Plasmonic infrared-wavelength-selective absorber, wavelength-selective infrared sensor, and method for producing plasmonic infrared-wavelength-selective absorber

Abstract

The present invention makes it possible to reliably set an infrared wavelength to be detected by an infrared ray detector such as a thermopile.　This plasmonic infrared-wavelength-selective absorber comprises: a black resist layer that is formed on a silicon wafer and that serves as an infrared absorber made of PMMA and black carbon; and a plasmonic wavelength-selective layer that is formed on the black resist layer, that is constituted by a specific metal, and that transmits only infrared rays of a certain wavelength.

Description

Plasmonics infrared wavelength-selective absorber, wavelength-selective infrared sensor, and method for manufacturing plasmonics infrared wavelength-selective absorber

[0001] The present invention relates to a plasmonics infrared wavelength-selective absorber and the like.

[0002] To detect gases such as carbon dioxide, a plasmonics infrared wavelength-selective absorber that transmits infrared light of a certain wavelength is used. For example, Patent Document 1 discloses an infrared absorber that includes a metal layer, a dielectric layer provided on the metal layer, and a metal nanostructure provided on the dielectric layer, and that can absorb infrared light of a certain wavelength by causing localized surface plasmon resonance in the metal nanostructure with respect to infrared light that satisfies a resonance condition. Patent Document 1 also discloses a thermoelectric conversion element (e.g., a thermopile) that detects infrared light absorbed by the infrared absorber.

[0003] Japanese Patent Application Laid-Open No. 2020-134337

[0004] The technique disclosed in Patent Document 1 has a problem in that it is not possible to reliably set the wavelength of infrared light detected by an infrared detection unit such as a thermopile.

[0005] The present invention has been made in view of the above-mentioned problems, and one of its objects is to make it possible to reliably set the wavelength of infrared rays detected by an infrared detection unit such as a thermopile.

[0006] According to a first aspect of the present invention, a plasmonics infrared wavelength-selective absorber includes a black resist layer formed on a silicon wafer as an infrared absorber made of PMMA and black carbon, and a plasmonics wavelength-selective layer formed on the black resist layer and composed of a predetermined metal, which transmits only infrared light of a certain wavelength. According to a second aspect of the present invention, a plasmonics infrared wavelength-selective absorber includes an infrared absorbing resin layer formed on a silicon wafer as an infrared absorber in which black carbon is dispersed in acrylic resin, and a plasmonics wavelength-selective layer formed on the infrared absorbing resin layer and composed of a predetermined metal, which transmits only infrared light of a certain wavelength. According to a third aspect of the present invention, a wavelength-selective infrared sensor includes the above-mentioned plasmonics infrared wavelength-selective absorber having a black resist layer and a thermopile between the silicon wafer and the black resist layer. According to a fourth aspect of the present invention, a wavelength-selective infrared sensor includes the above-mentioned plasmonics infrared wavelength-selective absorber having an infrared absorbing resin layer and a thermopile between the silicon wafer and the infrared absorbing resin layer. According to a fifth aspect of the present invention, a wavelength-selective infrared sensor comprises the above-mentioned plasmonics infrared wavelength-selective absorber and a pyroelectric infrared detector that detects infrared light selected by the plasmonics infrared wavelength-selective absorber. According to a sixth aspect of the present invention, a method for manufacturing a plasmonics infrared wavelength-selective absorber comprises: coating a silicon wafer with a black resist layer as an infrared absorber made of PMMA and black carbon; forming a metal layer on the black resist layer by sputtering or vapor-depositing any one of aluminum, gold, silver, tungsten, and copper; and applying photolithography and etching to the metal layer so as to transmit infrared light of a certain wavelength. According to a seventh aspect of the present invention, a method for manufacturing a plasmonics infrared wavelength-selective absorber comprises coating a silicon wafer with a black resist layer as an infrared absorber made of PMMA and black carbon; and forming a plasmonics wavelength-selective layer made of any one of aluminum, gold, silver, tungsten, and copper on the black resist layer by a lift-off method.According to an eighth aspect of the present invention, a method for manufacturing a plasmonics infrared wavelength-selective absorber includes forming an infrared absorbing resin layer as an infrared absorber on a silicon wafer, in which black carbon is dispersed in acrylic resin, forming a metal layer on the infrared absorbing resin layer by sputtering or vapor-depositing any one of aluminum, gold, silver, tungsten, and copper, and applying photolithography and etching to the metal layer so as to transmit infrared light of a certain wavelength, thereby forming a plasmonics wavelength-selective layer.

[0007] According to the present invention, the wavelength of infrared light detected by an infrared detecting section such as a thermopile can be reliably set.

