JP2010276516A - Infrared imaging element and manufacturing method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an infrared imaging element capable of securing reliability in electric insulation and responding at a high speed. <P>SOLUTION: A method for manufacturing a thermal infrared imaging element having a plurality of pixels arranged on an SOI substrate and a circuit on the SOI substrate for reading electric signals from the pixels, includes the steps of forming on the element a detecting section detecting a temperature by a silicon diode; forming the silicon diode on an SOI layer of the SOI substrate in the step of forming the detecting section; and coating the silicon diode with a thermally-oxidized film generated by thermally oxidizing a surface of silicon constituting the silicon diode, and an embedded oxidized film layer of the SOI substrate. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an uncooled infrared imaging device having sensitivity in the far infrared region.

  Conventional non-cooling type (or “thermal type”) infrared imaging devices can be miniaturized because they do not require a refrigerator, and in recent years, the price has been reduced for consumer applications. Yes. From such a background, research and development of an uncooled infrared imaging element using a silicon PN diode that can share a manufacturing process with a general-purpose LSI as a temperature detection unit has been actively conducted (for example, see Patent Document 1).

  Conventional uncooled infrared imaging devices are manufactured in the same manufacturing process by adding the manufacturing process of the temperature detection unit to the manufacturing process of the signal readout circuit unit that can be manufactured in the manufacturing process of the general-purpose LSI. In addition, a silicon oxide film is deposited between the metal wirings in order to ensure electrical insulation of the signal readout circuit unit. At the same time, a similar amount of silicon oxide film is deposited on the temperature detection unit. It was. Furthermore, since it is necessary to flatten the silicon oxide film in order to build a fine LSI structure, the silicon oxide film is deposited on the temperature detection part more than necessary to ensure electrical insulation. It was.

JP 2005-009998 A

  As described above, in the conventional technique, a considerable amount of silicon oxide film is deposited on the temperature detection unit manufactured in the same process as the signal readout unit, so that the heat capacity of the temperature detection unit increases more than necessary. Was. For this reason, the thermal time constant has increased, and it has been necessary to prevent an afterimage phenomenon when an object moving at high speed is imaged.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to obtain an infrared imaging device capable of high-speed response while ensuring reliability in electrical insulation.

  A manufacturing method of an infrared imaging device according to the present invention is a manufacturing method of a thermal type infrared imaging device having a plurality of pixels and a circuit for reading out an electric signal from the pixels on a main surface of an SOI substrate, and the pixel is made of silicon. Including a step of forming a detection portion for detecting temperature by a diode, and in the step of forming the detection portion, a silicon diode is formed on the SOI layer of the SOI substrate, and the surface of silicon constituting the silicon diode is further thermally oxidized to generate And a step of covering the silicon diode with the thermal oxide film and the buried oxide film layer of the SOI substrate.

  According to another aspect of the present invention, there is provided a thermal infrared imaging device having a plurality of pixels and a circuit for reading out electrical signals from the pixels on a main surface of the SOI substrate, wherein the pixels detect a temperature by a silicon diode; And a support that holds the detection unit away from the semiconductor substrate, and the silicon diode is formed by thermally oxidizing the buried oxide film layer of the SOI substrate and the surface of silicon constituting the silicon diode. It is also an infrared imaging device characterized by being covered with an oxide film.

  The infrared imaging device according to the present invention uses a thermal oxide film obtained by oxidizing the silicon of the silicon diode itself as a protective film for protecting the silicon diode. Therefore, a thin and dense thermal oxide film as a high-quality insulating film can be used, so that the protective film for protecting the silicon diode can be thinned, and the thermal capacity of the temperature detection unit can be reduced. In addition, since a thermal oxide film is used, it is possible to obtain an infrared imaging device capable of high-speed response while ensuring reliability in electrical insulation.

