response speed can be improved.

  The invention of claim 5 is characterized in that, in the invention of claim 4, the infrared absorbing material is a porous material.

  According to this invention, compared with the case where the infrared absorbing material is a non-porous material, the heat capacity of the infrared absorbing portion per unit volume can be reduced, and the response speed can be increased.

  The invention of claim 6 is characterized in that, in the invention of claim 4, the infrared absorbing material is a noble metal.

  According to the present invention, since the infrared absorbing portion is less susceptible to etching damage during the etching for forming the cavity during manufacturing, the manufacturing is facilitated.

  The invention according to claim 1 has an effect that the thermal conductance of the beam portion can be reduced as compared with the prior art, and high sensitivity can be achieved.

(Embodiment 1)
As shown in FIGS. 1A and 1B, the infrared sensor of the present embodiment has an inner side of an inner peripheral line 15a of the cavity 15 in a plan view on one surface side of the base substrate 10 having the cavity 15 for thermal insulation. The infrared light receiving portion 30 located at the base plate 10 is supported by the base substrate 10 via a plurality of (two in this embodiment) beam portions 20 formed along the one surface.

  The base substrate 10 is formed using a semiconductor substrate 10a made of a silicon substrate, and an insulating layer 11 is formed on one surface of the semiconductor substrate 10a. Here, the insulating layer 11 is composed of a laminated film of a silicon oxide film formed on the one surface of the semiconductor substrate 10a and a silicon nitride film formed on the silicon oxide film.

  By the way, the infrared sensor of this embodiment is a thermopile type infrared image sensor, and each beam part 20 is formed only with the thermoelectric material which is a kind of heat sensitive material. Specifically, one beam portion 20 (20a) is formed of n-type polycrystalline silicon, and the other beam portion 20 (20b) is formed of p-type polycrystalline silicon. In this embodiment, a silicon substrate is used as the semiconductor substrate 10a, and each beam portion 20 is formed of polycrystalline silicon. However, impurities are contained in a single crystal silicon layer on an insulating film in a so-called SOI (Silicon on Insulator) substrate. As a thermoelectric material, each beam portion 20 is formed, the insulating film of the SOI substrate constitutes the insulating layer 11, and the silicon substrate immediately below the insulating film in the SOI substrate constitutes the semiconductor substrate 10a. Good. In this case, not only the Seebeck coefficient of the thermoelectric material constituting each beam portion 20 is increased, but also the mechanical properties of the beam portion 20 and the mechanical properties of the semiconductor substrate 10a made of a single crystal silicon substrate are matched. There is an advantage that it becomes easy.

  Each beam portion 20 (20a), 20 (20b) has one end portion 21 (21a), 21 (21b) on the peripheral surface of the cavity 15 on the one surface side of the base substrate 1 (for example, Al, Al -Si, etc.) are connected to the metal wirings 13 (13a) and 13 (13b), and the other end portions 22 (22a) and 22 (22b) are overlapped with a part of the infrared absorbing portion 40 described later. A part of the infrared light receiving unit 30 is formed. In the present embodiment, the shape of the infrared light receiving unit 30 in plan view is a rectangular shape (here, a square shape), and each beam unit 20 has a substantially entire circumference of the outer peripheral edge of the infrared light receiving unit 30 with all the beam units 20. It is formed in a surrounding shape. Specifically, the planar view shape of each beam portion 20 is an L shape along two adjacent sides of the infrared light receiving portion 30.

