Variable wavelength interference filter

Abstract

To provide a variable wavelength interference filter whose size can be reduced and whose diameter can be increased, and which is easily manufactured.SOLUTION: A variable wavelength interference filter comprises: a first substrate provided with a first reflective film; and a second substrate provided with a second reflective film that is opposed to the first reflective film with a gap being interposed. The first substrate is an SOI substrate in which a first layer, a second layer, and a third layer are layered in this order along a thickness direction, and includes: a movable portion provided with the first reflective film; a diaphragm portion that surrounds the movable portion; and a base portion that supports the movable portion through the diaphragm portion so as to be able to advance and retreat along the thickness direction. The diaphragm portion is a portion having a thickness in the thickness direction smaller than the base portion due to a groove opening in a surface of the first substrate, which is on an opposite side of the second substrate, and includes the second layer and the third layer. At least surfaces, on the second substrate side, of the base portion and the diaphragm portion of the first substrate are flat when the movable portion is not displaced.SELECTED DRAWING: Figure 4

Description

Technical Field

[0001] The present invention relates to a wavelength-variable interference filter.

Background Art

[0002] Conventionally, a wavelength-variable interference filter that outputs light of a predetermined wavelength from incident light has been known (for example, Patent Document 1). The wavelength-variable interference filter described in Patent Document 1 includes a first substrate provided with a first mirror, a second substrate provided with a second mirror facing the first mirror with a gap therebetween, a first electrode provided on the first substrate, and a second electrode provided on the second substrate. The movable part and the diaphragm part are formed by forming a resist pattern having an opening at a position corresponding to the diaphragm part of the first substrate and performing wet etching (isotropic etching). Therefore, the diaphragm part has a shape including a flat part corresponding to the mask position, and a first inclined part and a second inclined part formed by over-etching around the flat part.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the above-mentioned Patent Document 1, a first inclined part is formed along the outer periphery of the annular flat part of the diaphragm part by wet etching, and a second inclined part is formed along the inner periphery. Therefore, there is a problem that the movable part becomes smaller as the first inclined part and the second inclined part are provided in the wavelength-variable interference filter. Further, in wet etching, it is difficult to adjust the etching amount, and it is also difficult to control the film thickness so that the thickness of the flat part is uniform, resulting in a decrease in yield and an increase in process load.

Means for Solving the Problems

[0005] The wavelength-variable interference filter according to the first aspect of the present disclosure includes a first substrate provided with a first reflective film, and a second substrate provided with a second reflective film facing the first reflective film through a gap. The first substrate is a SOI substrate having layers in the order of a first layer made of Si, a second layer made of SiO2, and a third layer made of Si along the thickness direction from the first substrate toward the second substrate. The first substrate includes a movable portion where the first reflective film is provided, a diaphragm portion surrounding the movable portion when viewed from the thickness direction from the first substrate toward the second substrate, and a base portion surrounding the diaphragm portion when viewed from the thickness direction and supporting the movable portion so as to be movable forward and backward along the thickness direction through the diaphragm portion. The diaphragm portion is a portion having a thickness thinner than that of the base portion in the thickness direction by a groove opening on the surface of the first substrate opposite to the second substrate, and is composed of the second layer and the third layer. At least the surfaces of the base portion and the diaphragm portion of the first substrate on the second substrate side are flat when the movable portion is not displaced.

Brief Description of the Drawings

[0006]

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Embodiments for Carrying Out the Invention

[0007] [First Embodiment] Hereinafter, the wavelength-variable interference filter according to the first embodiment will be described.

[0008] [Overall Configuration of Wavelength-Variable Interference Filter 1] FIG. 1 is a perspective view showing a schematic configuration of a wavelength-variable interference filter 1 according to the first embodiment. FIG. 2 is a perspective view showing a schematic configuration of a first substrate constituting the wavelength-variable interference filter 1. FIG. 3 is a perspective view showing a schematic configuration of a second substrate constituting the wavelength-variable interference filter 1. FIG. 4 is a cross-sectional view showing a schematic configuration of the wavelength-variable interference filter 1. This wavelength-variable interference filter 1 is a spectroscopic filter capable of changing the transmission wavelength according to a drive voltage input from the outside.

[0009] As shown in FIGS. 1 and 4, the wavelength-variable interference filter 1 of the present embodiment includes a first substrate 2 and a second substrate 3 disposed opposite to each other, a first reflection film 41 provided on the first substrate 2 (see FIG. 4), a second reflection film 42 provided on the second substrate 3 (see FIGS. 3 and 4), and a drive electrode 5 provided on the second substrate (see FIGS. 3 and 4).

[0010] In the following description, the direction from the first substrate 2 to the second substrate 3 is defined as the Z direction, one direction orthogonal to the Z direction is defined as the X direction, and the direction orthogonal to the Z direction and the X direction is defined as the Y direction. The Z direction corresponds to the thickness direction of the wavelength-variable interference filter 1.