It is the perspective view which showed the structure of the infrared imaging element in Embodiment 1 of this invention. It is a top view of the infrared detector of the infrared imaging element in Embodiment 1 of this invention. It is sectional drawing of the infrared detector of the infrared imaging element in Embodiment 1 of this invention. It is sectional drawing of the temperature detection part in Embodiment 1 of this invention. It is sectional drawing in the manufacturing process of the temperature detection part in Embodiment 1 of this invention. It is sectional drawing in the manufacturing process of the temperature detection part in Embodiment 1 of this invention. It is sectional drawing in the manufacturing process of the temperature detection part in Embodiment 1 of this invention. It is sectional drawing in the manufacturing process of the temperature detection part in Embodiment 1 of this invention. It is sectional drawing in the manufacturing process of the temperature detection part in Embodiment 1 of this invention. It is sectional drawing in the manufacturing process of the temperature detection part in Embodiment 1 of this invention. It is sectional drawing in the manufacturing process of the temperature detection part in Embodiment 2 of this invention. It is sectional drawing in the manufacturing process of the temperature detection part in Embodiment 2 of this invention. It is sectional drawing in the manufacturing process of the temperature detection part in Embodiment 2 of this invention. It is sectional drawing in the manufacturing process of the temperature detection part in Embodiment 2 of this invention. It is sectional drawing in the manufacturing process of the temperature detection part in Embodiment 2 of this invention. It is sectional drawing in the manufacturing process of the infrared detector in Embodiment 2 of this invention.

Embodiment 1 FIG.
1 is a perspective view showing an outline of a configuration of an infrared imaging element according to Embodiment 1 of the present invention. FIG. 2 is an enlarged plan view of the infrared detector denoted by reference numeral 100 in FIG. 1. The infrared absorber 101 (broken line in FIG. 2) is seen through, and the support body 102 and the temperature detector 103 are separated. It is the top view shown typically. FIG. 3 is a cross-sectional view of the AA cross section shown in FIG. 2 as viewed in the direction of the arrow, and is a schematic view showing a cross section of the infrared detector 100. FIG. 4 is an enlarged view of the temperature detection unit 103 shown in FIG. 5 to 10 are schematic views of the cross section shown in FIG. 3 viewed in the order of the manufacturing process of the infrared imaging device.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In addition, what attached | subjected the same code | symbol is the same or it corresponds, This is common in the whole text of a specification.

First, the overall configuration of the infrared imaging element 303 will be described.
In FIG. 1, an infrared imaging element 303 includes a signal processing circuit 302 and a detector array 301 including a group of a plurality of infrared detectors 100 arranged in a row and column direction at a predetermined pitch. The output signal output from the infrared detector 100 is read by the signal processing circuit 302 and output to the outside of the element.

Next, the infrared detector 100 will be described with reference to FIGS.
The infrared imaging element of the present embodiment has a configuration in which a PN junction diode 105 manufactured on a buried oxide film layer 305 of an SOI (Silicon On Insulator) substrate 300 which is a silicon semiconductor substrate is a temperature detection unit 103. The PN junction diode 105 has a function of converting heat into an electrical signal. In addition, the substrate 300 under the buried oxide film layer 305 has a hollow portion 106 in which a cavity is partially formed by etching. Further, the temperature detection unit 103 is supported by being separated from the substrate 300 by the support body 102. Therefore, a structure that reduces heat conduction from the temperature detection unit 103 to the substrate 300 is possible. This structure is manufactured using a micromachining technique. Further, the support 102 is constituted by a laminate of a metal wiring layer 410 and a silicon oxide film. In this embodiment, the PN junction diode 105 is formed in an SOI layer that is a part of the SOI substrate 300.

The infrared detector 100 will be described in detail with reference to FIG.
The infrared detector 100 is roughly divided into an infrared absorption unit 101, a support body 102, and a temperature detection unit 103. The temperature detection unit 103 is mounted with two PN junction diode units 105 connected in series, and each PN junction diode is electrically coupled by a metal wiring layer 104. In FIG. 2, four PN junction diodes 105 are connected, but the number of connections can be increased.

