JP2009204381A - Fabry-perot interferometer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a Fabry-Perot interferometer for efficiently transmitting a light even if the light has a wide wavelength band. <P>SOLUTION: A plurality of projections and recesses 1c are entirely provided in a portion on the other surface 1b of a semiconductor substrate 1. When the portion of an aperture 14 is projected to the other surface 1b in the direction perpendicular to the other surface 1b of the semiconductor substrate 1, the light is transmitted through it. Since an refractive index can be smoothly and continuously changed in an interface between the other surface 1b of the semiconductor substrate 1 and the air, the light can be transmitted efficiently through the interface even if the light has the wide wavelength band. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a Fabry-Perot interferometer provided with an optical multilayer mirror provided with an air gap between a lower mirror and an upper mirror made of a refractive material.

  Conventionally, an apparatus using a Fabry-Perot interferometer in which an optical multilayer film is used to form a high-reflection mirror is known as a gas concentration measurement apparatus, and an optical multilayer film is used to make a high-reflection mirror. An interferometer is proposed in US Pat.

  Specifically, in Patent Document 1, a structure in which a lower mirror and an upper mirror are provided and the lower mirror and the upper mirror are opposed to each other through an air gap is formed on the surface of the substrate. The side mirror is formed by alternately laminating the silicon oxide film and the polycrystalline silicon layer on the substrate, and the upper mirror is formed by alternately laminating the silicon layer and the oxide layer. A Fabry-Perot interferometer having a high-reflection mirror using an optical multilayer film has been proposed.

  In such a Fabry-Perot interferometer, a metal layer is formed integrally with the interferometer structure, and this metal layer prevents radiation transmission (light transmission) outside the optically active central region, called an aperture. A hole is provided. Examples of the material for realizing the aperture include metal, doped silicon, and the like. That is, the light that has been multiple-reflected by the upper and lower mirrors passes through this aperture and is detected by the detector.

  In addition, a layer for forming a cutoff filter element is provided on the back surface of the substrate. In order to prevent light from being reflected at the interface between this layer and the substrate, that is, to transmit light efficiently. A film called an antireflection film is provided on the back surface of the substrate. For example, when the refractive index of the antireflection film to be added is n and the transmission wavelength is λ, nλ≈¼.

  However, in the above-described conventional technique, when a high reflection mirror is configured using an optical multilayer film, the optical multilayer film has a large wavelength dependency of reflectivity, and thus the high reflection band of the mirror is narrowed. Since the spectral band of the Fabry-Perot interferometer corresponds to the high reflection region of the mirror, the Fabry-Perot interferometer formed by a mirror having a narrow high reflection band has a problem that the spectral band becomes narrow. For example, when the wavelength of the high reflection band of the mirror is 3 to 9 μm, the band ΔW is 6 μm or more, and the n ratio is required to be about 3.3 or more.

  Therefore, in Japanese Patent Application No. 2006-319779, the applicant has disclosed materials such as Ge (refractive index = 4) and Si (refractive index = 3.45) that are materials that can be used in semiconductor processes and are transparent to wavelengths of 3 to 9 μm. By combining a high refractive index material with a low refractive index material such as air (refractive index = 1) or vacuum, a high reflection band capable of obtaining a high n ratio (for example, an n ratio of 3.4 or more) is obtained. A wide optical multilayer mirror was proposed. A Fabry-Perot interferometer having this optical multilayer mirror is shown in FIG.

  In FIG. 9, a lower mirror M1 is disposed on a semiconductor substrate 1 made of, for example, a silicon substrate, and is disposed from the lower mirror M1 through an air gap Ag at a position corresponding to the lower mirror M1. An optical multilayer mirror having an upper mirror M2 is shown.

  As shown in FIG. 9, an insulating film 2 made of a silicon oxide film or the like is formed on the entire surface of a semiconductor substrate 1 made of, for example, a silicon substrate. A first high refractive index film 3 having a first refractive index made of polycrystalline silicon or the like is formed on the entire surface of the semiconductor substrate 1 via the insulating film 2.

  A first low refractive index layer 4 having a second refractive index lower than the first refractive index composed of, for example, an air layer is formed in a region of the first high refractive index film 3 to be an optical laminated film mirror. Yes. Then, on the surface of the first high refractive index film 3 including the first low refractive index layer 4, a second high refractive index film 5 having a first refractive index made of, for example, polycrystalline silicon is laminated. Has been. That is, the first low refractive index layer 4 is sandwiched between the first high refractive index film 3 and the second high refractive index film 5.

  The first low refractive index layer 4 has a structure in which the upper surface is covered with the second high refractive index film 5 and the side surfaces are surrounded. Of the second high refractive index film 5, the portion 5 a surrounding the side surface of the first low refractive index layer 4 functions as a reinforcing portion of the first low refractive index layer 4, and the mechanical strength is insufficient. The deformation of the low refractive index layer 4 is suppressed. Specifically, the first low refractive index layer 4 is divided so as to be subdivided into a plurality of pieces, and each of the divided upper surfaces has a hexagonal shape, and the plurality of first low refractive index layers 4 are divided. Are arranged in a honeycomb shape. That is, a hexagonal frustum-shaped space is formed by the portion 5a surrounding the upper surface and the side surface of the first low refractive index layer 4 in the second high refractive index film 5 and the first high refractive index film 3, and this space is formed in the space. The first low refractive index layer 4 is used. A portion 5 a located on the side surface of the hexagonal frustum of the second high refractive index film 5 serves as a reinforcing portion of the first low refractive index layer 4.

