Optical filter and method for manufacturing optical filter

Abstract

The invention provides an optical filter and a method for manufacturing the optical filter, which can suppress aggregation of silver or silver alloy constituting a reflective film and thereby suppress reduction of optical characteristics. This optical filter is provided with: a first substrate; a second substrate facing the first substrate with a gap therebetween; a first underlayer provided on a surface of the first substrate facing the second substrate; a second underlayer provided on a surface of the second substrate facing the first substrate; a first reflective film which is provided on the first substrate with the first underlayer interposed therebetween and which is composed of silver or a silver alloy; and a second reflective film that is provided on the second substrate with the second underlayer interposed therebetween and is composed of silver or a silver alloy, the maximum height roughness of the first underlayer and the second underlayer being 7.3 nm or more.

Description

Technical Field

[0001] The present invention relates to an optical filter and a method for manufacturing the optical filter. Background Art

[0002] Conventionally, there is known a technique for using a metal film such as silver or a silver alloy as a reflective film in an optical filter having a substrate on which a reflective film is formed (for example, see Patent Document 1).

[0003] Patent Document 1 discloses a structure in which a metal film is formed on a glass substrate and covered with a barrier layer to suppress degradation of the metal film. Patent Document 1 also discloses a structure in which a dielectric film is formed on a glass substrate and a metal film is formed on the dielectric film and covered with a protective layer.

[0004] However, when silver or a silver alloy is formed on a glass substrate, there is a problem in that the silver or the silver alloy aggregates due to high temperatures in the manufacturing process or the use environment, thereby reducing optical properties such as transmittance and reflectivity.

[0005] Patent Document 1: Japanese Patent Application Laid-Open No. 2012-42584 Summary of the Invention

[0006] The optical filter of the first embodiment of the present invention comprises: a first substrate; a second substrate, which is opposite to the first substrate with a gap therebetween; a first base layer, which is arranged on the surface of the first substrate opposite to the second substrate; a second base layer, which is arranged on the surface of the second substrate opposite to the first substrate; a first reflective film, which is arranged on the first substrate with the first base layer therebetween and is composed of silver or a silver alloy; a second reflective film, which is arranged on the second substrate with the second base layer therebetween and is composed of silver or a silver alloy, and the maximum height roughness of the first base layer and the second base layer is not less than 7.3 nm.

[0007] The second embodiment of the present invention provides a method for manufacturing an optical filter, wherein the optical filter comprises a substrate, a base layer provided on the substrate, and a reflective film composed of silver or a silver alloy provided on the substrate via the base layer. The method for manufacturing the optical filter comprises: a base process for forming the base layer on the substrate by sputtering; and a reflective film process for forming the reflective film on the base layer. In the base process, the base layer is formed in such a manner that the maximum height roughness of the base layer becomes greater than 7.3 nm. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1It is a cross-sectional view showing a schematic structure of an interference filter according to one embodiment of the present disclosure.

[0009] Figure 2 This is a flowchart showing a method for manufacturing the interference filter according to this embodiment.

[0010] Figure 3 A diagram showing each step of the first substrate forming process.

[0011] Figure 4 A diagram showing each step of the second substrate forming process.

[0012] Figure 5 This diagram shows the presence or absence of silver alloy coagulation when a TiO2 base layer is formed on a chip substrate by changing the flow rate of inert gas (Ar) and O2, and a silver alloy (Ag-Bi-Nd) film is formed on the base layer and then heated to 400°C.

[0013] Figure 6 This is a graph showing the maximum surface height Rz in a 2 μm square relative to the film thickness of the base layer.

[0014] Figure 7 This is a graph showing the maximum surface height Rz in a 5 μm square relative to the film thickness of the base layer.

[0015] Figure 8 Graphs showing the transmittance of the interference filter of this embodiment before heating and after heating to 400°C.

[0016] Figure 9 It is a graph showing the transmittance of the interference filter of the comparative example before heating and the transmittance after heating to 400°C.

[0017] Figure 10 This figure shows an example of a binarized image obtained by heating the interference filter of the present embodiment to 400° C., capturing an image of the reflective film, and binarizing the captured image using a predetermined threshold value.

[0018] Figure 11 It is a schematic cross-sectional view of an interference filter according to a modification. DETAILED DESCRIPTION

[0019] Hereinafter, an interference filter will be described as an optical filter according to one embodiment of the present disclosure. Figure 1 3 is a cross-sectional view showing a schematic structure of the interference filter according to the present embodiment.

[0020] The interference filter 1 of this embodiment is an optical filter disclosed herein and includes a first substrate 11 and a second substrate 12 that face each other. A first base layer 21 and a first reflective film 31 are provided on the surface of the first substrate 11 that faces the second substrate 12, and are provided on the first substrate 11 via the first base layer 21.

[0021] Similarly, a second base layer 22 and a second reflective film 32 provided on the second substrate 12 via the second base layer 22 are provided on the surface of the second substrate 12 facing the first substrate 11 .

[0022] Furthermore, first drive electrodes 41 and first detection electrodes 51 are provided on the surface of the first substrate 11 that faces the second substrate 12. Second drive electrodes 42 facing the first drive electrodes 41 and second detection electrodes 52 facing the first detection electrodes 51 are provided on the surface of the second substrate 12 that faces the first substrate 11.

[0023] In the following description, the direction from the first substrate 11 toward the second substrate 12 is referred to as the Z direction, the direction perpendicular to the Z direction is referred to as the X direction, and the direction perpendicular to the Z and X directions is referred to as the Y direction. The Z direction corresponds to the thickness direction of the interference filter 1 .