First, the infrared detection principle of the infrared detector 100 will be described.
First, when infrared rays emitted from a subject to be imaged by the infrared imaging element 303 are incident on the infrared detector 100 in the detector array 301, the incident infrared rays are absorbed by the infrared absorber 101 and converted into heat. This heat is conducted to the temperature detection unit 103 connected to the infrared absorption unit 101. For this reason, the temperature of the temperature detection part 103 on a heat insulation structure rises with the absorbed heat. At this time, the electrical characteristics of the PN junction diode 105 change according to the temperature change. Further, the signal processing circuit unit 302 shown in FIG. 1 reads changes in electrical characteristics for each infrared detector and outputs them to the outside to obtain a thermal image of the subject.

  In addition, the temperature sensitivity of the infrared detector 100 becomes high, so that the electrical characteristic change by the temperature of the PN junction diode 105 is large, and the noise which the PN junction diode 105 generate | occur | produces is small.

  Next, the structure of the temperature detection unit 103 will be described with reference to FIG. The PN junction diode 105 includes a P-type impurity region 306 and an N-type impurity region 307. Further, a plurality of PN junction diodes 105 are connected in series. In addition, the PN junction diodes are connected by the metal wiring layer 104. Here, an insulating film for electrically insulating the metal wiring layer 104 is necessary so that the PN junction diode 105 and the metal wiring layer 104 do not come into contact with each other except a predetermined portion. Therefore, in this embodiment, a thermal oxide film obtained by thermally oxidizing the SOI layer is used as the insulating film. In FIG. 4, the thermal oxide film is shown as an interlayer insulating film 308. Note that a passivation film 309 is stacked on the uppermost layer as a protective film of the temperature detection unit 103.

  According to the present embodiment, since the thermal oxide film is used as the insulating film for electrically insulating the metal wiring layer 104, it is significantly more than the deposited film (silicon oxide film) using the conventional CVD apparatus or the like. A thin film can be formed. In other words, the insulating film on the temperature detection part is thinner than the circuit part and other wiring layer regions, and the insulating film on the temperature detection part is formed by thermally oxidizing the silicon layer. Yes. Therefore, the insulating film deposited on the temperature detection unit can be made thinner than the insulating film formed by deposition by CVD or the like in other regions. Therefore, it is possible to significantly reduce the heat capacity of the temperature detection unit, and it is easy to provide an infrared imaging device that has a faster thermal response speed than conventional ones.

  Furthermore, the insulating film on the temperature detecting portion is used as a thermal oxide film to ensure electrical insulation from the metal wiring layer, and even when the film is thinned, it has sufficient electrical insulation characteristics.

  Further, since the thermal oxidation process is used, the manufacturing process can be easily controlled, and the heat capacity of the insulating film on the temperature detection unit can be manufactured as designed.

  Next, the manufacturing method of the infrared imaging element according to the first embodiment will be described in the order of the manufacturing process with reference to FIGS. 5 to 10 are schematic views of the cross section of the temperature detection unit shown in FIG.

  First, in the first step shown in FIG. 5, an SOI substrate in which a buried silicon oxide film 401 and a single crystal silicon layer 402 (that is, an SOI layer) are sequentially stacked on a single crystal silicon support substrate 400 is prepared as a substrate. .

  In the second step shown in FIG. 6, the separation region 403 is separated into individual infrared detectors 100 by, for example, LOCOS (Local Oxidation of Silicon) separation or STI (Shallow Trench Isolation) separation method similar to the prior art. Form. Here, the isolation region 403 does not reach the buried oxide film layer 401 and is formed between the buried oxide film layer 401 and the isolation region 403 to such a depth that the silicon single crystal region 404 under isolation remains slightly. Specifically, in the case of the LOCOS separation method, the single crystal silicon layer 402 at a position corresponding to the separation region 403 portion is thermally oxidized to form a thermal oxide film. In the STI method, the isolation region 403 portion is silicon etched. The film thickness of the separated silicon single crystal region 404 is preferably as thin as possible in consideration of errors in thermal oxide film and silicon etching.

  Next, an N-type or P-type impurity is implanted to the entire depth of a region to be a detection portion by an ion implantation apparatus or the like to form an impurity region. In this embodiment mode, an N-type low concentration impurity region 405 is formed. Here, the predetermined depth means a depth at which the impurity concentration distribution of the entire SOI layer is uniform.