  The lower mirror M1 is constituted by the first and second high refractive index films 3 and 5 and the first low refractive index layer 4, and the first low refractive index layer in the second high refractive index film 5. The light is transmitted through the portion located on the upper surface of the light source 4, and the light is not transmitted through the portion 5a of the second high refractive index film 5 located on the side surface of the first low refractive index layer 4 (not so much transmitted). ing.

  The second high-refractive index film 5 and the first high-refractive index film 3 are provided with a wiring layer made of a diffusion layer doped with an impurity (not shown), and an electrode for the lower mirror M1 (hereinafter referred to as a lower part). The potential of the second high refractive index film 5 and the first high refractive index film 3 can be adjusted by applying a voltage to the electrode 11 (referred to as an electrode) through this wiring layer.

  Further, an insulating film 6 made of, for example, a silicon oxide film is formed on the upper surface of the second high refractive index film 5 so as to avoid the lower mirror M1 and its periphery. Then, the third high refractive index film 7 and the fourth high refractive index film 9 having the first refractive index are formed over almost the entire area up to the surface of the insulating film 6 and the position facing the lower mirror M1 and its periphery. In addition, a second low refractive index layer 8 having a second refractive index is formed at the center position. Among these, a region that is not the surface of the insulating film 6, that is, a position facing the lower mirror M1 and its periphery is the membrane Men. Note that the membrane Men is actually wider than the cross-sectional view shown in FIG. 1, and the optical multilayer mirror composed of the lower mirror M1 and the upper mirror M2 is only in a partial region of the membrane Men. Although it is formed, in FIG. 9, the scale is changed for convenience.

  Specifically, a second low-refractive index layer 8 made of, for example, an air layer is formed in a region of the third high-refractive index film 7 to be an optical laminated film mirror. A fourth high refractive index film 9 made of, for example, polycrystalline silicon is laminated on the surface of the third high refractive index film 7 including the second low refractive index layer 8. That is, the second low refractive index layer 8 is sandwiched between the third high refractive index film 7 and the fourth high refractive index film 9.

  The second low refractive index layer 8 has a structure in which the upper surface is covered with the fourth high refractive index film 9 and the side surfaces are surrounded. Of the fourth high-refractive index film 9, the portion 9a surrounding the side surface of the second low-refractive index layer 8 functions as a reinforcing part of the second low-refractive index layer 8, and the second is insufficient in mechanical strength. The deformation of the low refractive index layer 8 is suppressed. Specifically, in the case of the present embodiment, the second low refractive index layer 8 is divided so as to be subdivided into a plurality of parts, and each of the divided upper surfaces has a hexagonal shape, and a plurality of second 2 Low refractive index layers 8 are arranged in a honeycomb (honeycomb) shape. That is, a hexagonal frustum-shaped space is formed by the portion 9a surrounding the upper surface and the side surface of the second low refractive index layer 8 and the third high refractive index film 7 in the fourth high refractive index film 9, and this space is formed in the space. The second low refractive index layer 8 is used. A portion 9 a located on the side surface of the hexagonal frustum of the fourth high refractive index film 9 serves as a reinforcing portion of the second low refractive index layer 8.

  The upper mirror M2 is constituted by the third and fourth high refractive index films 7 and 9 and the second low refractive index layer 8, and the second low refractive index layer 8 of the fourth high refractive index film 9 is formed. The light is transmitted through a portion located on the upper surface of the second high-refractive index film 9 and light is not transmitted (not transmitted so much) through the portion 9a located on the side surface of the second low-refractive index layer 8 in the fourth high-refractive index film 9. Yes.

The upper mirror M2 configured as described above has the same upper surface layout as that of the lower mirror M1.
That is, the honeycomb-shaped top layout of the second low-refractive index layer 8 and the fourth high-refractive index film 9 is the same as the honeycomb-shaped top layout of the first low-refractive index layer 4 and the second high-refractive index film 5. ing. Thereby, the light that has passed through the portion serving as the mirror of the upper mirror M2 can be efficiently incident on the portion serving as the mirror of the lower mirror M1.

  The fourth high-refractive index film 9 and the third high-refractive index film 7 are provided with a wiring layer made of a diffusion layer doped with an impurity (not shown), and an electrode for the upper mirror M2 (hereinafter referred to as an upper electrode). The potential of the fourth high refractive index film 9 and the third high refractive index film 7 can be adjusted by applying a voltage to 12 through this wiring layer.

  Furthermore, an opening 10 reaching the second high refractive index film 5 is formed in the insulating film 6 and the third and fourth high refractive index films 7 and 9 at positions on the outer periphery of the membrane Men. A lower electrode 11 made of Au / Cr or the like is formed in the opening 10 and is brought into ohmic contact with a wiring portion (not shown) made of an impurity diffusion layer formed in the second high refractive index film 5. Yes. Similarly, an upper electrode 12 made of Au / Cr or the like is formed on the surface of the fourth high-refractive index film 9 on the outer periphery of the membrane Men. It is in ohmic contact with a wiring portion (not shown) made of the formed impurity diffusion layer. The wiring portions formed on the second high refractive index film 5 and the fourth high refractive index film 9 are the reinforcing portions of the outer periphery of the lower mirror M1 and the upper mirror M2, the lower mirror M1, and the upper mirror M2. It is preferable that a portion that does not function as a high reflection mirror, such as a portion to be formed, is doped with impurities. This is because light is absorbed when the impurity is doped, and it is preferable that the impurity is not introduced into the portion serving as a mirror.