[0008] (a) is a cross-sectional view showing a first embodiment of the present invention. (b) is a cross-sectional view showing a second embodiment of the present invention. (c) is a cross-sectional view showing a third embodiment of the present invention. A perspective view showing a plasmonics wavelength selective layer having an MHA structure. (a) to (f) are cross-sectional views showing a manufacturing method of a first embodiment of the present invention in chronological order from (a) to (f). (a) to (g) are cross-sectional views showing a manufacturing method of a second embodiment of the present invention in chronological order from (a) to (g). (a) to (h) are cross-sectional views showing a manufacturing method of a third embodiment of the present invention in chronological order from (a) to (h). (a) is a graph showing infrared transmittance, infrared absorptance, and infrared reflectance in the first embodiment of the present invention. (b) is a graph showing infrared transmittance, etc. in the second embodiment of the present invention. (c) is a graph showing infrared transmittance, etc. in the third embodiment of the present invention. (a) is a cross-sectional view showing a wavelength selective layer of the third embodiment of the present invention when it is present between air layers. 1(b) is a graph showing the infrared transmittance of the wavelength selective layer of 1(a). 1(a) is a configuration diagram of a wavelength selective infrared sensor. 1(b) is a graph showing the signal level of a thermopile of the wavelength selective infrared sensor. 1(a) is a perspective view of a wavelength selective infrared sensor in which a plurality of plasmonics infrared wavelength selective absorbers are arranged. 1(b) is a perspective view showing a plasmonics wavelength selective layer with an MIM structure. 1(c) is a configuration diagram of another embodiment of a wavelength selective infrared sensor. 1(d) is a perspective view showing a plasmonics infrared wavelength selective absorber in which a plasmonics wavelength selective layer is formed on an infrared absorbing resin layer. 1(e) is a graph showing simulation results of the infrared transmittance of a plasmonics wavelength selective layer formed on an infrared absorbing resin layer. 1(f) is a graph showing measurement results of the infrared transmittance of a plasmonics wavelength selective layer formed on an infrared absorbing resin layer. 1(f) is a graph showing an example of a method for manufacturing a plasmonics wavelength selective layer in another embodiment of the present invention.

[0009] An example of an embodiment of the present invention will now be described with reference to the drawings. The components described in this embodiment are merely examples and are not intended to limit the scope of the present invention.

[0010] 1(a) is a cross-sectional view showing an example of the configuration of a plasmonics infrared wavelength-selective absorber (hereinafter referred to as "selective absorber") 1(1) in a first embodiment of the present invention. The selective absorber 1(1) is composed of a thin-film black resist layer 4 formed on a silicon wafer 2 via a thermopile 3, and a plasmonics wavelength-selective layer (hereinafter referred to as "wavelength-selective layer") 5 formed on the black resist layer 4. The thermopile 3 is an example of an infrared detection unit.

[0011] The wavelength-selective infrared sensor (hereinafter referred to as "infrared sensor") 7(1) according to the present invention is composed of the selective absorber 1(1) and a thermopile 3 having a MEMS (Micro Electro Mechanical Systems) structure. The infrared sensor 7(1) is an NDIR (Non Dispersive InfraRed) type sensor.

[0012] The black resist layer 4 contains PMMA (polymethyl methacrylate) and black carbon, and absorbs and transmits infrared rays. The black resist layer 4 functions as an infrared absorber, a heating element, and also as a dielectric. Various commercial products may be used for the black resist layer 4, such as CFPR-BK, a product of Tokyo Ohka Kogyo Co., Ltd. (although not limited to this). CFPR-BK contains 10 to 20 wt% PMMA, 5 to 20 wt% black carbon, 45 to 55 wt% 3-methoxybutyl acetate, 20 to 30 wt% cyclohexane, 5 wt% n-butyl acetate, 5 wt% propylene glycol monomethyl ether acetate, 1 wt% isobutyl alcohol, 1 wt% 2-butanol, and 1 to 10 wt% crosslinker.

[0013] The inventors of the present application measured the infrared reflectance of the black resist layer 4 using Fourier Transform Infrared Spectroscopy (FTIR), and found that the reflectance was 1% to 0.01% at infrared wavelengths from 0.78 μm (the shortest infrared wavelength) to 15.0 μm. Furthermore, when the reflectance and transmittance of a 1.2 μm-thick black resist layer 4 were measured, the reflectance was 1.0% to 0.01% and the transmittance was 14% at infrared wavelengths from 0.78 to 15.0 μm. Therefore, the absorptance of the 1.2 μm-thick black resist layer 4 was 85% or more (85.99% or less). That is, the absorptance was 85% or more (85.99% or less) at the infrared wavelength of 4.26 μm corresponding to carbon dioxide, the infrared wavelength of 4.8 μm corresponding to carbon monoxide, and the infrared wavelengths of 2.7 or 6.3 μm corresponding to water vapor. However, it is believed that the absorptance increases as the thickness of the black resist layer 4 increases. Therefore, the black resist layer 4 sufficiently absorbs infrared rays, and the thermopile 3 provided below the black resist layer 4 can effectively detect the amount of infrared rays.

[0014] The wavelength selection layer 5 is made of any one of metals such as aluminum, gold, silver, tungsten, copper, etc., or a combination of these metals, and has a metal hole array (MHA) structure having holes 6. The wavelength selection layer 5 is a plasmonics structure in which surface plasmons (SPs) are generated at the interface between the metal and the dielectric, and can regulate the transmitted infrared wavelength by generating surface plasmon resonance for infrared rays that satisfy the resonance conditions.

[0015] 2 is a perspective view showing an example of the configuration of a wavelength selection layer 5 having an MHA structure having a plurality of holes 6 at a predetermined pitch P. The transmitted infrared wavelength λspp of this wavelength selection layer 5 will be described below.

[0016] For the example configuration of FIG. 2, the transmitted infrared wavelength λspp determined by the action of SP is shown in equation (1). In formula (1), P is the pitch of the holes in the MHA, εm is the dielectric constant of the metal, εd is the dielectric constant of the dielectric, and i and j are integers. That is, the transmitted infrared wavelength λspp is determined by the pitch P. That is, the wavelength selection layer 5 has a shape that allows only infrared light of a certain wavelength to pass through.