  In the third step shown in FIG. 7, the P-type high concentration impurity region 406 is implanted to a predetermined depth from, for example, the upper surface of the N-type low concentration impurity region 405. The predetermined depth means a depth at which the depletion layer does not reach the interface with the buried oxide film layer when no bias is applied. The high-concentration impurity region is provided with a P-type for the N-type or an N-type high-concentration impurity region for the P-type so that the concentration is about two orders of magnitude higher than the low-concentration impurity region. Means. After the implantation process, a contact interlayer film 414 is deposited to a film thickness that can sufficiently ensure electrical insulation of the signal processing circuit portion.

  In the fourth step shown in FIG. 8, only the infrared detector 100 is selectively etched. For example, etching is performed using an etching technique having a high etching selectivity with silicon such as hydrofluoric acid. Here, etching is performed until the contact interlayer film 414 and the separation portion 403 are completely removed. However, the region other than the infrared detector 100 such as the contact interlayer 414 on the signal processing circuit portion is etched so that the contact interlayer 414 remains.

  In the fifth step shown in FIG. 9, a thermal oxide film is formed by an oxidation time during which the silicon film in the silicon single crystal region 404 is completely oxidized while the insulating oxide film 408 is separated by thermal oxidation. Subsequently, a contact hole 409 is formed at a predetermined position of the insulating oxide film immediately above the impurity region by using, for example, a dry etching method.

  In the sixth step shown in FIG. 10, a metal wiring layer 410 is formed in order to electrically couple each PN junction diode and the signal processing circuit unit. Of course, the metal wiring layer 410 may be used as a metal silicide film by using a lamp annealing technique or the like. In addition, the metal wiring layer 410 is covered with a passivation film 309.

  Finally, an etching hole 412 is opened at a predetermined position of the insulating film, and an etchant such as TMAH (Tetra-Methyl-Ammonium-Hydroxide) is introduced from the etching hole 412 so as to be hollow inside the single crystal silicon support substrate 400. Forming part. In this way, the infrared imaging element 303 mounted with the infrared detector 100, which is supported by the support body 102 made of an insulating film and in which the temperature detection unit 103 floats in the air, is completed. Such a state is shown in FIGS.

  In the manufacturing method of the infrared imaging device in the present embodiment, unlike the conventional method, the contact interlayer film and the thermal oxide film of the separation part are removed by etching. Further, the contact insulating oxide film in the temperature detection unit is a thermal oxide film. Therefore, it becomes easy to reduce the film thickness of the insulating film to a great extent compared to the conventional case. In particular, since the SOI layer is oxidized using a thermal oxidation method, a dense and thin high-quality insulating layer can be easily formed. In addition, the thickness of the insulating layer can be easily controlled and the film thickness is less likely to vary depending on the location. Therefore, the heat capacity of the temperature detection unit can be greatly reduced.

  Further, as a secondary effect, the insulating film formed immediately above the temperature detecting portion is a thermal oxide film, which is different from a deposited film using a technique such as conventional CVD, and has a stable interface (a semiconductor and an insulating film). Interface). Therefore, noise generated in the diode can be reduced.

  As described above, the infrared detector 300 according to the present embodiment can provide an infrared imaging element that has a small heat capacity, a high thermal response speed, and low noise and is easy to manufacture.

Embodiment 2. FIG.
The structure of the second embodiment is basically the same as the structure of the infrared imaging element shown in the first embodiment, but is characterized in that the connection form of the PN junction diodes constituting the temperature detection unit is different. . That is, although two sets of PN junction diodes are arranged adjacent to each other, one set of diodes and the other set of diodes are electrically separated by PN separation. Also, one and the other diode are connected by a metal film. Furthermore, this metal film is provided on the surface of a recess formed across the PN separation. This embodiment is a feature point different from the first embodiment.

  Hereinafter, the manufacturing method of the infrared imaging element according to the present embodiment will be described in the order of the manufacturing process with reference to FIGS. 11 to 16 are schematic views of a cross section of a temperature detection unit similar to that described in the first embodiment.