[0011] The first substrate 2 and the second substrate 3 are each formed of a material capable of transmitting light. In the present embodiment, the first substrate 2 is a substrate formed by appropriately processing an SOI (Silicon On Insulator) substrate. The second substrate 3 is a substrate formed by appropriately processing a Si substrate. Specifically, the first substrate 2 is configured by appropriately processing an SOI substrate in which a support layer 2A made of Si, a BOX layer 2B (Buried oxide layer) made of SiO2, and an active layer 2C made of Si are sequentially layered along the Z direction. Note that the support layer 2A is the first layer of the present disclosure, the BOX layer 2B is the second layer of the present disclosure, and the active layer 2C is the third layer of the present disclosure. In addition, the first substrate 2 of the present embodiment is composed of a special SOI substrate. That is, the first substrate 2 is an SOI substrate in which the BOX layer 2B is disposed only at a predetermined position, and the other portions are composed of the support layer 2A and the active layer 2C.

[0012] In the present embodiment, the first substrate 2 has a first surface 21 facing the second substrate 3 and a second surface 22 on the side opposite to the first surface 21. When the first substrate 2 is viewed from the Z direction, an annular groove 23 surrounding the first reflection film 41 is formed on the second surface 22 of the first substrate 2. Thereby, the first substrate 2 includes a movable portion 24 which is a portion where the first reflection film 41 is provided, a diaphragm portion 25 surrounding the movable portion 24, and a base portion 26 that supports the movable portion 24 via the diaphragm portion 25 so as to be displaceable in the Z direction.

[0013] Here, the position where the above-described BOX layer 2B is provided is a predetermined margin range centered on the diaphragm portion 25. That is, the BOX layer 2B is disposed in the diaphragm portion 25, in a range from the boundary position with the movable portion 24 to the inside of a predetermined margin, and in a range from the boundary position with the diaphragm portion 25 to the outside of a predetermined margin in the base portion 26. Therefore, most of the center of the movable portion 24 and most of the base portion 26 are configured such that the active layer 2C is laminated on the support layer 2A, that is, they are composed of only Si.

[0014] The diaphragm portion 25 is a portion where the support layer 2A is penetrated by the groove 23 and the surface of the BOX layer 2B is exposed, and is formed to have a thickness in the Z direction thinner than that of the movable portion 24 and the base portion 26. That is, the diaphragm portion 25 is composed of the BOX layer 2B and the active layer 2C. More specifically, as shown in FIG. 4, the groove 23 formed in the first substrate 2 extends annularly so as to surround the movable portion 24 while opening to the second surface 22 which is the surface of the first substrate 2. Here, the width direction of the groove 23 (hereinafter referred to as the groove width direction) is a direction orthogonal to each of the Z direction and the extending direction (circumferential direction) of the groove 23, and is determined for each position in the extending direction of the groove 23. This groove 23 opens to the second surface 22 of the first substrate 2, has side walls 23A along the Z direction, and is configured with the surface of the BOX layer 2B as the bottom surface 23B. That is, the side walls 23A of the groove 23 are perpendicular or substantially perpendicular to the bottom surface 23B. Therefore, from the opening end on the second surface 22 side to the bottom surface 23B of the BOX layer 2B, the width W1 in the groove width direction is uniform. Also, in the present embodiment, the diaphragm portion 25 is composed of a two-layer structure of the BOX layer 2B and the active layer 2C. Therefore, in the wavelength-variable interference filter 1 of the present embodiment, the surface of the first substrate 2 facing the second substrate 3 is composed of the active layer 2C of the SOI substrate, and is flat in a state where the movable portion 24 is not displaced in the Z direction.

[0015] Also, in the first substrate 2 of the present embodiment, the active layer 2C is doped with impurities. Specifically, as the impurities, B (boron) or P (phosphorus) is doped, whereby the conductivity of the active layer 2C is improved, and the active layer 2C of the first substrate 2 functions as an electrode.

[0016] The second substrate 3 is a substrate formed by processing a Si substrate. The first substrate 2 and the second substrate 3 are integrally configured as structures that form a cavity C between them. The second substrate 3 has a third surface 31 facing the first substrate 2 and a fourth surface 32 on the side opposite to the third surface 31. A first recess 33 with a predetermined depth is formed at the central portion of the third surface 31 of the second substrate 3, and the cavity C between the first substrate 2 and the second substrate 3 is formed by the first recess 33. Further, a reflective film installation portion 34 is formed in the first recess 33. For example, in the present embodiment, the reflective film installation portion 34 is a concave groove portion with a predetermined depth provided on the bottom surface of the first recess 33. Note that the reflective film installation portion 34 is set according to the initial gap between the first reflective film 41 and the second reflective film 42, that is, the wavelength of the light transmitted through the wavelength-variable interference filter 1 in a state where the movable portion 24 is not displaced in the Z direction. Therefore, the depth of the concave groove portion as the reflective film installation portion 34 may be appropriately set according to the initial gap. For example, when the initial gap is made smaller, the depth of the concave groove portion is made smaller, and in some cases, the reflective film installation portion 34 may be flush with the bottom surface of the first recess 33. Further, when the initial gap is made smaller, the reflective film installation portion 34 may be configured as a pedestal protruding from the bottom surface of the first recess 33 toward the first substrate 2 side.