The infrared light receiving unit 30 includes an infrared absorbing unit 40 formed only of an infrared absorbing material that absorbs infrared rays (in this embodiment, a noble metal such as gold black). Here, in the present embodiment, a noble metal (for example, gold black) is used as the infrared absorbing material, and the infrared absorbing portion 40 is composed of a beam portion 20a formed of n-type polycrystalline silicon and a p-type. It also serves as a joint for connecting the other end portions 22a and 22b to the beam portion 20b formed of polycrystalline silicon. The other end portions 22a and 22b and the infrared ray absorbing portion 40 of the beam portions 20a and 20b The constructed hot junction part constitutes a temperature detection part, and the joint part between the one end part 21a, 21b of each beam part 20a, 20b and the metal wiring 13a, 13b constitutes a cold junction part. Therefore, when adopting general SiON or Si ₃ N ₄ as the infrared absorbing material and providing the joint portion connecting the other end portions 22a, 22b of the beam portions 20a, 20b separately from the infrared absorbing portion 40. In comparison, the heat capacity can be reduced and the response speed can be increased. However, even in the case where the joint portion that connects the other end portions 22a and 22b of the beam portions 20a and 20b is provided separately from the infrared absorbing portion 40, as the infrared absorbing material of the infrared absorbing portion 40, for example, porous SiO ₂ (porous) If a porous material such as silica is employed, the heat capacity of the infrared absorbing portion 40 can be reduced as compared with the case where a non-porous material such as SiON or Si ₃ N ₄ is employed. The shape of the infrared light receiving unit 30 in plan view is the same as that of the infrared absorbing unit 40.

  Here, an example of the manufacturing method of the infrared sensor of this embodiment is demonstrated easily.

  First, an insulating film made of a silicon oxide film and a silicon nitride film is formed on the entire surface of the semiconductor substrate 10a made of a silicon substrate, and then a region corresponding to a region where the cavity 15 is to be formed in the insulating film. The silicon nitride film is removed by etching. Subsequently, a polycrystalline silicon layer serving as the basis of each beam portion 20 is formed on the entire surface of the one surface side of the semiconductor substrate 10a by a low pressure CVD method, and then a high temperature annealing process for removing residual stress at the time of film formation. (For example, the annealing temperature is 1150 ° C. and the annealing time is 2 hours). This high-temperature annealing treatment is extremely important as a treatment for reducing the residual stress in order to prevent deformation and breakage of the beam portion 20 due to residual stress in finally maintaining the structure of the beam portion 20 with polycrystalline silicon alone. . The high-temperature annealing process is also extremely important as a process for reducing the difference in linear expansion coefficient between the semiconductor substrate 10a made of a silicon substrate and the beam part 20 in order to prevent the beam part 20 from being changed or damaged due to environmental temperature changes. is there.

  After the above-described high-temperature annealing treatment, the polycrystalline silicon layer is patterned using photolithography technology and etching technology so that portions corresponding to the beam portions 20 (20a) and 20 (20b) remain, and then, A polycrystalline silicon layer corresponding to one beam portion 20a is doped with a p-type impurity by, for example, an ion implantation method, and an n-type impurity is doped into the polycrystalline silicon layer corresponding to the other beam portion 20b, for example, with an ion implantation method. Doping by such as.

  Thereafter, the entire surface on the one surface side of the semiconductor substrate 10a is made of a silicon oxide film for protecting the polycrystalline silicon layer corresponding to each of the beam portions 20a and 20b when etching for forming the cavity 15 is performed later. A surface protective layer is formed by a CVD method or the like. Subsequently, an opening for contact between the infrared absorbing portion 40 and the other end portion 22 of each beam portion 20 is formed using a photolithography technique and an etching technique, and then the entire surface on the one surface side of the semiconductor substrate 10a. In addition, a barrier layer (for example, a Ti layer) for preventing the contact portion between the infrared absorbing portion 40 and the other end portion 22 of each beam portion 20 from being damaged during etching to form the cavity 15 is provided. Then, a porous gold black layer serving as a basis for the infrared absorbing portion 40 is formed on the entire surface of the one surface side of the semiconductor substrate 10a by a gas evaporation method.

  Thereafter, the first resist layer formed by applying a high-viscosity photosensitive resist on the entire surface of the one surface side of the semiconductor substrate 10a is patterned so as to leave a region where the infrared absorption portion 40 is to be formed, and is subjected to ion milling or the like. After removing the unnecessary part of the gold black layer, the infrared absorption part 40 is formed, and then the first resist layer is removed with an organic solvent such as acetone.

