Manufacturing method for infrared detection element and infrared detection element

Abstract

To provide a manufacturing method for an infrared detection element that improves the detection characteristics of an infrared detection element.SOLUTION: A manufacturing method for an infrared detection element includes the steps of: patterning an amorphous silicon layer; injecting boron into the amorphous silicon layer and forming an amorphous silicon sacrificial layer that is an amorphous silicon layer not containing boron at the center of the annular amorphous silicon layer; forming a membrane; forming a temperature transducer element on the membrane; forming a coating; forming an infrared absorption film; forming an opening for injecting an etching solution through the insulating film and the membrane in a predetermined area of the amorphous silicon sacrificial layer; and injecting the etching solution through the opening to etch away the amorphous silicon sacrificial layer and a portion of the semiconductor substrate to form a thermal separation chamber.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a method for manufacturing an infrared detector element, and to an infrared detector element. [Background technology]

[0002] In the prior art disclosed in Patent Document 1, a polysilicon layer partially doped with boron is formed on a silicon substrate, and a thermosensitive element (thermopile) is formed on the polysilicon layer. A polysilicon sacrificial layer containing undoped polysilicon is formed in the remaining portion of the polysilicon layer (the central portion of the polysilicon layer). An etching solution is injected into the polysilicon sacrificial layer to remove the polysilicon sacrificial layer and a portion of the silicon substrate, forming a thermal isolation chamber. The thermosensitive element includes a hot junction and a cold junction formed at both ends of the n-type polysilicon, and a hot junction and a cold junction formed at both ends of the p-type polysilicon. The thermoelectromotive force of the entire thermopile is expressed as the sum of the thermoelectromotive force between the two junctions (hot junction and cold junction) in the n-type polysilicon and the thermoelectromotive force of the two junctions (hot junction and cold junction) in the p-type polysilicon. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 07-318417 Summary of the Invention [Problem to be solved by the invention]

[0004] However, in conventional technology, a polysilicon layer is formed on a silicon substrate by implanting boron into polysilicon. Because polysilicon contains multiple crystals (grains) of different sizes, when an etching solution is injected to etch away the polysilicon sacrificial layer, the etching solution penetrates between the grains of different sizes in the polysilicon layer. This can result in large irregularities at the etching interface of the polysilicon layer, i.e., on the surface of the polysilicon layer. The formation of such an irregularity makes the heat transfer between the cold junction and the polysilicon layer unstable. When an infrared detector is miniaturized to improve its spatial resolution, the thermopile linewidth (p-type polysilicon and n-type polysilicon) becomes narrower, resulting in unstable detection characteristics of the infrared detector.

[0005] The present invention has been made to solve the above problems, and an object of the present invention is to provide a method for manufacturing an infrared detection element that improves the detection characteristics of the infrared detection element. [Means for solving the problem]

[0006] In order to achieve the above object, a manufacturing method of an infrared detection element according to an embodiment of the present disclosure includes the steps of depositing an amorphous silicon layer on a surface of a semiconductor substrate and patterning the amorphous silicon layer into a ring shape; injecting boron into the annular amorphous silicon layer and forming an amorphous silicon sacrificial layer in a central portion of the annular amorphous silicon layer, the amorphous silicon layer being an amorphous silicon layer that does not contain boron; forming a membrane containing an etching-resistant material from the surface of the semiconductor substrate to an upper surface of the amorphous silicon layer; forming a temperature sensing element on the membrane;

[0007] An infrared detection element according to an embodiment of the present disclosure comprises: an amorphous silicon layer containing boron formed in a ring shape on the surface of a semiconductor substrate; a membrane extending from the surface of the semiconductor substrate to the upper surface of the amorphous silicon layer; a temperature sensing element formed on the membrane; an insulating film provided on the temperature sensing element and the membrane and covering the temperature sensing element and the membrane; an infrared absorbing film provided on the insulating film at a position corresponding to a heat receiving portion included in the temperature sensing element; an opening penetrating the insulating film and the membrane; and a concave thermal isolation chamber provided in the semiconductor substrate, recessed in the stacking direction of the semiconductor substrate and the membrane, and communicating with the opening. [Effects of the Invention]