  A hole 13 is formed inside the membrane Men so as to pass through the third and fourth high-refractive-index films 7 and 9 and connect the air gap Ag and the outside. A hole is formed in part of the high refractive index film 5 on the first low refractive index layer 4 and part of the high refractive index film on the second low refractive index layer 4 of the upper mirror M2. Yes.

  According to this, for example, a fabric having an optical multilayer film mirror having a wide high reflection band compared to the prior art by combining a high refractive index material such as Ge / Air / Ge and Si / Air / Si and a low refractive index material. It becomes possible to use a Perot interferometer.

Also in the Fabry-Perot interferometer using the optical multilayer film mirror as described above and capable of performing spectroscopy in a wide band (n ratio 3.3 or more, ΔW 6 μm or more), an antireflection film for transmitting light on the back surface of the substrate. is required. For this reason, as described above, an antireflection film having a thickness matching the wavelength is provided on the back surface of the substrate.
Japanese Patent No. 3457373

  However, the antireflection film functions as an antireflection film in a narrow wavelength range where ΔW is several μm, but has a wide wavelength band (ΔW is, for example, 6 μm or more) that functions as a sensor necessary for superior gas concentration measurement. When trying to measure, there is a problem that the transmission efficiency is significantly lowered at a wavelength away from the design wavelength of the antireflection film, and it does not function as an antireflection film.

  FIG. 10 is a diagram showing the reflection characteristics of a silicon nitride film having a thickness of 440 nm and a refractive index n of 2 as an antireflection film. As shown in this figure, when the wavelength λ is 4 to 5 μm and the wavelength band is 1 μm, the reflectance of the nitride film is low, and it functions as an antireflection film with high transmission efficiency. On the other hand, when the wavelength λ is smaller than 4 to 5 μm or vice versa, the reflectivity increases accordingly, and the transmission efficiency is lowered. In this case, in order to obtain a low reflectance, the thickness of the nitride film must be reduced or increased depending on the wavelength, but the wavelength band that functions as an antireflection film is about 1 μm, so the target wavelength Otherwise, the transmission efficiency of the antireflection film is lowered.

  An object of the present invention is to provide a Fabry-Perot interferometer that can efficiently transmit light even in a wide wavelength band.

  In order to achieve the above object, according to the first aspect of the present invention, a high refractive index material / low refractive index material / high refractive index material using a high refractive material and a low refractive material on one surface (1a) of the substrate (1). A lower mirror (M1) formed of a three-layer structure of refractive index material is disposed, and an air gap (Ag) from the lower mirror (M1) at a position corresponding to the lower mirror (M1). And an upper mirror (M2) formed of a three-layer structure of a high refractive index material / a low refractive index material / a high refractive index material using a high refractive index material and a low refractive index material. In a Fabry-Perot interferometer equipped with a multilayer mirror, the high refractive index material is silicon or germanium, the low refractive index material is air, and the substrate (1) has a direction perpendicular to the one surface (1a). Project an optical multilayer mirror on the substrate (1) When the portion corresponding to the optical multilayer mirror is allowed to pass light, the portion other than the optical multilayer mirror is provided with an aperture (14) that prevents the passage of light, and the other surface of the substrate (1) ( In 1b), when a portion of the aperture (14) that transmits light in the direction perpendicular to the other surface (1b) is projected onto the other surface (1b), the light is transmitted over the entire portion of the portion that transmits light. A plurality of concaves and convexes (1c) having a sharp shape, which are arranged at a distance interval shorter than the wavelength of light to be generated and whose surface side is thinner than the inside, are provided.

  By utilizing such unevenness (1c), reflection at the interface usually caused by the difference in refractive index between the substrate (1) and air is reduced between the other surface (1b) of the substrate (1) and air. The refractive index can be gradually and continuously changed at the interface. Therefore, even light in a wide wavelength band can be prevented from being reflected at the interface between the substrate (1) and air, and an antireflection function can be provided at an extremely wide wavelength.

  In the invention according to claim 2, each of the plurality of irregularities (1c) is a quadrangular pyramid, the bottom surface of the quadrangular pyramid is arranged on the other surface (1b), and the length of the diagonal line of the bottom surface of the quadrangular pyramid is light. It is characterized by being shorter than the wavelength.

  Thus, the unevenness | corrugation (1c) is a square pyramid, and the refractive index of a board | substrate (1) and air can be gently changed with the side surface of a square pyramid. Further, by defining the length of the diagonal line of the bottom surface of the quadrangular pyramid, it is possible to prevent light from being scattered by the unevenness (1c).

  In the invention described in claim 3, the substrate (1) is a silicon or germanium substrate, the substrate surface is a (100) surface, and the side surfaces of the plurality of irregularities (1c) are (111) surfaces. It is characterized by. By using such a substrate, mid-infrared light can be transmitted and a quadrangular pyramid can be easily formed.