[0017] An insulating layer 35 is laminated on the third surface 31 of the second substrate 3 of the present embodiment, that is, on the first recess 33 facing the first substrate 2 and the reflective film installation portion 34, respectively.

[0018] The first reflective film 41 is provided on the movable portion 24 of the first substrate 2, and the second reflective film 42 is provided on the reflective film installation portion 34 of the second substrate 3. The first reflective film 41 and the second reflective film 42 face each other with a gap G therebetween. The dimension of this gap G corresponds to the wavelength of the light transmitted through the wavelength-variable interference filter 1. When the wavelength-variable interference filter 1 is viewed from the Z direction, the region where the first reflective film 41 and the second reflective film 42 face each other becomes the filter region of the wavelength-variable interference filter 1.

[0019] In this embodiment, an SOI substrate is used as the first substrate 2, and an Si substrate is used as the second substrate 3, and light of a desired wavelength is transmitted for light in the near-infrared to infrared region. Therefore, as the first reflective film 41 and the second reflective film 42, a film material having reflection characteristics with respect to the target light wavelength range is used. Specifically, as the first reflective film 41 and the second reflective film 42, a dielectric multilayer film formed by alternately laminating Si and SiO2 is used.

[0020] By the way, in this embodiment, the first substrate 2 is manufactured by processing a special SOI substrate, so that the BOX layer 2B is not provided at the position where the first reflective film 41 of the movable part 24 is provided. For this reason, in this embodiment, in the filter region, there is no boundary between the BOX layer 2B and the support layer 2A, and no boundary between the BOX layer 2B and the active layer 2C, and light is not reflected by these boundaries.

[0021] FIG. 5 is a diagram showing the spectral spectrum (transmission spectrum) of the wavelength-variable interference filter 1 in this embodiment and the spectral spectrum (transmission spectrum) of the wavelength-variable interference filter of the comparative example. Here, the wavelength-variable interference filter of the comparative example is formed by using a normal SOI substrate (a substrate in which the BOX layer 2B is provided across the movable part 24, the diaphragm part 25, and the base part 26) as the first substrate 2 in the wavelength-variable interference filter 1 of this embodiment. In FIG. 5, the broken line is the spectral length spectrum of the wavelength-variable interference filter 1 of this embodiment, and the solid line is the spectral spectrum of the wavelength-variable interference filter of the comparative example. The example of FIG. 5 is the spectral spectrum when the interval of the gap G is controlled so that the primary peak transmission wavelength becomes 1700 nm in this embodiment and the comparative example. As shown in FIG. 5, in the comparative example, even in the filter region, since there are boundaries between the BOX layer 2B and the support layer 2A and between the BOX layer 2B and the active layer 2C of the SOI substrate, light reflection occurs at these boundaries. In this case, multiple reflections of light occur between the BOX layer 2B and the first reflection film 41. Due to such multiple reflections, in the wavelength-variable interference filter of the comparative example, in addition to the primary peak transmission wavelength (1700 nm in the example of FIG. 5) that is originally desired to be transmitted, a plurality of peak wavelengths appear in the vicinity of the primary peak transmission wavelength. On the other hand, as in the present embodiment, by using a special SOI substrate in which the BOX layer 2B is not provided in the filter region, unnecessary multiple reflections as described above are suppressed. Thereby, a spectral spectrum of one peak waveform centered on the primary peak transmission wavelength can be obtained.

[0022] In the present embodiment, as described above, the active layer 2C of the first substrate 2 is doped with impurities to have conductivity and functions as an electrode. On the other hand, on the second substrate 3, a drive electrode 5 is provided via an insulating layer 35 with respect to the bottom 331 of the first recess 33 so as to face the diaphragm portion 25. That is, the drive electrode 5 is formed in an annular or substantially annular shape so as to surround the second reflection film 42. Further, as shown in FIG. 3, the drive electrode 5 may have a multi-electrode structure in which a plurality of drive electrodes 5 having different diameter dimensions are arranged with respect to the second reflection film 42. In this case, by controlling the drive voltages applied to the plurality of drive electrodes 5 having different diameter dimensions respectively, the displacement of the movable portion 24 in the Z direction can be controlled more precisely. Note that in FIG. 4, for simplicity of the figure, a configuration in which a single drive electrode 5 is provided is illustrated.

[0023] Also, as shown in FIG. 3, the drive electrode 5 is electrically connected to a drive electrode terminal 52 disposed outside the cavity C via a lead wiring 51 formed on the second substrate 3. Also, as shown in FIG. 2, by cutting out a part of the first substrate 2 with respect to the second substrate 3, a part (terminal portion 36) of the second substrate 3 can be exposed to the outside as shown in FIG. 1. By providing the drive electrode terminal 52 on the terminal portion 36, it becomes possible to easily perform wiring for the drive electrode 5.

[0024] Further, when using a conductive metal bonding material as the bonding layer 6 that bonds the first substrate 2 and the second substrate 3, it is preferable to expose a part of the bonding layer 6 to the terminal portion 36. In this case, the bonding layer 6 exposed from the terminal portion 36 functions as the common electrode terminal 53, and wiring for the active layer 2C can be easily performed via the common electrode terminal 53. As wiring for the drive electrode 5 and the active layer 2C, for example, as shown in FIG. 4, a lead wire 54 may be connected to the drive electrode terminal 52 and the common electrode terminal 53, or connection by FPC (Flexible printed circuits) may be used.