[0008] According to the present invention, the detection characteristics of the infrared detection element can be improved. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a front view of an infrared detector element 100 according to an embodiment of the present disclosure. [Figure 2] FIG. 2 is a cross-sectional view taken along line II-II in FIG. [Figure 3] FIG. 3 is a flowchart illustrating a method for manufacturing the infrared detector element 100. [Figure 4] FIG. 4 is a diagram showing an example of the configuration of an infrared detector element 100A according to a comparative example. [Figure 5] FIG. 5 is a diagram showing the irregularities A1 on the surface S1 of the amorphous silicon layer 3b of the infrared detector 100 according to the embodiment of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[0011] Fig. 1 is a front view of an infrared detection element 100 according to an embodiment of the present disclosure, and Fig. 2 is a cross-sectional view taken along line II-II in Fig. 1. The infrared detection element 100 may include a silicon substrate 1, an amorphous silicon sacrificial layer 3a, an amorphous silicon (a-Si) layer 3b, a membrane 4, n-type polysilicon 5a, p-type polysilicon 5b, a thermopile 5, a hot junction 5c, a cold junction 5d, an interlayer insulating film 6, a protective film 7, an opening 8, and an infrared absorbing film 9.

[0012] The infrared detection element 100 may include an amorphous silicon layer 3b containing boron formed in a ring shape on the surface of a silicon substrate 1, a membrane 4 provided from the surface of the silicon substrate 1 to the upper surface of the amorphous silicon layer 3b, and a temperature-sensing element formed on the membrane 4. The infrared detection element 100 may include an interlayer insulating film 6 that is an insulating film provided on the temperature-sensing element and the membrane 4 and covers the temperature-sensing element and the membrane 4, and an infrared absorbing film 9 provided on the insulating film at a position corresponding to a heat-receiving portion included in the temperature-sensing element. The infrared detection element 100 may include an opening 8 that penetrates the interlayer insulating film 6 and the membrane 4, and a concave thermal isolation chamber 2 that is provided in the silicon substrate 1, recessed in the stacking direction of the silicon substrate 1 and the membrane 4, and communicating with the opening 8.

[0013] An amorphous silicon layer 3b implanted with boron is formed in a quadrangular ring shape on the surface of the silicon substrate 1 shown in Fig. 2, as shown in Fig. 1. The silicon substrate 1 may be considered as a semiconductor substrate.

[0014] 2, an amorphous silicon sacrificial layer 3a containing undoped amorphous silicon is formed in the center of the amorphous silicon layer 3b. The amorphous silicon sacrificial layer 3a is removed by etching, which will be described later.

[0015] 2, a membrane 4 containing silicon nitride (SiN) is formed in stages from the surface of the silicon substrate 1 to the upper surface of the amorphous silicon layer 3b. The membrane 4 may be interpreted as a separation film that separates the amorphous silicon layer 3b from the thermopile 5 and separates the silicon substrate 1 from the thermopile 5.

[0016] As shown in FIG. 2, a thermopile 5 is formed above the amorphous silicon layer 3b via a membrane 4. The thermopile 5 may be interpreted as a temperature sensing element. The temperature sensing element may include a hot junction 5c, which is a heat receiving portion, a cold junction 5d provided on the membrane 4 located above the annular amorphous silicon layer 3b, n-type polysilicon 5a, and p-type polysilicon 5b. Specifically, the n-type polysilicon 5a and p-type polysilicon 5b are formed above the membrane 4. The hot junction 5c including aluminum silicon (Al-Si) is provided at one end of these, and the cold junction 5d including aluminum silicon or the like is provided at the other end of these. The thermopile 5 may be configured by interconnecting the n-type polysilicon 5a, p-type polysilicon 5b, hot junction 5c, and cold junction 5d.

[0017] As shown in FIG. 2, an interlayer insulating film 6 is formed on the upper side of the membrane 4, and a protective film 7 is formed on the upper side of the interlayer insulating film 6.

[0018] Openings 8 are formed in predetermined regions of the amorphous silicon sacrificial layer 3a. Specifically, the openings 8 are formed in predetermined regions of the membrane 4, interlayer insulating film 6, and protective film 7 formed above the amorphous silicon sacrificial layer 3a. The openings 8 may be interpreted as cavities that allow the etching solution to reach the amorphous silicon sacrificial layer 3a and the silicon substrate 1. As shown in FIG. 1, the infrared detection element 100 has, for example, four openings 8 formed therein.

[0019] The etching solution introduced through the opening 8 first etches the amorphous silicon sacrificial layer 3a, and then also etches the portion of the silicon substrate 1 directly below this amorphous silicon sacrificial layer 3a. This forms the thermal isolation chamber 2, as shown in Figure 2. The wall surface that forms the thermal isolation chamber 2, i.e., the cross section of the silicon substrate 1 after etching, has a concave shape that is an inverted square pyramid or a truncated square pyramid.