  According to a fourth aspect of the present invention, the aperture (14) is provided on the other surface (1b) of the substrate (1) and is formed of a metal film that absorbs light.

  As a result, only the light that has been multiple-reflected by the optical multilayer mirror can be taken out from the portion of the aperture (14) through which the light passes. That is, it is possible to prevent noise light in the substrate (1) from being taken out from the aperture (14).

  As in the invention described in claim 5, the light reflecting surface of the optical multilayer mirror is subdivided into hexagons, and the subdivided optical multilayer mirror is arranged in a honeycomb shape so that the other side of the substrate (1) is arranged. Unevenness (1c) can be provided in the entire region of the surface (1b) where the hexagonal optical multilayer mirror disposed in a honeycomb shape is projected in a direction perpendicular to the other surface (1b).

  In this case, as in the invention described in claim 6, the area of one hexagon projected on the other surface (1b) of the substrate (1) is one hexagon of the subdivided optical multilayer mirror. It is preferable that it is smaller than the area. Thereby, even if the noise light enters the substrate (1) slightly obliquely, it can be prevented from entering.

  In addition, the code | symbol in the bracket | parenthesis of each said means shows the correspondence with the specific means as described in embodiment mentioned later.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following embodiments, the same or equivalent parts are denoted by the same reference numerals in the drawings.

(First embodiment)
Hereinafter, a first embodiment of the present invention will be described with reference to the drawings. In the following, the same components as those shown in FIG. 9 are denoted by the same reference numerals. The Fabry-Perot interferometer shown in this embodiment is used, for example, in an apparatus for measuring a gas concentration.

  FIG. 1 is a plan view of a Fabry-Perot interferometer according to the first embodiment of the present invention, in which (a) shows a front side, that is, a surface on which light enters the interferometer, and (b) shows a back side, The surface from which light is emitted from the interferometer is shown. Moreover, FIG. 2 is AA sectional drawing of Fig.1 (a). The Fabry-Perot interferometer will be described below with reference to FIGS.

  As shown in FIG. 2, the Fabry-Perot interferometer includes a semiconductor substrate 1 made of, for example, a silicon substrate, an optical multilayer mirror provided on one surface 1 a of the semiconductor substrate 1, and the other surface of the semiconductor substrate 1. The aperture 14 and the coating layer 15 provided in 1b are provided.

  The optical multilayer mirror has the same structure as that shown in FIG. Here, as the high refractive index material constituting each of the mirrors M1 and M2, a material formed of silicon or germanium is employed. The crystal plane of the semiconductor substrate 1 is a (100) plane.

  Further, as shown in FIG. 1A, light is incident on a transmissive region where the upper mirror M2 is provided in the region of the membrane Men.

  When the optical multilayer mirror is projected onto the semiconductor substrate 1 in a direction perpendicular to the one surface 1a of the semiconductor substrate 1, the aperture 14 allows light to pass through a portion corresponding to the optical multilayer mirror and removes the optical multilayer mirror. This part prevents the passage of light. That is, it has a through hole through which light passes.

  Therefore, a portion of the aperture 14 through which light passes is open, and the other surface 1b of the semiconductor substrate 1 is exposed. On the other hand, the portion of the aperture 14 that does not transmit light covers the other surface 1 b of the semiconductor substrate 1. According to this, it becomes possible to take out only the light multiple-reflected by the optical multilayer mirror from the portion of the aperture 14 through which light passes, so that noise light in the semiconductor substrate 1 is not taken out from the aperture 14 to the outside. become.

  As shown in FIG. 1B, in the present embodiment, the aperture 14 has one through hole through which light passes. Such an aperture 14 is formed of a metal film that absorbs light. For example, a material such as TiW is used as the metal film.

  The covering layer 15 is formed on the aperture 14 and protects the aperture 14. As such a covering layer 15, for example, a SiN film is employed.

  Further, as shown in FIGS. 1B and 2, the other surface 1b of the semiconductor substrate 1 has a portion that transmits light in the aperture 14 in the direction perpendicular to the other surface 1b. A plurality of minute irregularities 1c are provided in a portion that transmits the light, that is, the entire light transmission region.

  In the present embodiment, since the aperture 14 is provided on the other surface 1b of the semiconductor substrate 1, the entire other surface 1b of the semiconductor substrate 1 exposed from the opening portion of the aperture 14 has an uneven shape 1c.

  Each of the plurality of irregularities 1c is a quadrangular pyramid, and the bottom surface of the quadrangular pyramid is disposed on the other surface 1b. Such a pattern of the other surface 1b of the semiconductor substrate 1 uses a (100) plane as the crystal plane of the semiconductor substrate 1 and utilizes anisotropic etching of silicon, thereby forming a plurality of patterns formed in the transmission region. The irregularities 1c each have a quadrangular pyramid shape. Since the other surface 1b of the semiconductor substrate 1 is the (100) plane, the side surface of the quadrangular pyramid is the (111) plane.