[0025] In the wavelength-variable interference filter 1 having the above configuration, the common electrode terminal 53 is grounded to the ground, and when a drive voltage is input to the drive electrode terminal 52, an electrostatic attraction force acts between the active layer 2C and the drive electrode 5. As a result, the movable part 24 is displaced in the Z direction toward the second substrate 3, and the gap G is changed. That is, in the present embodiment, the active layer 2C and the drive electrode 5 of the first substrate 2 function as an actuator for changing the gap G.

[0026] [Manufacturing method of wavelength-variable interference filter 1] Next, an example of the manufacturing method of the wavelength-variable interference filter 1 of the present embodiment will be briefly described with reference to FIG. 6. First, the manufacturing of the base material of the first substrate 2 of the present embodiment will be described. FIG. 6 is a diagram showing the manufacturing process of the special SOI substrate that becomes the base material of the first substrate of the present embodiment. First, prepare a Si substrate 71 having a uniform thickness as shown in the first of FIG. 6. Then, form a resist 72 on one surface (the second surface 22 side) of the Si substrate 71, and pattern the resist 72 to form a resist opening 721 so that the portion other than the formation position of the BOX layer 2B is masked as shown in the second of FIG. 6. The position of the resist opening 721 is at least a position corresponding to the diaphragm portion 25.

[0027] Then, as shown in the third of FIG. 6, etch the portion of the Si substrate 71 exposed from the resist opening 721 to form a recess pattern 73. The etching of the Si substrate 71 may be either dry etching or wet etching. Here, when dry etching is performed, the resist opening 721 is formed larger than the diaphragm portion 25. That is, a resist pattern is formed so that a range up to a predetermined margin range centered on the diaphragm portion 25 is opened. When wet etching is performed, if a resist opening 721 corresponding to the diaphragm portion 25 is formed, a predetermined margin range centered on the diaphragm portion 25 is etched by side etching.

[0028] After that, as shown in the fourth of FIG. 6, after removing the resist 72, as shown in the fifth of FIG. 4, the surface of the Si substrate 71 is thermally oxidized. Thereby, a SiO2 layer 74 is formed on the surface of the Si substrate 71.

[0029] Then, as shown in the sixth of FIG. 6, grind the SiO2 layer 74 side of the Si substrate 71. At this time, when forming the recess pattern 73, grind the SiO2 layer so that the unetched Si surface 71A exposed by the resist 72 is exposed to a depth above the depth at which only the desired BOX layer 2B is exposed and less than the depth of the recess pattern 73. Thereby, in the Si substrate 71, the unthermally oxidized Si layer is exposed by grinding to form the support layer 2A, and the BOX layer 2B is formed by the SiO2 layer remaining in the recess pattern 73. Note that a hard mask layer 75 is formed on the surface of the Si substrate 71 opposite to the surface on which the recess pattern 73 is formed by the above thermal oxidation treatment.

[0030] Thereafter, as shown in the seventh of FIG. 6, an Si layer is formed on the surface of the Si substrate 71 where the concave pattern 73 is formed so as to cover the Si surface 71A (the surface of the support layer 2A) and the SiO2 layer 74 (BOX layer 2B). That is, the active layer 2C of Si is formed so as to cover the support layer 2A and the BOX layer 2B. The formation of the active layer 2C is performed, for example, by sputtering on the surface of the Si substrate 71 where the concave pattern 73 is formed, using a target doped with impurities such as boron (B) or phosphorus (P).

[0031] After the above, by grinding the hard mask layer 75, an SOI substrate in which the support layer 2A, the BOX layer 2B, and the active layer 2C are laminated is formed. FIG. 7 is a schematic plan view of a part of the SOI substrate that is the base material of the first substrate 2, and shows the position of the BOX layer 2B. The portion indicated by the diagonal lines in the figure shows the position where the BOX layer 2B is provided. That is, in the figure, the diagonal portion is a laminate of the support layer 2A, the BOX layer 2B, and the active layer 2C, and the portion without diagonal lines is a laminate of the support layer 2A and the active layer 2C. In the present embodiment, a plurality of first substrates 2 are formed from one base material. Therefore, as shown in FIG. 7, a plurality of annular BOX layers 2B corresponding to the diaphragm portions 25 of each first substrate 2 are formed. The first substrate 2 is formed by cutting the base material, for example, by laser cutting or the like in accordance with the shape of the first substrate 2 (see FIGS. 1 and 2). Here, an example is shown in which the first substrate 2 is cut out from the base material before bonding the second substrate 3 to the first substrate 2, but a cutting process may be performed in the shape of the wavelength variable interference filter 1 after bonding the second substrate 3 to the first substrate 2.