[0017] As shown in equations (2) to (4), equation (1) is derived from the fact that Ksp, the wave number of the SP, and Kx, the wave number of the diffracted light in the surface direction, are equal.

[0018] <Configuration of Second Embodiment> Fig. 1(b) is a cross-sectional view showing an example of the configuration of a selective absorber 1(2) in a second embodiment of the present invention. Similar to the selective absorber 1(1), the selective absorber 1(2) comprises a black resist layer 4 and a wavelength selection layer 5 on a silicon wafer 2 via a thermopile 3. The selective absorber 1(2) further comprises a dielectric layer 8 in the hole 6 and on the wavelength selection layer 5. The dielectric layer 8 is made of, for example, silicon dioxide (SiO ２ The selective absorber 1 (2) is formed by sputtering. The method for manufacturing the selective absorber 1 (2) will be described in detail later.

[0019] The infrared sensor 7(2) according to the present invention is composed of the selective absorber 1(2) and the thermopile 3. The dielectric layer 8 is made of aluminum oxide (Al ２ O ３ ), silicon nitride (Si ３ N ４ ), silicon (Si), zirconium oxide (ZrO ２ ), titanium oxide (TiO ２ ) etc.

[0020] <Configuration of Third Embodiment> Fig. 1(c) is a cross-sectional view showing an example of the configuration of a selective absorber 1(3) in a third embodiment of the present invention. Similar to the selective absorber 1(1), the selective absorber 1(3) comprises a black resist layer 4 and a wavelength selection layer 5 on a silicon wafer 2 via a thermopile 3. The selective absorber 1(3) further comprises a dielectric layer 8 made of the same components as the selective absorber 1(2) between the black resist layer 4 and the wavelength selection layer 5, in the hole 6, and on the wavelength selection layer 5. Details of a manufacturing method for the selective absorber 1(3) will be described later.

[0021] The infrared sensor 7 ( 3 ) according to the present invention is composed of the selective absorber 1 ( 3 ) and the thermopile 3 .

[0022] <Manufacturing Method> The manufacturing method of the selective absorbers 1(1) to 1(3) will be explained below in chronological order. The case where a black resist is formed on a silicon wafer and a thermopile is omitted will be explained. Each manufacturing method is an example, and there is no particular limitation as long as it can form the selective absorbers 1(1) to 1(3).

[0023] <Manufacturing Method of Selective Absorber 1(1)> The selective absorber 1(1) is formed by the manufacturing method shown in FIG. 3. First, as shown in FIG. 3(a), a black resist layer 4 is formed on a silicon wafer 2 by, for example, spin coating. As shown in FIG. 3(b), a metal layer 5r of aluminum, for example, 150 nm thick, is sputtered onto the black resist layer 4. As shown in FIG. 3(c), an upper cover layer 9 is coated on the metal layer 5r. The upper cover layer 9 may be, for example, a product manufactured by Tokyo Ohka Kogyo Co., Ltd. under the trade name TSMR. Next, as shown in FIG. 3(d), a plurality of preliminary holes 10 are formed in the upper cover layer 9 by photolithography.

[0024] After photolithography, as shown in FIG. 3( e), the metal layer 5 r is etched by ion beam milling, and the preliminary hole 10 is enlarged to the metal layer 5 r. The enlarged portion of the preliminary hole 10 forms the hole 6.

[0025] For example, a test was conducted to form a hole 6 in an aluminum layer by photolithography using an MLA150 manufactured by Heidelberg Instruments Co., Ltd., and the results showed that the laser wavelength was 405 nm and the dose was 150 mJ / cm. ２ At defocus values ​​of -2 and -4, good holes 6 could be formed. ２ At defocus values ​​of 0, -2, and -4, the hole 6 could be formed. ２ At a defocus value of 0, a hole 6 could be formed. On the other hand, at a laser wavelength of 405 nm and a dose of 110 mJ / cm ２ At defocus values ​​of 0 and -2, hole 6 could not be formed.

[0026] As a result of performing hole processing on the metal layer 5r using an ion beam milling device, when the diameter D1 of the holes 6 was 1.7 μm, the holes 6 could be formed when the pitch P of the holes 6 was 2.7 μm, 3.1 μm, 3.6 μm, and 4.1 μm. Furthermore, when the diameter D1 of the holes 6 was 2.3 μm, the holes 6 could be formed when the pitch P was 3.6 μm. On the other hand, when the diameter D1 of the holes 6 was 1.4 μm and the pitch P was 3.6 μm, some holes 6 could not be clearly formed among the multiple holes 6. In other words, the holes 6 could be formed when the diameter D1 was 1.7 μm or more and 2.3 μm or less and the pitch P was 2.7 μm or more and 4.1 μm or less.

[0027] Finally, the upper cover layer 9 is removed to form the selective absorber 1(1) having the wavelength selective layer 5 with the plurality of holes 6 at pitch P exposed, as shown in FIG. 3(f).