[0020] The shape of the bottom surface of the thermal isolation chamber 2 is determined by the plane orientation of the silicon substrate 1 and the planar shape of the amorphous silicon sacrificial layer 3a. An infrared absorbing film 9 containing gold black (Au-black) is formed on the protective film 7 located above the thermal isolation chamber 2 thus formed.

[0021] Next, a method for manufacturing the infrared detector element 100 will be described with reference to Fig. 3. Fig. 3 is a flowchart for explaining a method for manufacturing the infrared detector element 100.

[0022] In the amorphous silicon layer formation process of step S1, an amorphous silicon layer 3b is deposited on the surface of the silicon substrate 1, and the annular amorphous silicon layer 3b is patterned. Specifically, the amorphous silicon layer 3b is deposited in a predetermined region of the silicon substrate 1 by low-pressure CVD, and the amorphous silicon layer 3b is patterned into a required shape.

[0023] In the boron implantation process of step S2, boron is implanted into the annular amorphous silicon layer 3b, and an amorphous silicon sacrificial layer 3a, which is an amorphous silicon layer 3b that does not contain boron, is formed in the center of the annular amorphous silicon layer 3b. Specifically, boron is implanted into an annular region (periphery of the amorphous silicon layer 3b) in the peripheral portion of the entire region of the amorphous silicon layer 3b, excluding a specific region of the amorphous silicon layer 3b (for example, a region where the thermal isolation chamber 2 is formed). For example, boron is implanted at a dose of 5×10 15 ~1×10 16 (cm -2 ) and then ions are implanted. A specific region of the amorphous silicon layer 3b, i.e., a region closer to the center than the annular region of the amorphous silicon layer 3b, may be considered as a region for forming the thermal isolation chamber 2, and this region becomes the amorphous silicon sacrificial layer 3a made of non-doped amorphous silicon.

[0024] In the membrane formation process of step S3, a film that becomes a membrane containing an etching-resistant material is formed from the surface of the silicon substrate 1 to the upper surface of the amorphous silicon layer 3b. Specifically, SiN that becomes the membrane 4 is deposited at a substrate temperature of about 780°C using a low-pressure CVD method so as to cover the surface of the silicon substrate 1 and the upper surface of the amorphous silicon layer 3b, thereby forming the membrane 4.

[0025] In the polysilicon layer formation process of step S4, a thermosensor element is formed on the membrane 4. Specifically, a polysilicon layer (not shown) that will become the thermosensor element (thermopile 5) is deposited on the membrane 4 using a low-pressure CVD method at a substrate temperature of about 620°C and patterned. In order to improve the electrical conductivity of the polysilicon, a dopant is ion-implanted into the patterned polysilicon layer at a dose of 5×10 15 (cm -2 ) and then electrically activated by annealing at 950° C. for about 20 minutes to form p-type polysilicon 5b and n-type polysilicon 5a. Note that the p-type polysilicon 5b and n-type polysilicon 5a may contain amorphous silicon instead of polysilicon.

[0026] In the interlayer insulating film forming step S5, an insulating film is formed to cover the temperature sensitive element and the membrane 4. Specifically, the interlayer insulating film 6 is deposited on the p-type polysilicon 5b and the n-type polysilicon 5a.

[0027] In the contact hole forming step S6, a contact hole is formed at the connection portion between the p-type polysilicon 5b and the n-type polysilicon 5a.

[0028] In the junction formation process of step S7, Al-Si is deposited by sputtering and patterned to form hot junctions 5c and cold junctions 5d. Then, the hot junctions 5c and cold junctions 5d are mutually connected to the p-type polysilicon 5b and the n-type polysilicon 5a to form the thermopile 5.

[0029] In the protective film forming process of step S8, PSG or SiN is deposited on the thermopile 5 as the protective film 7 by the plasma CVD method.

[0030] In the infrared absorbing film forming step S9, Au-Black is vapor deposited and patterned on the portion of the protective film 7 above the hot junction 5c that serves as the heat receiving portion to form the infrared absorbing film 9.

[0031] In the opening formation process of step S10, openings 8 for injecting an etching solution are formed through the interlayer insulating film 6 and membrane 4 on predetermined regions of the amorphous silicon sacrificial layer. Specifically, openings 8 for forming the thermal isolation chamber 2 are formed by dry etching in the membrane 4, interlayer insulating film 6, and protective film 7 on predetermined regions of the amorphous silicon sacrificial layer 3a.