[0032] Next, the manufacturing of the wavelength variable interference filter 1 will be described. FIG. 8 is a diagram showing a manufacturing method of the wavelength variable interference filter 1. Note that the second substrate 3 is pre-formed, and a detailed description using FIG. 8 is omitted. The second substrate 3 is formed by grinding the base material of the second substrate 3 to a desired thickness dimension, and forming a first recess 33, a reflective film installation portion 34, and a terminal portion 36 on the third surface 31 by etching. Next, an electrode film is formed on the third surface 31, and the electrode film is patterned by etching or the like to form the drive electrode 5. Further, a second reflective film 42 is formed on the reflective film installation portion 34. The second reflective film 42 is formed, for example, by forming a lift-off pattern except for the installation locations of the second reflective film 42, then forming a dielectric multilayer film, and removing unnecessary portions by a lift-off process.

[0033] In the manufacture of the wavelength-variable interference filter, first, as shown in the first of FIG. 8, a first reflective film 41 is formed on the first surface 21 of the portion corresponding to the movable portion 24 of the first substrate 2 (the diaphragm portion 25 is not formed) of the special SOI substrate as shown in the second of FIG. 8. Further, on the second surface 22 of the first substrate 2, an antireflection film 43 may be further formed at a position overlapping the first reflective film 41 in the Z direction. The formation of the first reflective film 41 and the antireflection film 43 is the same as that of the second reflective film 42 described above, and for example, lift-off can be used.

[0034] Further, as shown in the third of FIG. 8, a bonding layer 6 is formed on the first surface 21 of the portion corresponding to the base portion 26 of the first substrate 2. The bonding layer 6 is not particularly limited, but as described above, it is preferable that a conductive bonding material (for example, a paste-like metal such as silver paste) is used as the bonding layer 6, and a part of the conductive bonding material is exposed to the terminal portion 36. Thereby, wiring such as a lead wire can be easily connected to the conductive bonding material exposed from the terminal portion 36. Further, when an electrode in contact with the active layer 2C is provided separately, a non-conductive material may be used as the bonding layer 6, and examples thereof include a plasma polymerization film mainly composed of siloxane, a low melting point glass, and an epoxy resin.

[0035] Next, as shown in the fourth of FIG. 8, the first substrate 2 and the second substrate 3 are bonded by the bonding layer 6. Thereafter, as shown in the fifth of FIG. 8, the support layer 2A of the diaphragm portion 25 of the first substrate 2 is dry-etched using the BOX layer 2B as an etching stopper to form a groove 23. Here, the BOX layer 2B is formed in a range including a predetermined margin range centering on the diaphragm portion 25. Therefore, it is possible to suppress the disadvantage that the active layer 2C in the portion where the BOX layer 2B is not provided is etched by dry etching, and a diaphragm portion 25 having a uniform thickness dimension can be formed. Also, in the present embodiment, since the diaphragm portion 25 is created by dry etching using the BOX layer 2B of the SOI substrate as an etching stopper, the side wall 23A and the bottom surface 25B of the diaphragm portion 25 are perpendicular or substantially perpendicular. Thereby, compared with the case where the diaphragm portion 25 is formed by wet etching, the occurrence of side etching can be suppressed, so that the wavelength-variable interference filter 1 can be miniaturized and the filter region can be enlarged in diameter.

[0036] [Operational Effects of the Present Embodiment] The wavelength-variable interference filter 1 of the present embodiment includes a first substrate 2 provided with a first reflective film 41 and a second substrate 3 provided with a second reflective film 42 facing the first reflective film 41 with a gap G therebetween. The first substrate 2 is an SOI substrate having layers in the order of a support layer 2A which is an Si layer, a BOX layer 2B which is an SiO2 layer, and an active layer 2C composed of Si along the Z direction. The first substrate 2 includes a movable portion 24 provided with the first reflective film 41, a diaphragm portion 25 surrounding the movable portion 24 when viewed from the Z direction, and a base portion 26 surrounding the diaphragm portion 25 when viewed from the Z direction and supporting the movable portion 24 so as to be able to advance and retreat in the Z direction via the diaphragm portion 25. And the diaphragm portion 25 is a portion having a thickness thinner in the Z direction than the base portion 26 by a groove 23 opening to the second surface 22 on the side opposite to the second substrate 3 of the first substrate 2, and is composed of the BOX layer 2B and the active layer 2C, and at least the first surface of the base portion 26 and the diaphragm portion 25 of the first substrate 2 is configured to be flat in a state where the movable portion 24 is not displaced.

[0037] The first substrate 2 is a substrate with an SOI substrate as the base material, and by providing a BOX layer 2B which is an SiO2 layer, dry etching can be performed using the BOX layer 2B as an etching stopper. By forming a groove 23 through dry etching, residual Si of the support layer 2A does not occur on the BOX layer 2B, and a diaphragm portion 25 with a uniform thickness composed of the BOX layer 2B and the active layer 2C can be realized. In addition, since side etching such as when wet etching a single material substrate does not occur, the wavelength-variable interference filter 1 can be downsized accordingly, and a large-diameter filter region can be secured within the limited overall size.

[0038] In the wavelength-variable interference filter 1 of the present embodiment, the active layer is composed of Si doped with impurities. Thereby, conductivity can be imparted to the active layer 2C, the active layer 2C can be used as an electrode, and the steps of separately forming a metal film and patterning the metal film can be made unnecessary.