[0028] <Manufacturing Method of Selective Absorber 1(2)> The selective absorber 1(2) is formed by the manufacturing method shown in Figure 4. The processing details of the steps in Figures 4(a) to (f) may be the same as the steps in Figures 3(a) to (f) for the selective absorber 1(1). In the selective absorber 1(2), as shown in Figure 4(g), a 300 nm thick silicon dioxide is sputtered into the holes 6 and on the wavelength selection layer 5 to provide a dielectric layer 8. This forms the selective absorber 1(2) having a plurality of holes 6 at a pitch P.

[0029] <Manufacturing Method of Selective Absorber 1 (3)> The selective absorber 1 (3) is formed by the manufacturing method shown in Figure 5. First, as shown in Figure 5(a), a black resist layer 4 is coated on a silicon wafer 2. As shown in Figure 5(b), a 300 nm thick silicon dioxide is sputtered on the black resist layer 4 to form a dielectric layer 8. As shown in Figure 5(c), a 150 nm thick aluminum metal layer 5r is sputtered on the dielectric layer 8. As shown in Figure 5(d), a top cover layer 9 made of, for example, a material with the product name TSMR is coated on the metal layer 5r.

[0030] Next, as shown in FIG. 5( e), a plurality of preliminary holes 10 are formed in the top cover layer 9 by photolithography. After photolithography, as shown in FIG. 5( f), the metal layer 5r is etched by ion beam milling, and the preliminary holes 10 are enlarged into the metal layer 5r. The enlarged portions of the preliminary holes 10 form holes 6. The top cover layer 9 is then removed, and as shown in FIG. 5( g), the wavelength selection layer 5 is formed, exposing a plurality of holes 6 at a pitch P. Finally, as shown in FIG. 5( h), silicon dioxide is sputtered to a thickness of 300 nm in the holes 6 and on the wavelength selection layer 5, thereby enlarging the thickness of the dielectric layer 8 and forming a selective absorber 1 (3) having a plurality of holes 6 at a pitch P.

[0031] <FEM (Finite Element Method)> The results of FEM analysis of the selective absorber of the present invention are described below. Assuming that the black resist layer 4 is PMMA, a simulation was performed on the relationship between the wavelength of infrared light and the transmittance, absorptance, and reflectance. The simulation conditions were: metal thickness: 150 nm, PMMA thickness: 300 nm, silicon dioxide thickness: 300 nm, hole pitch P: 3.6 μm, and hole diameter: 1.7 μm.

[0032] <Simulation Results for Selective Absorber 1(1)> The simulation results for Selective Absorber 1(1) are shown in Figure 6(a). At an infrared wavelength of around 3.9 µm, the transmittance or absorptance increases significantly, and the reflectance decreases significantly. In other words, the results show that Selective Absorber 1(1) can transmit or absorb infrared light of a certain wavelength without reflecting it, and guide it to the black resist layer 4. Therefore, the thermopile 3 provided below the black resist layer 4 can detect infrared light of a certain wavelength. Note that 85% or more of the infrared light transmitted or absorbed by Selective Absorber 1(1) is absorbed by the black resist layer 4 and detected by the thermopile 3.

[0033] <Simulation Results of Selective Absorbent 1 (2)> The simulation results of the selective absorbent 1 (2) are shown in FIG. 6(b). ２ In the vicinity of the wavelength of 4.26 μm of infrared light absorbed by carbon dioxide, the transmittance and absorptance are significantly high, and the reflectance is significantly low. Therefore, the thermopile 3 can select and detect infrared light of a wavelength corresponding to carbon dioxide.

[0034] <Simulation Results for Selective Absorber 1 (3)> The simulation results for Selective Absorber 1 (3) are shown in Figure 6(c). Around an infrared wavelength of 4.4 µm, the transmittance and absorptance are significantly high, and the reflectance is significantly low. Therefore, the thermopile 3 can detect infrared rays of a certain wavelength.

[0035] In relation to the selective absorber 1 (3), a simulation was performed on the model shown in Figure 7(a) in which air layers 5a are provided above and below the wavelength selection layer 5. As shown in Figure 7(b), the transmittance is significantly high in the vicinity of the 4.26 μm wavelength of infrared light absorbed by carbon dioxide. This simulation revealed that it is possible to selectively detect infrared light of a certain wavelength corresponding to carbon dioxide.

[0036] <Principle of Infrared Sensor> The principles of the infrared sensor 7(1) formed using selective absorber 1(1), the infrared sensor 7(2) formed using selective absorber 1(2), and the infrared sensor 7(3) formed using selective absorber 1(3) will be described below with reference to Figure 8(a). These infrared sensors 7(1) and the like are used together with an emitter 11 that irradiates infrared light and an infrared passage 12. The passage 12 is provided with a gas inlet 13 and an outlet 14. In the infrared sensor 7(1) and the like shown in Figure 8(a), the silicon wafer 2 and the thermopile 3 are integrally formed.

[0037] When the infrared sensor 7(1) or the like is activated, infrared rays are irradiated from the emitter 11 toward the wavelength selection layer 5 in the passage 12. Of the irradiated infrared rays, those with a wavelength selected by the wavelength selection layer 5 reach the black resist layer 4 and are absorbed. The thermopile 3 detects the infrared rays absorbed by the black resist layer 4. Meanwhile, gas outside the passage 12 flows in through the inlet 13 and flows out through the outlet 14.