  The minute irregularities 1c are arranged at a distance interval shorter than the wavelength of light to be transmitted and have a pointed shape whose surface side is narrower than the inside, so that the light that has passed through the semiconductor substrate 1 passes through the semiconductor substrate. It plays a role of smoothly and continuously changing the refractive index at the interface between 1 and air. As a result, the refractive index at the interface between the semiconductor substrate 1 and air gently changes, so that the light that has passed through the semiconductor substrate 1 is a difference in refractive index at the interface between the other surface 1b of the semiconductor substrate 1 and the air. The light is emitted from the other surface 1b without being reflected. In particular, at a wavelength longer than the distance interval of minute irregularities, the refractive index functions to change gently, and thus functions as an antireflection for broadband light.

  “Fine unevenness 1c” means that the length of the diagonal line of the bottom surface of the quadrangular pyramid is shorter than the wavelength of light, and is preferably shorter than half the wavelength. However, if the length of the diagonal line is too short, the height of the quadrangular pyramid is lowered, so the change in refractive index does not become gradual, and the transmittance of light passing through the unevenness 1c, that is, the antireflection performance is Getting worse.

  Therefore, in this embodiment, specifically, in order to disperse the band 3 to 9 μm (ΔW6 μm), the minute unevenness and the length are measured in the in-plane dimension (diagonal line of the bottom surface of the quadrangular pyramid) at the minimum wavelength. It was set to 2 μm, which is 3 μm or less. At that time, the height is determined by the shape of a quadrangular pyramid and is formed as half the length of the diagonal line.

  On the other hand, the semiconductor substrate 1 is made of silicon or germanium having transmission characteristics from near infrared light to mid infrared light. At this time, the germanium substrate is suitable for the semiconductor substrate 1 because it has a transmission characteristic up to a long wavelength, while infrared light is easily absorbed by the impurities contained in the semiconductor substrate 1. > 1000 Ωcm) is preferred.

  Next, a manufacturing method of the Fabry-Perot interferometer shown in FIGS. 1 and 2 will be described with reference to manufacturing steps of the Fabry-Perot interferometer shown in FIGS.

[Step shown in FIG. 3 (a)]
First, a semiconductor substrate 1 composed of a silicon substrate or the like is prepared. At this time, the use of the (100) substrate is advantageous for forming the minute unevenness 1c later. Then, an insulating film 2 made of, for example, a silicon oxide film and a first high refractive index film 3 made of polycrystalline silicon or the like are deposited on the entire surface of the semiconductor substrate 1, and the first high refractive index film 3 is formed. A sacrificial film 20 made of a material having a high etching selectivity with the first and second high refractive index films 3 and 5 such as a silicon oxide film is deposited on the entire surface. At this time, the thickness of the sacrificial film 20 is equivalent to the thickness of the first low refractive index layer 4 described above. Thereafter, after a resist 21 is disposed on the surface of the sacrificial film 20, an opening 21a is formed so as to leave only a portion corresponding to a position where the first low refractive index layer 4 is to be formed in the resist 21, and etching is performed in this state. By performing (isotropic etching or the like), the sacrificial film 20 is formed into a hexagonal frustum shape. Thereafter, the resist 21 is removed.

[Step shown in FIG. 3B]
The second high refractive index film 5 made of polycrystalline silicon or the like is deposited on the entire surface of the portion of the sacrificial film 20 and the first high refractive index film 3 that is not covered with the sacrificial film 20. At this time, since the sacrificial film 20 has a hexagonal frustum shape, the portion of the second high refractive index film 5 disposed on the sacrificial film 20 is inherited, and the hexagonal frustum shape is obtained. It becomes.

  Subsequently, after disposing the resist 22 on the surface of the second high refractive index film 5, an opening 22a is formed in a portion of the resist 22 corresponding to the hole M1b of the lower mirror M1 in a different cross section from FIG. Is provided. Then, the hole M1b is opened by performing dry etching (anisotropic etching) using the resist 22 as a mask. At this time, since the shape of the second high refractive index film 5 inherits the hexagonal frustum shape, when the hole M1b is formed, the boundary portion between the first high refractive index film 3 and the sacrificial film 20 Residues are less likely to occur in the vicinity.

  Thereafter, after removing the resist 22, impurities are ion-implanted using a mask (not shown) having an opening in the wiring portion formation region.

[Step shown in FIG. 3 (c)]
An insulating film 6 made of, for example, a silicon oxide film is deposited on the entire surface of the second high refractive index film 5. At this time, the film thickness of the insulating film 6 is the size of the air gap Ag, that is, the thickness corresponding to the interval between the lower mirror M1 and the upper mirror M2. The material of the insulating film 6 is not particularly limited, but is preferably the same as the material of the sacrificial film 20. Depending on the thickness of the insulating film 6, the uneven shape of the second high refractive index film 5 remains on the surface of the insulating film 6, but may remain.

[Step shown in FIG. 3 (d)]
A third high-refractive index film 7 made of, for example, polycrystalline silicon is deposited on the entire surface of the insulating film 6, and third and fourth high-index films such as a silicon oxide film are deposited on the entire surface of the second high-refractive index film 7. A sacrificial film 23 made of a material having a high etching selectivity with respect to the refractive index films 7 and 9 is deposited. At this time, the thickness of the sacrificial film 23 is equivalent to the thickness of the second low refractive index layer 8 described above. Thereafter, after a resist 24 is disposed on the surface of the sacrificial film 23, an opening 24a is formed so as to leave only a portion of the resist 24 corresponding to a position where the second low refractive index layer 8 is to be formed, and etching is performed in this state. By performing (isotropic etching or the like), the sacrificial film 23 is formed into a hexagonal frustum shape. Thereafter, the resist 24 is removed.