  Thereafter, the second resist layer formed by applying a high-viscosity photosensitive resist on the entire surface of the one surface side of the semiconductor substrate 10a remains so as to leave a portion other than the region where the etching solution introduction hole for forming the cavity 15 is to be formed. Then, using the patterned second resist layer as a mask, an etchant introduction hole is formed in the silicon oxide film on the one surface side of the semiconductor substrate 10a, and the second resist layer is made of an organic material such as acetone. Remove with solvent.

  Thereafter, the cavity 15 is formed by anisotropically etching the semiconductor substrate 10a through the etching solution introduction hole using an alkaline solution such as a TMAH solution. Thereafter, an unnecessary silicon oxide film remaining around the beam portion 20 and an unnecessary silicon oxide film immediately below the infrared absorbing portion 40 may be removed by etching using an HF-based etching solution or the like.

  In the infrared sensor of the present embodiment described above, since the beam portion 20 is formed only from a thermoelectric material that is a kind of heat-sensitive material, the thermal conductance of the beam portion 20 can be reduced as compared with the conventional case, and the sensitivity is high. Can be realized. In addition, since the thermoelectric material has a lower thermal conductivity than a general wiring material (for example, Al, Al-Si, etc.), the beam portion is compared with a case where the beam portion 20 is formed only from a general wiring material. The thermal conductance of 20 can be reduced, and high sensitivity can be achieved.

  In the present embodiment, the base substrate 10 is formed using a semiconductor substrate 10a made of a silicon substrate, and the thermoelectric material is polycrystalline silicon or single crystal silicon. The thermal conductance can be easily reduced by thinning and miniaturization, and the integration of circuits (driving circuit, signal processing circuit, etc.) is facilitated, and the mechanical properties (mechanical properties) of the material of the beam portion 20 are reduced. Since the mechanical properties of the material of the base substrate 10 can be made equal, and damage to the beam portion 20 due to environmental changes (for example, temperature changes) can be prevented, the reliability becomes high. Further, in the present embodiment, since a noble metal is employed as the infrared absorbing material, the infrared absorbing portion 40 is not easily damaged during etching to form the cavity 15 at the time of manufacturing, which facilitates manufacturing.

(Embodiment 2)
The basic configuration of the infrared sensor of the present embodiment is substantially the same as that of the first embodiment. As shown in FIGS. 2A and 2B, the inside of the cavity 15 in the plan view on the one surface side of the base substrate 10 is shown. Two infrared light receiving portions 30 located inside the peripheral line 15a are provided, and each infrared light receiving portion 30 is supported by the base substrate 10 via two beam portions 20 (20a) and 20 (20b). Is different. In addition, the same code | symbol is attached | subjected to the component similar to Embodiment 1, and description is abbreviate | omitted.

  Further, in the present embodiment, the beam absorbing portion 20a made of p-type polycrystalline silicon, the beam portion 20b made of n-type polycrystalline silicon, and both the beam portions 20, 20b are interposed between the infrared absorbing portions having conductivity. Two thermocouples 40 are formed, and these two thermocouples are connected in series by a metal connection layer 14 formed on the periphery of the cavity 15 in the base substrate 10.

  Also in the infrared sensor of this embodiment described above, since the beam portion 20 is formed only of a thermoelectric material which is a kind of heat-sensitive material, similarly to the first embodiment, the thermal conductance of the beam portion 20 is increased compared to the conventional case. It can be made small and high sensitivity can be achieved.