[0038] The following describes a case where the wavelength selection layer 5 is configured to transmit or absorb only infrared light with a wavelength of 4.26 μm, which corresponds to carbon dioxide. In this case, the thermopile 3 detects only infrared light with a wavelength of 4.26 μm. When carbon dioxide is generated around the infrared path 12, the carbon dioxide flows in through the inlet 13 and flows out through the outlet 14. The infrared light with a wavelength of 4.26 μm among the infrared light emitted from the emitter 11 is absorbed by the carbon dioxide. Therefore, as shown in FIG. 8( b), the signal level, which is the amount of infrared light with a wavelength of 4.26 μm detected by the thermopile 3, decreases when carbon dioxide flows in. This allows the thermopile 3 to detect carbon dioxide.

[0039] Carbon monoxide (CO) absorbs infrared light at a wavelength of 4.8 μm, so carbon monoxide can be detected by configuring the wavelength selection layer 5 to transmit or absorb only infrared light with a wavelength of 4.8 μm. Interference gas (water vapor) absorbs infrared light at a wavelength of 2.7 or 6.3 μm, so interference gas can be detected by configuring the wavelength selection layer 5 to transmit or absorb infrared light with a wavelength of 2.7 or 6.3 μm. The pitch P of the MHA is determined by substituting the infrared wavelength to be detected for λspp in equation (1). In other words, by setting the pitch P and forming the wavelength selection layer 5, an infrared sensor 7(1) or the like that can detect infrared light of a certain wavelength can be formed.

[0040] <Actions and Effects of the Embodiment> According to the selective absorbers 1(1) to (3) of the present embodiment, a black resist layer 4 is provided below the wavelength selection layer 5, and 85% or more of the infrared rays of a certain wavelength that are transmitted through the wavelength selection layer 5 are absorbed by the black resist layer 4. As a result, by setting the wavelength selection layer 5 so that only infrared rays of a certain wavelength are transmitted, it is possible to reliably guide the infrared rays of the certain wavelength to the thermopile 3 via the black resist layer 4. This makes it possible to reliably set the wavelength of the infrared rays to be detected by the thermopile 3. Furthermore, by having the black resist layer 4, the infrared sensor 7(1) and the like configured using the selective absorbers 1(1) to (3) can reliably detect only infrared rays of a certain wavelength.

[0041] The metal constituting the wavelength selection layer 5 of the selective absorbers 1(1) to 1(3) is aluminum, gold, silver, tungsten, or copper, which is a metal that reliably generates plasmons. This allows infrared rays of a certain wavelength to be reliably absorbed using plasmons, and the thermopile 3 can reliably detect only infrared rays of a certain wavelength.

[0042] Furthermore, the black resist layer 4 is a dielectric layer that functions as an infrared absorber and also as a dielectric that generates plasmons at the interface with the metal. This allows plasmons to be used to absorb only infrared rays of a certain wavelength even when the wavelength selection layer 5 uses a selective absorber 1(1) that does not contain a dielectric. This allows the selective absorber 1(1) to be formed compactly, and the infrared sensor 7(1) to be formed compactly.

[0043] Furthermore, since the wavelength selection layer 5 has an MHA structure, the pitch P of the holes 6 corresponding to the transmitted infrared wavelength λspp can be determined using the above-mentioned formula (1). This makes it possible to set the wavelength of infrared light to be detected by determining the MHA pitch P. This makes it possible to form the selective absorbers 1(1) and the like for detecting infrared light of different wavelengths on one silicon wafer 2, and to form an infrared sensor that can detect infrared light of multiple wavelengths using only one wafer process.

[0044] For example, the infrared sensor 7-1 shown in FIG. 9 can be easily formed by using an MHA structure for the wavelength selection layer 5. The shape and number of MHA structures arranged in an infrared sensor that can be easily formed using an MHA structure are not limited. In the infrared sensor 7-1, the selective absorber 1 (3) in the upper right of FIG. 9 absorbs 4.26 μm infrared light corresponding to carbon dioxide, the selective absorber 1 (3) in the lower right absorbs 4.8 μm infrared light corresponding to carbon monoxide, the selective absorber 1 (3) in the lower left absorbs 2.7 or 6.3 μm infrared light corresponding to interference gases, and the selective absorber 1 (3) in the upper left can absorb infrared light of other wavelengths. Thus, by adjusting the pitch P for each wavelength selection layer 5, an infrared sensor 7-1 that can detect carbon dioxide, carbon monoxide, interference gases, and other gases can be easily formed. This configuration can also be considered a plasmonics infrared wavelength selective absorber configuration in which multiple wavelength selection layers 5 that transmit infrared light of different wavelengths are formed on a silicon wafer 2 (on one silicon wafer 2). Although the selective absorber 1 (3) is used here, other selective absorbers 1 may be used. Also, a combination of these may be used.

[0045] Furthermore, according to the manufacturing method of the selective absorber 1(1), etc., a black resist layer is formed by coating, a metal layer is formed by sputtering or vapor deposition, and a wavelength selection layer is formed on the metal layer by photolithography and etching. Therefore, by setting the thickness using a device that forms each layer, such as a coating device, the selective absorber 1(1), etc. can be formed easily and reliably.

[0046] Furthermore, according to the manufacturing method of the selective absorber 1(1), etc., aluminum or the like, which is easy to sputter or vapor-deposit, is used as the metal layer, so that the metal layer can be formed easily and accurately. As a result, the wavelength selection layer 5 can be accurately formed by processing the metal layer.