[Step shown in FIG. 3 (e)]
A fourth high refractive index film 9 made of polycrystalline silicon or the like is deposited on the entire surface of the portion of the sacrificial film 23 and the third high refractive index film 7 that is not covered with the sacrificial film 23. At this time, since the sacrificial film 23 has a hexagonal frustum shape, the shape of the portion of the fourth high refractive index film 9 disposed on the sacrificial film 23 is inherited, and the hexagonal frustum shape is obtained. It becomes.

  Subsequently, impurities are ion-implanted using a mask (not shown) having an opening in the wiring portion formation region, and then the mask is removed.

  Further, after the resist 25 is disposed on the surface of the fourth high refractive index film 9, an opening 25a (a different cross section from FIG. 3E) and an opening are formed in the resist 25 corresponding to the hole M2b of the upper mirror M2. An opening 25 b is provided in a portion corresponding to the portion 10 and the hole 13. Then, by performing dry etching (anisotropic etching) using the resist 25 as a mask, the hole M2b and the hole 13 are opened, and a part of the opening 10 is formed.

[Step shown in FIG. 4 (a)]
Subsequently, after removing the resist 25, the fourth high refractive index film 9 is used as a mask and etching is performed by wet with HF or the like. As a result, the insulating film 6 is partially removed to form the opening 10. At this time, the insulating film 6 may be prevented from being removed through the hole M2b and the hole 13 by performing etching in a state where the mask is disposed in the portion where the membrane Men is located in the fourth high refractive index film 9. However, if it is removed, it becomes easier to remove the insulating film 6 below the membrane Men in order to form the membrane Men.

  Thereafter, the mask used to cover the opening 10 is removed, and then Au / Cr is vapor-deposited using a metal mask or the like to form a lower electrode 11 in the opening 10 and an upper portion on the outer periphery of the membrane Men. Electrodes 12 are formed and ground and polished as necessary.

[Step shown in FIG. 4B]
Subsequently, a metal TiW serving as the aperture 14 is formed on the back surface, and is patterned and etched so as to remain in a region other than the transmission region.

  Thereafter, in order to form minute unevenness 1c in the transmission region, a SiN film (silicon nitride) is formed by plasma CVD and patterned. Thereby, the coating layer 15 is formed on the aperture 14.

[Step shown in FIG. 4 (c)]
Next, using a dedicated jig, the SiN film serving as the coating layer 15 is used as a mask, and only a back surface (the other surface 1b of the semiconductor substrate 1) is exposed to a strong alkaline solution (KOH, TMAH) or the like, so that different silicon is used. By performing isotropic etching, a plurality of quadrangular pyramid-shaped irregularities 1 c are formed in the transmission region. Since all the surfaces of the silicon exposed to the strong alkali solution are patterned so as to stop at the (111) plane, the structure can be formed stably.

  At this time, the SiN film used as the mask for the transmissive region part is naturally peeled off when the unevenness 1c is formed.

  In this embodiment, anisotropic silicon etching using a strong alkaline solution is used as a method for forming the unevenness 1c. However, the present invention is not limited to this, and the distance is shorter than the wavelength of light to be transmitted. Any method can be used as long as it can be arranged and can form a pointed shape whose surface is thinner than the inside.

[Step shown in FIG. 4 (d)]
Next, the insulating film 6 and the first and second low-refractive index layers 4 and 8 are disposed through the hole M2b of the upper mirror M2 and the hole 13 located on the outer periphery thereof, and further through the hole 1b of the lower mirror M1. The sacrificial films 20 and 23 existing in the space to be formed are etched. At this time, the insulating film 6 exposed in the opening 10 may be prevented from being removed by covering the opening 10 with a mask (not shown) as necessary. By this etching, a portion of the insulating film 6 located under the membrane Men is removed, whereby an air gap Ag is formed and the first and second low refractive index layers 4 and 8 are formed.

  By such a manufacturing method, a Fabry-Perot interferometer having the optical multilayer mirror of the present embodiment shown in FIGS. 1 and 2 is completed.

  Gas concentration detection using the Fabry-Perot interferometer manufactured as described above is performed as follows. First, a light source, a gas introduction cell, a bandpass filter, a Fabry-Perot interferometer, and a detector are arranged in a straight line in this order. In the Fabry-Perot interferometer, the optical multilayer mirror side is directed to the bandpass filter side, and the minute unevenness 1c side is directed to the detector side. The optical multilayer mirror of the Fabry-Perot interferometer is arranged so that light is incident vertically.

  When the gas introduction cell is filled with gas and light is emitted from the light source, the light passes through the gas and bandpass filter and enters the optical multilayer mirror of the Fabry-Perot interferometer. The light that has entered the optical multilayer mirror enters the semiconductor substrate 1 by being multiple-reflected between the upper mirror M2 and the lower mirror M1, and is fabricated through the open portion of the aperture 14, that is, through the minute unevenness 1c. The light is emitted from the Perot interferometer and received by the detector.