(Embodiment 3)
The infrared sensor of the present embodiment is a thermistor type infrared sensor, and as shown in FIGS. 3A and 3B, each beam portion 20 is made of a wiring material (preferably, Ti having excellent chemical resistance). , W, Mo and other carbides and nitrides, noble metals such as Pt and Ir), and the infrared light receiving unit 30 is formed of a thermistor material (for example, amorphous silicon, titanium, vanadium oxide, etc.). 35 and an infrared absorbing portion 40 formed only of an infrared absorbing material (for example, a porous material such as porous silica). In addition, the same code | symbol is attached | subjected to the component similar to Embodiment 1, and description is abbreviate | omitted.

  The temperature detection unit 35 is formed in a meandering shape (in this embodiment, a folded shape), and both ends are electrically connected to the beam unit 20 formed only from the wiring material. It is connected.

  Thus, in the infrared sensor according to the present embodiment, since the beam portion 20 is formed only of the wiring material, the thermal conductance of the beam portion 20 can be reduced as compared with the conventional case, and high sensitivity can be achieved. In addition, the infrared light receiving unit 30 is formed of a thermistor material and is supported by the base substrate 10 via the beam portion 20, and the intermediate formed of only the infrared absorbing material and obstructs heat conduction to the temperature detecting unit 35. Infrared absorbing portion 40 that is in contact (ie, directly contacted) without a layer or the like, and there is no base portion for supporting temperature detecting portion 35 and infrared absorbing portion 40. In the configuration provided, the heat capacity of the infrared light receiving unit 30 can be reduced, and the response speed can be improved. Even in the configuration of the first embodiment, since there is no conventional base portion, the heat capacity of the infrared light receiving portion 30 can be reduced, and the response speed can be improved.

  Further, in the infrared sensor of the present embodiment, since the infrared absorbing material is a porous material, the heat capacity of the infrared absorbing unit 40 per unit volume can be reduced and the response speed can be increased as compared with the case of a non-porous material. Can be planned.

  In this embodiment, each beam portion 20 is formed of a wiring material. However, the beam portion 20 is not limited to the wiring material, and may be formed of a thermistor material that is a kind of heat sensitive material. 35 and each beam part 20 can be formed continuously and integrally, and there is an advantage that the manufacturing process can be simplified.

  By the way, the infrared sensor described in each embodiment is an infrared image sensor in which the infrared light receiving units 30 are arranged in a two-dimensional array. The infrared light receiving unit 30 is highly effective in increasing sensitivity and response speed. Of course, an infrared sensor having only one sensor may be used.

Embodiment 1 is shown, (a) is a schematic plan view, and (b) is a schematic cross-sectional view taken along line A-A ′ of (a). Embodiment 2 is shown, (a) is a schematic plan view, and (b) is a schematic cross-sectional view taken along line A-A ′ of (a). Embodiment 3 is shown, (a) is a schematic plan view, (b) is an A-A 'schematic cross-sectional view of (a).

Explanation of symbols

10 Base substrate 10a Semiconductor substrate (silicon substrate)
15 Cavity 15a Inner circumference line 20 Beam part 30 Infrared light receiving part 40 Infrared absorbing part

Claims (6)

  An infrared light receiving portion positioned on the inner surface of the cavity in a plan view on one surface side of the base substrate having a thermal insulating cavity is formed on the base substrate via a plurality of beams formed along the one surface. An infrared sensor supported, wherein the beam portion is formed only of a heat sensitive material or a wiring material.   The infrared sensor according to claim 1, wherein the beam portion is formed only of the heat-sensitive material, and the heat-sensitive material is a thermoelectric material.   3. The infrared sensor according to claim 2, wherein the base substrate is formed by using a silicon substrate, and the thermoelectric material is polycrystalline silicon or single crystal silicon.   The infrared light receiving unit includes a temperature detection unit supported by the base substrate through the beam unit, and an infrared absorption unit formed of only an infrared absorbing material and in contact with the temperature detection unit. The infrared sensor according to any one of claims 1 to 3.   The infrared sensor according to claim 4, wherein the infrared absorbing material is a porous material.   The infrared sensor according to claim 4, wherein the infrared absorbing material is a noble metal.

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