[0047] Furthermore, according to the manufacturing method of the selective absorber 1(1), etc., it is possible to form a single infrared sensor capable of detecting infrared rays of a plurality of wavelengths by forming a plurality of wavelength selection layers 5 that transmit infrared rays of different wavelengths on a single silicon wafer 2. Therefore, the formed infrared sensor can detect a plurality of types of gases, such as carbon dioxide or carbon monoxide, using compact equipment.

[0048] 10 is a diagram showing an example of a schematic configuration of a selective absorber 1 (4) in another embodiment of the present invention. The selective absorber 1 (4) may be a selective absorber having a wavelength selection layer 15 with an MIM (Metal Insulator Metal) structure and a black resist layer 4 provided under the wavelength selection layer 15.

[0049] The wavelength selection layer 15 is composed of a lower metal layer 16, a dielectric layer 17 on the lower metal layer 16, and a metal patch 18 on the dielectric layer 17. The materials of the lower metal layer 16 and the metal patch 18 are the same as the metal of the wavelength selection layer 5, and the material of the dielectric layer 17 is the same as the dielectric layer 8.

[0050] The transmitted infrared wavelength λr of the wavelength selection layer 15 is determined by equation (5). In equation (5), D2 is the diameter of the metal patch, and n ｄ is the refractive index of the dielectric, c is the velocity of free space, and ω ｐis the plasma frequency of the metal, and d is the thickness of the dielectric. That is, the transmitted infrared wavelength λr is determined by the diameter D2 of the metal patch and the thickness d of the dielectric.

[0051] Adjusting the transmitted infrared wavelength λr is difficult because it requires adjusting the lithography or etching method to change the diameter D2 or thickness d. In particular, forming multiple selective absorbers 1(4) that absorb infrared rays of different wavelengths by adjusting the thickness d in a single wafer process is difficult because it requires adjusting the film thickness for each selective absorber 1(4). Furthermore, the different film thicknesses for each selective absorber 1(4) make it difficult to form a compact infrared sensor. In contrast, a selective absorber 1(1) or the like having a wavelength selection layer 5 with an MHA structure can change the transmitted infrared wavelength λspp by adjusting the pitch P, making it easy to form an infrared sensor that can detect infrared rays of multiple wavelengths in a single wafer process. Furthermore, because the transmitted infrared wavelength λspp can be changed by adjusting the pitch P of the selective absorber 1(1), the thickness of multiple selective absorbers 1(1) or the like formed in a single wafer process is uniform, allowing for the formation of a compact infrared sensor. For this reason, a selective absorber 1(1) or the like having a wavelength selection layer 5 is more preferable.

[0052] Similar to the selective absorbers 1(1) to (3), the selective absorber 1(4) having the wavelength selection layer 15 of this embodiment can reliably absorb and detect infrared rays of a certain wavelength by having the black resist layer 4. Furthermore, similar to the selective absorbers 1(1) to (3), the metal constituting the wavelength selection layer 5 is aluminum or the like, which is a metal in which plasmons are reliably generated, and therefore infrared rays of a certain wavelength can be reliably absorbed by utilizing plasmons.

[0053] <Another Embodiment of Infrared Sensor> FIG. 11 is a diagram showing an example of the configuration of an infrared sensor 7(4), which is another embodiment of the infrared sensor of the present invention. The infrared sensor 7(4) has a pyroelectric infrared detecting element 20 as an infrared detecting unit, at the same position as the silicon wafer 2 and thermopile 3 of the infrared sensors 7(1) to 7(3) in FIG. 8(a). The pyroelectric infrared detecting element 20 is a detecting element that generates a pyroelectric voltage due to the pyroelectric effect in response to the amount of infrared light, and has been conventionally used, for example, as a human presence sensor. The pyroelectric infrared detecting element 20 is formed, for example, by integrating a pyroelectric element (the pyroelectric element may also be considered the infrared detecting unit) with a silicon wafer as a base material. The pyroelectric infrared detecting element 20 rapidly generates or changes voltage in response to the amount of infrared light. Therefore, the infrared sensor 7(4) equipped with the pyroelectric infrared detecting element 20 can rapidly detect gases such as carbon dioxide.

[0054] 12 is a diagram showing an example of the schematic configuration of a selective absorber 1 (5) according to another embodiment of the present invention. The selective absorber 1 (5) has an infrared absorbing resin layer 50 as an infrared absorber, and a wavelength selection layer 51 formed on the infrared absorbing resin layer 50.

[0055] The infrared absorbing resin layer 50 is formed on the silicon wafer 2 by mixing and dispersing black carbon particles with particle sizes of 20 nm to 100 nm in an acrylic resin. The wavelength selection layer 51 has an MHA structure with holes 6 and includes a transparent dielectric layer 52. The wavelength selection layer 51 is made of any metal such as aluminum, gold, silver, tungsten, or copper, or a combination of these metals. The wavelength selection layer 51 is a plasmonics structure in which SP occurs at the interface between the metal and the dielectric, and can generate surface plasmon resonance to restrict the transmitted infrared rays to only infrared rays of a certain wavelength. The dielectric layer 52 is made of silicon dioxide (SiO ２ ) is composed of

[0056] The infrared absorbing resin layer 50 and the wavelength selection layer 51 function as a metal hole array resin laminated infrared absorber, and by integrating them into a thermopile chip, for example, the optical filter and thermopile can be integrated. This allows for miniaturization and thinning. Furthermore, it is possible to form a compact selective absorber on the silicon wafer 2 (on one silicon wafer 2) in which multiple wavelength selection layers 51 that transmit infrared rays of different wavelengths are formed.