[0039] In the wavelength-variable interference filter 1 of the present embodiment, the impurities are B (boron) or P (phosphorus). By doping B or P into the Si layer, improvement in conductivity, that is, reduction in resistance when used as an electrode can be achieved.

[0040] In the wavelength-variable interference filter 1 of the present embodiment, when the first substrate 2 is viewed from the Z direction, the BOX layer 2B is provided in a closed annular shape surrounding the movable portion 24, and the first surface 21 on the side facing the second substrate 3 of the movable portion 24, the diaphragm portion 25, and the base portion 26 is flat when the movable portion 24 is not displaced. That is, in the present embodiment, the first surface 21 of the first substrate 2 has a shape covered by the active layer 2C. When the active layer 2C is used as an electrode facing the drive electrode 5, if there is variation in the initial value of the distance between the drive electrode 5 and the active layer 2C, in-plane variation occurs in the electrostatic attraction due to voltage application, and the movable portion 24 tilts. In contrast, in the present embodiment, since the distance between the drive electrode 5 and the active layer 2C is uniform, tilting of the movable portion 24 can be suppressed when the movable portion 24 is displaced.

[0041] [Second Embodiment] The wavelength-variable interference filter 1 of the first embodiment is an example in which the first substrate 2 is constituted by a special SOI substrate provided with a BOX layer 2B up to a predetermined margin range centering on the diaphragm portion 25. In contrast, the second embodiment is different from the first embodiment in that a normal SOI substrate in which the BOX layer 2B is formed over the entire substrate is used. In the following description, the same reference numerals are given to the matters already described, and the description thereof is omitted or simplified.

[0042] FIG. 9 is a cross-sectional view showing a schematic configuration of the wavelength-variable interference filter 1A according to the second embodiment. In the wavelength-variable interference filter 1A of the present embodiment, as shown in FIG. 9, a first substrate 20, a second substrate 3, a first reflective film 41, a second reflective film 42, and a drive electrode 5 are provided. Since the second substrate 3, the first reflective film 41, the second reflective film 42, and the drive electrode 5 are the same as those in the first embodiment, the description thereof is omitted here.

[0043] As described above, the first substrate 20 of the present embodiment is based on a normal SOI substrate, and in the base material, a support layer 2A, a BOX layer 2B, and an active layer 2C are provided over the entire substrate. In the present embodiment, by appropriately processing the base material, in the formation position of the first reflective film 41 of the movable portion 24, the BOX layer 2B and the active layer 2C are removed. Therefore, a facing recess 27 (the concave groove of the present disclosure) facing the second substrate 3 is provided on the first surface 21 of the movable portion 24. The bottom surface of the facing recess 27 facing the second substrate 3 is a portion where the support layer 2A is exposed, and the first reflective film 41 is provided on the bottom surface of the facing recess 27. That is, in the present embodiment, the base portion 26 is constituted by the support layer 2A, the BOX layer 2B, and the active layer 2C, and the diaphragm portion 25 is constituted by the BOX layer and the active layer 2C. Among the movable portion 24, the vicinity of the boundary with the diaphragm portion 25 (the portion where the first reflective film 41 is not provided) is constituted by the support layer 2A, the BOX layer 2B, and the active layer 2C, and the central portion of the movable portion 24 where the first reflective film 41 is provided is constituted by the support layer 2A. In such a configuration, the surface portion of the first surface 21 of the first substrate 20 where the opposing recess 27 is not provided is flat in a state where the movable portion 24 is not displaced in the Z direction.

[0044] [Method for manufacturing the wavelength-variable interference filter 1A] FIG. 10 is a diagram showing a method for manufacturing the wavelength-variable interference filter 1A of the present embodiment. For the wavelength-variable interference filter 1A of the present embodiment, a first substrate 20 of a normal SOI substrate (the diaphragm portion 25 is not formed) as shown in the first of FIG. 10 is prepared. Then, as shown in the second of FIG. 10, an opposing recess 27 (the groove of the present disclosure) is formed on the active layer 2C side of the first substrate 20 in accordance with the formation position of the first reflective film 41. The opposing recess 27 can be formed, for example, by a two-step etching in which the active layer 2C, which is a Si layer, is etched with HNO3 and then the BOX layer 2B, which is a SiO2 layer, is etched with HF.

[0045] The subsequent processing is the same as that from the second of FIG. 8 onwards. That is, as shown in the third of FIG. 10, the first reflective film 41 is formed in the opposing recess 27. At this time, an antireflection film 43 may be formed on the second surface 22 of the first substrate 20 on the side opposite to the first reflective film 41. Also, a bonding layer 6 is formed on the base portion 26. Then, as shown in the fifth of FIG. 10, the second substrate 3 provided with the second reflective film 42 and the drive electrode 5 and the first substrate 20 are bonded via the bonding layer 6. After this, the second surface 22 of the first substrate 20 is dry-etched using the BOX layer 2B as an etching stopper to form the groove 23, thereby shaping the shapes of the movable portion 24, the diaphragm portion 25, and the base portion 26. Thus, the wavelength-variable interference filter 1A is manufactured.