  Here, the voltage applied to the upper electrode 12 and the lower electrode 11 of the Fabry-Perot interferometer is changed to adjust the distance between the upper mirror M2 and the lower mirror M1, thereby spectroscopically analyzing the light incident on the optical multilayer mirror. can do. Therefore, the component of the gas contained in the gas can be examined by spectroscopically analyzing the light incident on the optical multilayer mirror to 3 to 9 μm and measuring the absorption spectrum of the gas in the gas introduction cell.

  FIG. 5 is a diagram showing a comparison of the antireflection ability between the semiconductor substrate 1 having the uneven surface 1b formed on the other surface 1b and the semiconductor substrate 1 shown in FIG. As shown in this figure, in the Fabry-Perot interferometer according to this embodiment, the reflectance hardly changes depending on the wavelength even in a wide wavelength band of 2 to 10 μm. That is, it can be said that even in a wide wavelength band, low reflectance can be maintained and light can be transmitted efficiently.

  This is because when the light that has entered the semiconductor substrate 1 from the optical multilayer mirror is emitted into the air through the aperture 14, the refractive index of the semiconductor substrate 1 and air changes smoothly and continuously. This is because there is no reflection caused by the rate difference.

  As described above, in the present embodiment, when the portion of the aperture 14 that transmits light in the direction perpendicular to the other surface 1b is projected onto the other surface 1b of the semiconductor substrate 1, A feature is that a plurality of concaves and convexes 1c are provided over the entire portion of the light transmitting portion.

  The minute irregularities 1c are arranged at a distance interval shorter than the wavelength of light to be transmitted and have a pointed shape whose surface side is narrower than the inside, so that the light that has passed through the semiconductor substrate 1 passes through the semiconductor substrate. It plays a role of smoothly and continuously changing the refractive index at the interface between 1 and air.

  Thereby, even if it is light of a wide wavelength band, light can be efficiently permeate | transmitted at the interface of the semiconductor substrate 1 and air.

  Moreover, the refractive index of the semiconductor substrate 1 and air can be gently changed easily by making the unevenness | corrugation 1c into a square pyramid. Furthermore, by making the length of the diagonal line of the bottom surface of the quadrangular pyramid shorter than the wavelength of light, it is possible to prevent light from being scattered by the unevenness 1c and to prevent the light transmittance from being lowered.

  Then, by forming the aperture 14 with a metal film that absorbs light, noise light that has entered the semiconductor substrate 1 from the optical multilayer mirror can be absorbed. Thereby, it is possible to extract light with high accuracy from the Fabry-Perot interferometer.

(Second Embodiment)
In the present embodiment, only different parts from the first embodiment will be described. In the first embodiment, the aperture 14 is provided with only one through-hole through which light passes. However, in this embodiment, the through-hole corresponding to each hexagon of the subdivided optical multilayer film mirror is provided. It is characterized by being provided in the aperture 14.

  6A is a plan view of the other surface 1b of the semiconductor substrate 1 in the Fabry-Perot interferometer according to the present embodiment, and FIG. 6B is an enlarged view of a portion B in FIG. 6A. FIG. 7 is a cross-sectional view of the Fabry-Perot interferometer according to the present embodiment, and is a cross-sectional view corresponding to the AA cross section of FIG.

  As shown in FIG. 7, the light reflection surface of the optical multilayer mirror is subdivided into hexagons, and the subdivided optical multilayer mirrors are arranged in a honeycomb shape. Furthermore, an aperture 14 having an opening is provided in a region of the other surface 1b of the semiconductor substrate 1 where a hexagonal optical multilayer mirror disposed in a honeycomb shape in a direction perpendicular to the other surface 1b is projected. ing. That is, as shown in FIG. 6A, the aperture 14 is provided with a hexagonal aggregate.

  Specifically, as shown in FIG. 6B, when the hexagonal shape of the optical multilayer mirror is projected onto the aperture 14 in the light traveling direction, the aperture 14 has an opening at a location where the hexagonal shape is projected. Is provided. And the unevenness | corrugation 1c is provided in each opening part of the aperture 14 among the other surfaces 1b of the semiconductor substrate 1. FIG. The unevenness 1c is provided over the entire area of each opening.

  By forming the hexagonal opening in the aperture 14 in this way in a honeycomb shape, light at a portion where the characteristics are slightly deteriorated can be blocked at the edge of the honeycomb mirror (subdivided optical multilayer film mirror). .

  The area of one hexagon projected on the other surface 1b of the semiconductor substrate 1 is smaller than the area of one hexagon of the subdivided optical multilayer film mirror. This is because even if light is incident substantially vertically from the upper part of the semiconductor substrate 1, the light spreads slightly, and the light beam has an angle. Therefore, the light whose characteristics are slightly deteriorated at the honeycomb mirror edge (boundary between the hexagon and other portions) also has an angle when it comes to the back surface (the other surface 1b of the semiconductor substrate 1), and is within the minute unevenness 1c. This is because the noise increases because the light enters.

  Specifically, as a result of forming the minute unevenness 1c in the hexagonal region reduced to 80% of the area of the honeycomb mirror in the aperture 14, almost no light that causes noise was observed. As described above, it is possible to reduce the noise of light passing through the Fabry-Perot interferometer by matching the opening of the aperture 14 with the hexagonal shape of the optical multilayer mirror.