[0057] 13 shows the results of a transmittance simulation performed by FEM (using COMSOL Multiphysics) on a wavelength selective layer 51 combined with a dielectric layer 52. In the simulation, the material of the MHA structure was aluminum, the pitch P was 3.75 μm, and the refractive index was based on the Drude model. The refractive index of the silicon dioxide of the dielectric layer 52 was 1.46 or less.

[0058] The results of this simulation showed that the transmittance was significantly higher in the vicinity of the 4.26 μm wavelength of infrared light absorbed by carbon dioxide. This simulation revealed that it was possible to selectively transmit infrared light of a certain wavelength corresponding to carbon dioxide.

[0059] Furthermore, when the infrared absorbing resin was measured for its infrared absorptivity by FTIR without laminating MHA, it absorbed more than 70% of mid-infrared rays between 2 μm and 8 μm, and its absorptivity at 4.3 μm, near the infrared wavelength of 4.26 μm, was 85%. This measurement revealed that the infrared absorbing resin can absorb infrared rays of a certain wavelength corresponding to carbon dioxide. The absorptivity was calculated by subtracting the infrared reflectance and the transmittance of the infrared absorbing resin from 100%.

[0060] FIG. 14 shows the results of FTIR measurements of the transmittance of MHA due to plasmon excitation at the boundary between silicon dioxide and aluminum. In the graph of FIG. 14, the solid line indicates the case where a silicon dioxide film is not present on the upper surface, and the dashed line indicates the case where a silicon dioxide film is present on the upper surface. When a silicon dioxide film is present on the upper surface, the transmittance peaked at a wavelength of 5.0 μm (the absorptance can be estimated to be 43%). Furthermore, when a silicon dioxide film is not present on the upper surface, the transmittance peaked at wavelengths of 3.7 μm and 4.8 μm (the absorptance at a wavelength of 3.7 μm can be estimated to be 44%). In both cases, as with the simulation results (shown in FIG. 13), there was a transmittance peak, which proved to be effective in selecting a specific wavelength. It was also found that the wavelength at which the transmittance peaked differed between the case where a silicon dioxide film was present and the case where it was not present. This makes it possible to regulate the wavelength of the infrared light transmitted by selecting whether or not there was a silicon dioxide film on the upper surface.

[0061] 15A and 15B are diagrams showing an example of a method for manufacturing a wavelength selection layer 51 according to another embodiment of the present invention. First, as shown in FIG. 15A, a 1 μm-thick dielectric layer 52 made of silicon dioxide is formed on a silicon wafer 2. As shown in FIG. 15B, a 150 nm-thick metal layer 5r made of aluminum is sputtered on the dielectric layer 52. As shown in FIG. 15C, a top cover layer 9 is coated on the metal layer 5r by TSMR patterning. A plurality of preliminary holes 10 are formed in the top cover layer 9.

[0062] Next, as shown in FIG. 15(d), the metal layer 5r is ２ / BCL ３ The preliminary holes 10 are then etched to enlarge them down to the metal layer 5r. The enlarged portions of the preliminary holes 10 form holes 6. The top cover layer 9 is then removed to expose the holes 6 at a pitch P, as shown in FIG. 15( e), and form the wavelength selection layer 51. Furthermore, as shown in FIG. 15( f), a transparent dielectric layer 53 made of silicon dioxide and having a thickness of 1 μm may be formed on the wavelength selection layer 51.

[0063] Although the embodiments of the present invention have been described above with reference to the drawings, the present invention is not limited to those shown in the drawings.

[0064] For example, the wavelength selection layer may have an inverted structure of a metal hole array. The inverted structure of a metal hole array is a structure in which the inverted uneven shape of a metal hole array is periodically arranged at a constant pitch. The inverted structure of a metal hole array can transmit only infrared rays of a certain wavelength by utilizing the extraordinary light transmission phenomenon. In this case, since the wavelength of the infrared rays to be detected can be set, selective absorbers for detecting infrared rays of different wavelengths can be easily formed on a single silicon wafer.

[0065] Furthermore, a layer of PMMA that does not contain black carbon may be provided on the side or top surface of the wavelength selective layer 5. Even in this case, by providing a black resist layer below the wavelength selective layer, infrared rays of a certain wavelength can be reliably absorbed, thereby providing an effect that the wavelength of infrared rays that can be detected can be easily set.

[0066] PMMA is highly transparent and has a high infrared transmittance (approximately 92%), so a PMMA layer without black carbon transmits infrared rays without absorbing them, allowing the infrared rays to reliably enter the black resist layer 4. In addition, the wavelength selection layer 5 can be protected by the solid PMMA layer.

[0067] Furthermore, the method for producing a selective absorber of the present invention may be a method in which a black resist layer is formed on a silicon wafer, and then a wavelength selection layer made of a metal is formed on the black resist layer by a lift-off method. In this case, the metal is aluminum, gold, silver, tungsten, copper, or a combination of these metals. As the lift-off method, for example, a method can be adopted in which a photoresist layer patterned by photolithography is formed on the black resist layer, a metal is sputtered or vapor-deposited on the photoresist layer, and then the portion where the metal layer is stacked on the top surface of the photoresist layer is removed by etching, thereby forming a wavelength selection layer made of the remaining metal.