[0046] [Advantages and effects of the present embodiment] In the wavelength-variable interference filter 1A of the present embodiment, in addition to the advantages and effects of the wavelength-variable interference filter 1 of the first embodiment, the following effects can be achieved. In this embodiment, the movable portion 24 of the first substrate 20 is provided with a counter recess 27 penetrating the active layer 2C and the BOX layer 2B on the first surface 21 facing the second substrate 3. The support layer 2A is exposed on the groove bottom surface of the counter recess 27, and a first reflective film 41 is provided on the groove bottom surface. In this case, as the first substrate 20, a normal SOI substrate can be formed using a mother material, and the manufacturing process can be reduced as compared with the case of using a special SOI substrate.

[0047] [Modification Example] Note that the present invention is not limited to the above-described embodiment, and modifications, improvements, etc. within the scope that can achieve the object of the present invention are included in the present invention.

[0048] [Modification Example 1] In the above first embodiment, an example is shown in which a part of the bonding layer 6 of the conductive bonding material is exposed on the terminal portion 36 provided on the second substrate 3 to function as the common electrode terminal 53. However, the present invention is not limited to this. For example, the support layer 2A may be formed of a Si layer doped with impurities such as B or P, similar to the active layer 2C. In this case, for example, wiring such as a lead wire can be directly connected to a part of the first substrate 2 such as the second surface 22 of the base portion 26. Further, in this case, the bonding layer 6 is not limited to a conductive bonding material, and various bonding materials such as a plasma polymerization film, a low melting point glass, and an epoxy resin can be used.

[0049] [Modification Example 2] In the second embodiment, with respect to a normal SOI substrate in which the active layer 2C is formed over the entire substrate, by providing the counter recess 27, the BOX layer 2B in the filter region is removed, and a configuration is adopted to suppress multiple reflections between the BOX layer 2B and the first reflective film 41. On the other hand, a special SOI substrate as in the first embodiment, that is, an SOI substrate in which the BOX layer 2B is embedded at a predetermined position may be used. FIG. 11 is a schematic plan view of a first substrate (SOI substrate 70A which is a base material) before the formation of the diaphragm portion 25 according to Modification 2. The portion indicated by hatching in the figure shows the position where the BOX layer 2B is provided. That is, in the figure, the hatched portion is a laminate of the support layer 2A, the BOX layer 2B, and the active layer 2C, and the portion without hatching is a laminate of the support layer 2A and the active layer 2C. In this case, it is not necessary to form the opposing recess 27 by etching, and a wavelength-variable interference filter can be manufactured by the same manufacturing method as in the first embodiment. In this configuration, as in the first embodiment, the surface of the first substrate facing the second substrate 3 is composed of the active layer 2C of the SOI substrate, and becomes flat in a state where the movable portion 24 is not displaced in the Z direction.

[0050] [Modification 3] In the above first embodiment, when viewed from the Z direction, the shape of the BOX layer 2B is an annular shape corresponding to the shape of the diaphragm portion 25, and in the second embodiment, an example in which the opposing recess 27 is an annular shape is shown, but the present invention is not limited thereto. The shape of the BOX layer 2B and the shape of the opposing recess 27 are not particularly limited as long as they are closed annular shapes, and may be formed in an ellipse or a polygon. For example, it may be formed in a hexagonal shape along the Si plane orientation.

[0051] [Summary of the Present Disclosure] The wavelength-variable interference filter according to the first aspect of the present disclosure includes a first substrate provided with a first reflective film, and a second substrate provided with a second reflective film facing the first reflective film through a gap. The first substrate is an SOI substrate having layers in the order of a first layer made of Si, a second layer made of SiO2, and a third layer made of Si along the thickness direction from the first substrate toward the second substrate. The first substrate includes a movable portion where the first reflective film is provided, a diaphragm portion surrounding the movable portion when viewed from the thickness direction from the first substrate toward the second substrate, and a base portion surrounding the diaphragm portion when viewed from the thickness direction and supporting the movable portion so as to be movable along the thickness direction through the diaphragm portion. The diaphragm portion is a portion having a thickness thinner than that of the base portion in the thickness direction by a groove opening on the surface of the first substrate opposite to the second substrate, and is composed of the second layer and the third layer. At least the surfaces of the base portion and the diaphragm portion of the first substrate on the second substrate side are flat when the movable portion is not displaced.

[0052] In such an aspect, since the first substrate is a substrate having an SOI substrate as a base material, dry etching capable of forming a groove in the first layer using the second layer as an etching stopper becomes possible. For this reason, the diaphragm portion can be composed of the second layer and the third layer, and a diaphragm portion having a uniform thickness can be realized. In addition, since side etching does not occur as in the case of wet etching a single material substrate, miniaturization of the wavelength-variable interference filter becomes possible, and it is possible to increase the diameter of the area (filter region) where the first reflective film and the second reflective film face each other within a limited overall size.

[0053] In the wavelength-variable interference filter of this aspect, it is preferable that the third layer is composed of Si doped with impurities. Thereby, conductivity can be imparted to the Si layer of the third layer, there is no need to separately form an electrode on the substrate, the configuration can be simplified, and the manufacturing process can be simplified when manufacturing the wavelength-variable interference filter.