[0032] In the thermal isolation chamber formation process of step S11, the silicon substrate 1 is etched with the amorphous silicon sacrificial layer 3a and hydrazine through the opening 8 to form the thermal isolation chamber 2. The liquid temperature during etching is approximately 78°C. Note that the temperature-sensing element formed on the membrane 4 is not limited to a thermopile; the diode or bolometer shown in FIG. 4 can also be formed in a similar manner.

[0033] Next, the operation of the infrared detector element 100 will be explained. Incident infrared light absorbed by the infrared absorbing film 9 is converted into heat, raising the temperature of the infrared absorbing film 9. This heat is transferred to the hot junction 5c by conduction, raising the temperature of the hot junction 5c. A portion of the silicon substrate 1 near the hot junction 5c has been removed by etching to form a thermal isolation chamber 2. Therefore, the hot junction 5c and the cold junction 5d are connected only by the highly thermally resistant membrane 4, n-type polysilicon 5a, p-type polysilicon 5b, interlayer insulating film 6, and protective film 7. This makes it difficult for heat from the hot junction 5c to be transferred to the cold junction 5d. As a result, a temperature difference occurs between the hot junction 5c and the cold junction 5d, and an electromotive force is generated in the thermopile 5 by the Seebeck effect. In the configuration of Figure 1, the thermoelectromotive force S of the entire thermopile 5 is the sum of the thermoelectromotive force between the hot junction 5c and the cold junction 5d in the n-type polysilicon 5a and the thermoelectromotive force between the hot junction 5c and the cold junction 5d in the p-type polysilicon 5b, and is expressed by equation (1).

[0034] S=n·α·R th ·P···(1) n is the logarithm of the thermocouple in the thermopile 5, α is the Seebeck coefficient obtained by adding together the n-type polysilicon 5a and the p-type polysilicon 5b, and R th is the thermal resistance and P is the incident energy.

[0035] From equation (1), in order to increase the thermoelectric power S, it is necessary to use a material with a large Seebeck coefficient and to increase the thermal resistance. * is shown in equation (2).

[0036] D * =√[A d / (4kT)]·n·(α·R th / √R d )·(P / P d )···(2) A d is the area of ​​the infrared absorbing film 9, n is the logarithm of the thermocouple, R d is the electrical resistance, P d is the effective incident energy. From equation (2), the figure of merit D *In order to increase the value, it is necessary to increase the area of ​​the infrared absorbing film 9, the number of pairs of thermocouples, the thermal resistance, and the energy transfer efficiency. d needs to be made smaller.

[0037] FIG. 4 is a diagram showing a configuration example of an infrared detection element 100A according to a comparative example. The infrared detection element 100A includes a ring-shaped polysilicon layer 3b1 into which boron is implanted, instead of the amorphous silicon layer 3b described above. Specifically, the infrared detection element 100A includes the polysilicon layer 3b1 formed on the silicon substrate 1 (see FIG. 2), and a temperature-sensing element (thermopile 5) formed on the polysilicon layer 3b1. A polysilicon sacrificial layer into which boron is not implanted is formed in a portion other than a partial region of the polysilicon layer 3b1 (the central portion of the polysilicon layer 3b1). An etching solution is injected into this polysilicon sacrificial layer to remove the polysilicon sacrificial layer and a portion of the silicon substrate 1, thereby forming a thermal isolation chamber 2 (see FIG. 2).

[0038] As described above, in the infrared detector 100A according to the comparative example, the polysilicon layer 3b1 is formed on the silicon substrate 1 by implanting boron into the polysilicon. However, since the polysilicon constituting the polysilicon layer 3b1 contains multiple crystals (grains) of different sizes, when an etching solution is injected to remove the polysilicon sacrificial layer, the etching solution penetrates between the grains contained in the polysilicon. As a result, large irregularities A may be formed on the etching interface of the polysilicon layer 3b1, i.e., on the surface S of the polysilicon layer 3b1.

[0039] When such an etching interface is formed, heat transfer between the cold junction 5d and the polysilicon layer 3b1 becomes unstable. If the infrared detection element 100A is downsized to improve the spatial resolution of the infrared detection element 100A, the line width (p-type polysilicon 5b and n-type polysilicon 5a) of the thermopile 5 becomes narrower, and the unevenness A on the surface S of the polysilicon layer 3b1 causes the detection characteristics of the infrared detection element 100A to become unstable.