  The configuration is the same as that of the first embodiment except for the above feature points. Therefore, in addition to the configuration unique to the present embodiment described below and the effects resulting therefrom, the same effects as in the first embodiment are also exhibited.

  First, in the first step shown in FIG. 11, a so-called SOI substrate in which a buried silicon oxide layer 401 and a single crystal silicon layer 402 (that is, an SOI layer) are sequentially stacked on a single crystal silicon support substrate 400 as a substrate 300. Prepare.

Next, in the second step shown in FIG. 12, the separation region 403 is formed by separation of the individual infrared detectors 100 by, for example, LOCOS separation or STI separation method similar to the prior art. Here, the isolation portion 403 does not reach the buried oxide film layer 401, and the LOCOS separation method can be used up to a depth in which the silicon single crystal region 404 under separation is slightly left between the buried oxide film layer 401 and the separation portion region 403. For example, a thermal oxide film is deposited. If the STI method is used, silicon etching is performed. The film thickness of the silicon single crystal region under separation is preferably as thin as possible in consideration of errors in thermal oxide film and silicon etching.

  Further, an N-type or P-type impurity atom is selectively implanted to a predetermined depth by an ion implantation apparatus or the like so that the region to be the temperature detection unit 103 is formed, and the N-type low concentration impurity region 501 and the P-type low concentration are implanted. An impurity region 502 is formed. Here, the predetermined depth means a depth at which the impurity concentration distribution of the entire SOI layer is uniform.

  Although not shown, a process of forming a region to be the signal processing circuit portion 302 on the substrate 300 is also performed.

  Next, in the third step shown in FIG. 13, the P-type high concentration impurity region 504 is implanted to a predetermined depth from, for example, the upper surface of the N-type low concentration impurity region 501. The predetermined depth means a depth at which the depletion layer does not reach the interface with the buried oxide film layer when no bias is applied. Similarly, the N-type high concentration impurity region 503 is implanted to a predetermined depth of the P-type impurity region 502. Needless to say, 501, 502, 503, and 504 are sequentially formed by, for example, ion implantation using a photolithography technique or the like. The high-concentration impurity region is provided with a P-type for the N-type or an N-type high-concentration impurity region for the P-type so that the concentration is about two orders of magnitude higher than the low-concentration impurity region. Means. After the implantation process, a contact interlayer film 414 is deposited to a film thickness that can sufficiently ensure electrical insulation of the signal processing circuit portion.

  Further, in the fourth step shown in FIG. 14, only the infrared detector 100 is selectively etched using an etching technique having a high etching selectivity with silicon such as hydrofluoric acid. Here, etching is performed until the contact interlayer film 414 and the separation portion 403 are completely removed.

  In the fifth step shown in FIG. 15, the common contact 505 is formed to a predetermined depth in the low concentration impurity regions 501 and 502 by using, for example, a dry etching method. Here, the predetermined depth means a depth that is the least affected by the interface between the buried oxide film layer and the insulating oxide film formed on the upper surface of the SOI, which is generally a noise source. Subsequently, a thermal oxide film is formed on the insulating oxide film 408 by an oxidation time during which the silicon in the silicon single crystal region 404 under isolation is completely oxidized by a thermal oxidation method.

  Subsequently, a contact hole 409 is formed at a predetermined position of the insulating oxide film using a dry etching method immediately above the impurity region. Further, the common contact hole 505 is formed in the low concentration impurity regions 501 and 502. In order to sequentially form the contact holes 409 and 505, a lithography technique or the like commonly used in the semiconductor industry is used.

  Next, in a seventh step shown in FIG. 16, a metal wiring layer 410 is formed in order to electrically couple each PN junction diode and the signal readout circuit. Of course, the metal wiring layer 410 may be used as a metal silicide film by using a lamp annealing technique or the like. The metal wiring layer 410 is covered with an interlayer insulating film 411.