[0054] In the wavelength-variable interference filter of this aspect, it is preferable that the impurity is boron or phosphorus. Thereby, the Si layer of the third layer can be made highly conductive and can function more preferably as an electrode.

[0055] In the wavelength-variable interference filter of this aspect, in the surface of the movable part facing the second substrate, concave grooves penetrating the second layer and the third layer in the thickness direction are provided, the groove bottom surface of the concave grooves is the surface of the first layer, and it is preferable that the first reflection film is provided on the groove bottom surface. Thereby, at the position where the first reflection film is provided, since the second layer which is an SiO2 layer is not provided, there is no multiple reflection between the first reflection film and the second layer, and light of a desired wavelength can be preferably output from the wavelength-variable interference filter.

[0056] In the wavelength-variable interference filter of this aspect, when the first substrate is viewed from the thickness direction, the second layer is provided in a closed annular shape surrounding the movable part, and the surfaces of the movable part, the diaphragm part, and the base part facing the second substrate are preferably flat when the movable part is not displaced. In this aspect, since the second layer is not provided in the portion where the first reflection film is provided, similar to the above aspect, there is no multiple reflection between the first reflection film and the second layer, and light of a desired wavelength can be preferably output from the wavelength-variable interference filter. Further, since the surfaces of the diaphragm part and the base part facing the second substrate are flat, when the third layer of the diaphragm part functions as an electrode, the distance between the third layer and the drive electrode provided on the second substrate can be made uniform, and the inclination of the movable part can be suppressed when the movable part is displaced.

[0057] In the wavelength-variable interference filter of this aspect, when the first substrate is viewed from the thickness direction, the second layer is not provided on the movable part, is provided on the diaphragm part and the base part, and the surfaces of the movable part, the diaphragm part, and the base part facing the second substrate may be configured to be flat when the movable part is not displaced. Also in this aspect, since the second layer is not provided in the portion where the first reflective film is provided, similar to the above aspect, there is no multiple reflection between the first reflective film and the second layer, and light of a desired wavelength can be preferably output from the wavelength-variable interference filter. Further, since the surfaces of the diaphragm portion and the base portion facing the second substrate are flat, when the third layer of the diaphragm portion functions as an electrode, the distance between the third layer and the drive electrode provided on the second substrate can be made uniform, and when the movable portion is displaced, the inclination of the movable portion can be suppressed.

Explanation of Signs

[0058] 1, 1A... Wavelength-variable interference filter, 2... First substrate, 2A... Support layer (first layer), 2B... BOX layer (second layer), 2C... Active layer (third layer), 3... Second substrate, 5... Drive electrode, 6... Bonding layer, 20... First substrate, 21... First surface, 22... Second surface, 23... Groove, 23A... Side wall, 23B... Bottom surface, 24... Movable portion, 25... Diaphragm portion, 25B... Bottom surface, 26... Base portion, 27... Opposing concave portion, 31... Third surface, 32... Fourth surface, 33... First concave portion, 34... Reflective film installation portion, 35... Insulating layer, 36... Terminal portion, 41... First reflective film, 42... Second reflective film, 43... Antireflection film.

Claims

1. a first substrate provided with a first reflective film; a second substrate provided with a second reflective film facing the first reflective film with a gap therebetween, and comprising: The first substrate is an SOI substrate having layers in the order of a first layer made of Si, a second layer made of SiO ２ , and a third layer made of Si, along the thickness direction from the first substrate toward the second substrate. the first substrate includes: a movable portion provided with the first reflective film; a diaphragm portion surrounding the movable portion when viewed from the thickness direction from the first substrate toward the second substrate; a base portion surrounding the diaphragm portion when viewed from the thickness direction and supporting the movable portion so as to be movable along the thickness direction via the diaphragm portion; the diaphragm portion is a portion having a thickness thinner than that of the base portion in the thickness direction by a groove opening on a surface of the first substrate opposite to the second substrate, and is composed of the second layer and the third layer; at least the surface of the base portion and the diaphragm portion of the first substrate on the second substrate side is flat when the movable portion is not displaced; a wavelength tunable interference filter.

2. the third layer is composed of Si doped with impurities; the wavelength tunable interference filter according to claim 1.

3. the impurities are boron or phosphorus; the wavelength tunable interference filter according to claim 2.

4. the movable portion is provided with concave grooves penetrating the second layer and the third layer in the thickness direction on a surface facing the second substrate, a bottom surface of the concave groove is a surface of the first layer, and the first reflective film is provided on the bottom surface of the groove; the wavelength tunable interference filter according to claim 1.

5. when the first substrate is viewed from the thickness direction, the second layer is provided in a closed annular shape surrounding the movable portion; the surfaces of the movable portion, the diaphragm portion, and the base portion on the side facing the second substrate are flat when the movable portion is not displaced; the wavelength tunable interference filter according to claim 1.

6. when the first substrate is viewed from the thickness direction, the second layer is not provided on the movable portion, but is provided on the diaphragm portion and the base portion; the surfaces of the movable portion, the diaphragm portion, and the base portion on the side facing the second substrate are flat when the movable portion is not displaced; the wavelength tunable interference filter according to claim 1.

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