[0040] FIG. 5 is a diagram showing the irregularities A1 on the surface S1 of the amorphous silicon layer 3b of the infrared detector 100 according to an embodiment of the present disclosure. Because the infrared detector 100 uses a boron-implanted annular amorphous silicon layer 3b, the amorphous silicon does not have grains like polysilicon, or even if it does have grains, the grains are small. Therefore, when an etching solution is injected to etch away the amorphous silicon sacrificial layer 3a (see FIG. 2), the aforementioned adverse effects caused by the grains are unlikely to occur. In other words, when the amorphous silicon sacrificial layer 3a is removed by the etching solution, the irregularities A1 on the surface S1 of the amorphous silicon layer 3b become smaller, and the surface S1 of the amorphous silicon layer 3b becomes smoother, as shown in FIG. 5.

[0041] The smooth surface S1 of the amorphous silicon layer 3b stabilizes and increases the contact area between the membrane 4 and the amorphous silicon layer 3b. Furthermore, the reduction of the unevenness in the stacking direction makes the film thickness of the membrane 4 uniform, improving the strength of the membrane 4 and further improving the electrostatic breakdown voltage.

[0042] In particular, even if the line width of the thermopile 5 is narrowed in order to miniaturize the infrared detection element 100 and improve the spatial resolution of the infrared detection element 100, the detection characteristics of the infrared detection element 100 are stable because the surface S1 of the amorphous silicon layer 3b is gentle.

[0043] Furthermore, since the etching solution does not penetrate between the grains, it becomes easier to set the position of the surface S1 of the amorphous silicon layer 3b after etching to a specific position. That is, it becomes easier to adjust the width of the amorphous silicon layer 3b, specifically, the width in the orthogonal direction perpendicular to the stacking direction of the membrane 4, interlayer insulating film 6, etc. shown in FIG. 2. This makes it possible to finely adjust the width of the cold junction 5d in the orthogonal direction in accordance with the position of the amorphous silicon layer 3b, thereby significantly improving the detection characteristics of the infrared detection element 100. [Explanation of symbols]

[0044] 1. Silicon substrate 2 Thermal separation chamber 3a Amorphous silicon sacrificial layer 3b1 Polysilicon layer 3b Amorphous silicon layer 4. Membrane 5 Thermopile 5a n-type polysilicon 5b p-type polysilicon 5c hot junction 5d cold junction 6 Interlayer insulating film 7 Protective film 8 Openings 9. Infrared absorbing film 100 Infrared detector element 100A infrared detector

Claims

1. depositing an amorphous silicon layer on a surface of a semiconductor substrate and patterning the amorphous silicon layer into a ring shape; implanting boron into the annular amorphous silicon layer, and forming an amorphous silicon sacrificial layer in a central portion of the annular amorphous silicon layer, the amorphous silicon layer being an amorphous silicon layer not containing boron; forming a membrane including an etching-resistant material from a surface of the semiconductor substrate to an upper surface of the amorphous silicon layer; forming a temperature-sensitive element on the membrane; forming an insulating film over the temperature-sensing element and the membrane; forming an infrared absorbing film on the insulating film at a position corresponding to a heat receiving portion included in the temperature sensing element; forming an opening for injecting an etching solution through the insulating film and the membrane on a predetermined region of the amorphous silicon sacrificial layer; injecting an etching solution through the opening to etch away the amorphous silicon sacrificial layer and a portion of the semiconductor substrate to form a thermal isolation chamber; A method for manufacturing an infrared detection element, comprising:

2. 2. The method for manufacturing an infrared detection element according to claim 1, wherein the temperature-sensing element includes a hot junction which is the heat-receiving portion, and a cold junction which is provided on the membrane located above the annular amorphous silicon layer.

3. an amorphous silicon layer containing boron formed in a ring shape on the surface of a semiconductor substrate; a membrane provided from the surface of the semiconductor substrate to the upper surface of the amorphous silicon layer; and a temperature sensing element formed on the membrane. an insulating film provided on the temperature sensing element and the membrane, covering the temperature sensing element and the membrane; an infrared absorbing film provided on the insulating film at a position corresponding to a heat receiving portion included in the temperature sensing element; an opening penetrating the insulating film and the membrane; a concave thermal isolation chamber provided in the semiconductor substrate, recessed in a stacking direction of the semiconductor substrate and the membrane, and communicating with the opening; An infrared detection element comprising:

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