  Finally, an etching hole 412 is opened at a predetermined position of the insulating film, and an etchant such as TMAH (Tetra-Methyl-Ammonium-Hydroxide) is introduced from the etching hole 412 so as to be hollow inside the single crystal silicon support substrate 400. A portion 106 is formed. In this way, the infrared imaging element 303 mounted with the infrared detector 100, which is supported by the support body 102 made of an insulating film and in which the temperature detection unit 103 floats in the air, is completed.

  In the manufacturing method of the infrared imaging element in the present embodiment, unlike the conventional method, the common contact hole is etched to a predetermined depth of 501 and 502, so that in addition to the effect obtained in the first embodiment, distortion due to heat is caused. It is possible to provide an infrared imaging device that is small and further has low noise in the detection unit.

  It should be understood that the above-described embodiment is illustrative in all respects and not restrictive. The scope of the present invention is shown not by the scope of the above-described embodiment but by the scope of the claims, and includes all modifications within the meaning and scope equivalent to the scope of the claims.

DESCRIPTION OF SYMBOLS 100 Infrared detector, 101 Infrared absorption part, 102: Support body, 103: Temperature detection part 104: Metal wiring layer 105: PN junction diode, 106: Hollow part 300: Board | substrate, 301: Detector array, 302: Signal processing circuit , 303: infrared imaging device, 304: SOI layer, 305: buried oxide film layer, 306: P-type impurity region, 307: N-type impurity region, 308: interlayer insulating film, 309: passivation film, 400: support substrate, 401 : Buried oxide film layer, 402: single crystal Si layer, 403: isolation region, 404: Si single crystal region under isolation, 405: N type low concentration impurity layer, 406: P type high concentration impurity layer, 407: etching of isolation part Removal hole, 408: contact thermal oxide insulating film, 409: contact hole, 410: metal wiring layer, 411: passivation 412: Etching hole, 414: Contact interlayer film, 501: N type low concentration impurity layer, 502: P type low concentration impurity layer, 503: N type high concentration impurity layer, 504: P type high concentration impurity layer, 505: Common contact hole.

Claims (5)

A method of manufacturing a thermal-type infrared imaging device having a plurality of pixels and a circuit for reading an electrical signal from the pixels on a main surface of the SOI substrate,
Forming a detection portion for detecting temperature by a silicon diode in the pixel,
In the step of forming the detection unit, a silicon diode is formed on the SOI layer of the SOI substrate, and a surface of the silicon constituting the silicon diode is thermally oxidized to generate a thermal oxide film. A method of manufacturing an infrared imaging device, comprising a step of covering the silicon diode with a buried oxide film layer of an SOI substrate.   As a step of forming the detection portion, the SOI layer was doped with impurities to form a plurality of PN junctions of the silicon diode, and the SOI layer other than the region to be the silicon diode was thermally oxidized, and then generated by this thermal oxidation. 2. The infrared imaging device according to claim 1, wherein the thermal oxide film is etched away to be separated into a plurality of silicon diodes, and then the surface of the silicon diode is thermally oxidized to cover the silicon diode. Method.   As a process of forming the detection part, the SOI layer is doped with impurities to form a plurality of PN junctions of silicon diodes, and the SOI layer other than the region to be a silicon diode is removed by dry etching to be separated into a plurality of silicon diodes. Then, the surface of the silicon diode is thermally oxidized to cover the silicon diode, and the method of manufacturing an infrared imaging device according to claim 1. A thermal infrared imaging device having a plurality of pixels and a circuit for reading out electrical signals from the pixels on the main surface of the SOI substrate,
The pixel includes a detection unit that detects a temperature using a silicon diode, and a support that holds the detection unit away from the semiconductor substrate.
The silicon diode is covered with a buried oxide film layer of the SOI substrate and a thermal oxide film generated by thermally oxidizing the surface of silicon constituting the silicon diode. Infrared imaging device.   A plurality of silicon diodes connected in series to the detection unit, wherein the plurality of silicon diodes are arranged adjacent to each other and electrically separated by PN separation, and a recess is formed across the PN separation; The infrared detection element according to claim 4, wherein the plurality of silicon diodes are connected in series by a metal film provided on the surface of the infrared detection element.

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