[0068] According to the manufacturing method of the selective absorber using the lift-off method, the wavelength selective layer can be easily formed without etching the metal layer, and therefore, the selective absorber having the black resist layer can be easily formed at low cost.

[0069] Alternatively, multiple wavelength selection layers that transmit infrared rays of different wavelengths may be formed on a single silicon wafer using the lift-off method, and in this case, each wavelength selection layer can be formed without etching the metal layer, making it possible to easily and inexpensively form a single infrared sensor that can detect infrared rays of multiple wavelengths.

[0070] 1 (1), 1 (2), 1 (3), 1 (4), 1 (5): Selective absorber (plasmonics infrared wavelength selective absorber) 2: Silicon wafer, 3: Thermopile (infrared detection unit), 4: Black resist layer, 5: Wavelength selective layer (plasmonics wavelength selective layer), 5a: Air layer, 5r: Metal layer, 6: Hole 7 (1), 7 (2), 7 (3), 7-1: Infrared sensor (wavelength selective infrared sensor) 8: Dielectric layer, 9: Upper cover layer, 10: Spare hole, 11: Emitter, 12: Passage, 13: Inlet, 14: Outlet P: Pitch, D1: Diameter 15: Wavelength selective layer (plasmonics wavelength selective layer) 16: Lower metal layer, 17: Dielectric layer, 18: Metal patch D2: Diameter, d: Thickness 7 (4): Infrared sensor (wavelength selective infrared sensor), 20: Pyroelectric infrared detector (infrared detection unit) 50: infrared absorbing resin layer, 51: wavelength selection layer (plasmonics wavelength selection layer), 52, 53: dielectric layers

Claims

1. A plasmonics infrared wavelength-selective absorber comprising: a black resist layer formed on a silicon wafer as an infrared absorber made of PMMA and black carbon; and a plasmonics wavelength-selective layer formed on the black resist layer, made of a predetermined metal and allowing only infrared light of a certain wavelength to pass through.

2. The plasmonics infrared wavelength-selective absorber according to claim 1, wherein the predetermined metal is any one of aluminum, gold, silver, tungsten, and copper.

3. The plasmonics infrared wavelength-selective absorber according to claim 1, wherein the black resist layer is a dielectric layer.

4. The plasmonics infrared wavelength-selective absorber according to claim 1, wherein the plasmonics wavelength-selective layer has a metal hole array structure or an inverted metal hole array structure.

5. The plasmonics infrared wavelength-selective absorber according to claim 1, wherein a layer of PMMA containing no black carbon is provided on a side or top surface of the plasmonics wavelength-selective layer.

6. The plasmonics infrared wavelength-selective absorber according to claim 1, wherein a plurality of plasmonics wavelength-selective layers that transmit infrared rays of different wavelengths are formed on the silicon wafer.

7. A plasmonics infrared wavelength selective absorber comprising: an infrared absorbing resin layer formed on a silicon wafer as an infrared absorber in which black carbon is dispersed in acrylic resin; and a plasmonics wavelength selective layer formed on the infrared absorbing resin layer and made of a predetermined metal, through which only infrared rays of a certain wavelength can pass.

8. A wavelength-selective infrared sensor comprising: a plasmonics infrared wavelength-selective absorber according to any one of claims 1 to 6; and a thermopile between the silicon wafer and the black resist layer.

9. A wavelength-selective infrared sensor comprising: a plasmonics infrared wavelength-selective absorber according to any one of claims 1 to 7; and a pyroelectric infrared detector that detects infrared light selected by the plasmonics infrared wavelength-selective absorber.

10. A wavelength-selective infrared sensor comprising: the plasmonics infrared wavelength-selective absorber according to claim 7; and a thermopile between the silicon wafer and the infrared absorbing resin layer.

11. A method for manufacturing a plasmonics infrared wavelength-selective absorber, comprising: coating a silicon wafer with a black resist layer as an infrared absorber made of PMMA and black carbon; forming a metal layer on the black resist layer by sputtering or vapor-depositing any one of aluminum, gold, silver, tungsten, and copper; and applying photolithography and etching to the metal layer to form a plasmonics wavelength-selective layer so as to transmit infrared light of a certain wavelength.

12. A method for manufacturing a plasmonics infrared wavelength-selective absorber, comprising: coating a silicon wafer with a black resist layer as an infrared absorber made of PMMA and black carbon; and forming a plasmonics wavelength-selective layer made of any one of aluminum, gold, silver, tungsten, and copper on the black resist layer by a lift-off method.

13. A method for manufacturing a plasmonics infrared wavelength-selective absorber, comprising: forming an infrared absorbing resin layer on a silicon wafer as an infrared absorber, in which black carbon is dispersed in acrylic resin; forming a metal layer on the infrared absorbing resin layer by sputtering or vapor-depositing any one of aluminum, gold, silver, tungsten, and copper; and forming a plasmonics wavelength-selective layer on the metal layer by applying photolithography and etching so as to transmit infrared light of a certain wavelength.

14. The method for producing a plasmonics infrared wavelength-selective absorber according to any one of claims 11 to 13, further comprising forming a plurality of plasmonics wavelength-selective layers, each of which transmits infrared rays of different wavelengths, on the silicon wafer.

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