(Third embodiment)
In the present embodiment, only portions different from the first and second embodiments will be described. In the first and second embodiments, as a method for forming the minute unevenness 1c, the (100) plane of the semiconductor substrate is used to form a quadrangular pyramid having the (111) plane. Even if it does not use, the unevenness | corrugation 1c can be formed also by the following methods.

  FIG. 8 is a diagram showing a manufacturing process of the unevenness 1c in the present embodiment. As shown in this figure, a fine mask pattern 30 such as a square or a circle is formed in the transmissive region of the other surface 1b of the semiconductor substrate 1, and dry etching is performed under etching conditions close to isotropic. Thereby, a tapered inclined surface is formed on the other surface 1b.

  In this case, the length in the surface direction of the other surface 1b of the semiconductor substrate 1 can be made shorter than the wavelength in one convex portion of the unevenness 1c, while the depth direction (light traveling direction) of the semiconductor substrate 1 is lengthened. Therefore, the refractive index can be changed more gradually, which is preferable.

(Other embodiments)
In each of the embodiments described above, the aperture 14 is provided on the other surface 1b of the semiconductor substrate 1, but this is an example, and the aperture 14 may be provided at another location.

It is a top view of the Fabry-Perot interferometer which concerns on 1st Embodiment of this invention, (a) is a top view of the surface side of an interferometer, (b) is a top view of the back surface side of an interferometer. It is AA sectional drawing of Fig.1 (a). It is a manufacturing-process figure of the Fabry-Perot interferometer shown in FIG. 1 and FIG. FIG. 4 is a manufacturing process diagram of the Fabry-Perot interferometer following FIG. 3. It is the figure which showed the correlation of a wavelength and a reflectance. (A) is a top view of the other surface of a semiconductor substrate in the Fabry-Perot interferometer concerning 2nd Embodiment of this invention, (b) is the B section enlarged view of (a). It is sectional drawing of the Fabry-Perot interferometer which concerns on 2nd Embodiment. In 3rd Embodiment of this invention, it is the figure which showed the manufacturing process of an unevenness | corrugation. It is sectional drawing of the Fabry-Perot interferometer which has an optical multilayer film mirror. It is the figure which showed the reflective characteristic of the nitride film whose thickness is 440 nm and whose refractive index n is 2 as an antireflection film.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Semiconductor substrate 1a One surface of a semiconductor substrate 1b The other surface of a semiconductor substrate 1c Concavity and convexity 14 Aperture M1 Lower mirror M2 Upper mirror Ag Gap

Claims (6)

A lower mirror (M1) formed of a three-layer structure of a high refractive index material / low refractive index material / high refractive index material using a high refractive index material and a low refractive index material on one surface (1a) of the substrate (1). ) And at a position corresponding to the lower mirror (M1), an air gap (Ag) is disposed from the lower mirror (M1), and a high refractive material and a low refractive material are used. In a Fabry-Perot interferometer including an optical multilayer mirror having an upper mirror (M2) formed of a three-layer structure of high refractive index material / low refractive index material / high refractive index material,
The high refractive index material is silicon or germanium, the low refractive index material is air,
When the optical multilayer mirror is projected onto the substrate (1) in a direction perpendicular to the one surface (1a), light passes through the substrate (1) at a portion corresponding to the optical multilayer mirror. In addition, an aperture (14) that prevents passage of light is provided in a portion excluding the optical multilayer mirror,
On the other surface (1b) of the substrate (1), a portion of the aperture (14) that transmits light in the direction perpendicular to the other surface (1b) is projected onto the other surface (1b). In this case, a plurality of concave and convex portions (1c) having a pointed shape, which is arranged at a distance interval shorter than the wavelength of the light to be transmitted and whose surface side is narrower than the inside, is provided in the entire portion where the light is transmitted. Fabry-Perot interferometer, characterized in that Each of the plurality of irregularities (1c) is a quadrangular pyramid, and a bottom surface of the quadrangular pyramid is disposed on the other surface (1b),
The Fabry-Perot interferometer according to claim 1, wherein a length of a diagonal line on a bottom surface of the quadrangular pyramid is shorter than a wavelength of the light.   The substrate (1) is a silicon or germanium substrate, a substrate surface is a (100) surface, and side surfaces of the plurality of irregularities (1c) are (111) surfaces. Fabry-Perot interferometer described in 1.   The said aperture (14) is provided in the other surface (1b) of the said board | substrate (1), and is formed with the metal film which absorbs light, The any one of Claim 1 thru | or 3 characterized by the above-mentioned. Fabry-Perot interferometer described in 1. Of the optical multilayer mirror, the light reflecting surface is subdivided into hexagons, and the subdivided optical multilayer mirror is arranged in a honeycomb shape,
Of the other surface (1b) of the substrate (1), the irregularities are formed over the entire region where the hexagonal optical multilayer mirror arranged in the honeycomb shape is projected in a direction perpendicular to the other surface (1b). The Fabry-Perot interferometer according to any one of claims 1 to 4, wherein (1c) is provided.   The area of one hexagon projected on the other surface (1b) of the substrate (1) is smaller than the area of one hexagon of the subdivided optical multilayer film mirror. The Fabry-Perot interferometer according to claim 5.

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