[0024] Structure of the first substrate 11

[0025] The first substrate 11 is formed by appropriately processing any one of quartz, alkali-free glass, and borosilicate glass into a certain shape.

[0026] Specifically, the first substrate 11 has a first surface 11A that faces the second substrate 12, and a second surface 11B on the opposite side of the first surface 11A. A groove 111, for example, in the shape of an annulus, is formed on the second surface 11B of the first substrate 11. The portion of the first substrate 11 surrounded by the groove 111 is referred to as the movable portion 112, the portion of the first substrate 11 where the groove 111 surrounds the movable portion 112 is referred to as the diaphragm portion 113, and the portion outside the diaphragm portion 113 is referred to as the outer peripheral base portion 114. The diaphragm portion 113 connects the movable portion 112 and the outer peripheral base portion 114 and supports the movable portion 112 so that it can be displaced in the Z direction.

[0027] The outer peripheral base portion 114 of the first substrate 11 is bonded to the second substrate 12 via the bonding film 13 .

[0028] Structure of the first base layer 21

[0029] The first base layer 21 is provided on the first surface 11A side of the movable portion 112 .

[0030] In this embodiment, the first detection electrode 51 is formed in a ring shape surrounding the first reflection film 31, and the first base layer 21 overlaps the inner circumference of the first detection electrode 51 and is formed on the first detection electrode 51. Figure 1 In the example, an example is shown in which the first detection electrode 51 is formed on the first substrate 11 and the first base layer 21 is formed therefrom, but a structure in which the first base layer 21 is formed on the first substrate 11 and the first detection electrode 51 is formed therefrom can also be used.

[0031] The first base layer 21 is a layer formed of any one of TiO 2 , Nb 2 O 5 , Ta 2 O 5 , HfO 2 , ZrO 2 , ITO, and IGO.

[0032] Although the details will be described later, the first base layer 21 is formed to have a surface roughness (maximum height roughness Rz) of 7.3 nm or more. More specifically, the maximum height roughness Rz in a 2 μm square is 7.3 nm or more, and the maximum height roughness Rz in a 5 μm square is 9.9 nm or more.

[0033] Structure of the first reflective film 31

[0034] The first reflective film 31 is provided on the first base layer 21 on the first surface 11A side of the movable portion 112. That is, the first reflective film 31 is provided on the first substrate 11 via the first base layer 21.

[0035] The first reflective film 31 is, for example, a film made of silver or a silver alloy, and more preferably, made of either Ag—Bi—Nd or Ag—Sm—Cu.

[0036] Although the details will be described later, since the first reflective film 31 is formed on the first base layer 21 having a maximum height roughness Rz of 7.3 nm or more, even when the interference filter 1 is exposed to high temperatures, the aggregation of the first reflective film 31 is suppressed, thereby suppressing the degradation of the optical properties (reflectivity or transmittance) caused by the aggregation.

[0037] Structure of the first driving electrode 41

[0038] The first drive electrode 41 is provided in a generally annular shape at the location of the diaphragm portion 113 on the first surface 11A of the first substrate 11. The first drive electrode 41 is opposed to the second drive electrode 42 provided on the second substrate 12, and together with the second drive electrode 42, constitutes an electrostatic actuator. Specifically, by applying a predetermined drive voltage between the first drive electrode 41 and the second drive electrode 42, an electrostatic attractive force corresponding to the drive voltage acts between the first drive electrode 41 and the second drive electrode 42, thereby causing the diaphragm portion 113 to flex, thereby displacing the movable portion 112 in the Z direction.

[0039] Structure of the first detection electrode 51

[0040] As described above, the first detection electrode 51 is formed in a ring shape along the periphery of the first reflective film 31 in the movable portion 112 , and the first base layer 21 is stacked on the inner peripheral side (the center side of the movable portion 112 ) facing the second substrate 12 .

[0041] Furthermore, by forming the first reflection film 31 to cover the first base layer 21 , the outer periphery of the first reflection film 31 contacts the first detection electrode 51 from the side surface of the first base layer 21 , thereby achieving electrical conduction between the first reflection film 31 and the first detection electrode 51 .

[0042] The first detection electrode 51 functions as a capacitance detection electrode together with the second detection electrode 52 provided on the second substrate 12. For example, by using the first detection electrode 51, which is electrically connected to the first reflective film 31, and the second detection electrode 52, which is electrically connected to the second reflective film 32, the capacitance between the first reflective film 31 and the second reflective film 32 is detected, thereby enabling calculation of the distance between the first reflective film 31 and the second reflective film 32.

[0043] In addition, the first detection electrode 51 may be connected to the ground to discharge the electric charge of the first reflection film 31 .

[0044] Structure of the second substrate 12

[0045] Similar to the first substrate 11 , the second substrate 12 is formed by appropriately processing any one of quartz, alkali-free glass, and borosilicate glass into a certain shape.

[0046] Specifically, the second substrate 12 has a third surface 12A facing the first substrate 11. On this third surface 12A, a recessed portion 121 is provided at a position facing the movable portion 112 and the diaphragm portion 113. Furthermore, in this embodiment, a protrusion 122 is provided at the center of the recessed portion 121, protruding toward the first substrate 11. The surface of the protrusion 122 facing the first substrate 11 is a flat surface parallel to the XY plane. While this embodiment shows an example in which the protrusion 122 is provided, in order to increase the distance between the first and second reflective films 31 and 32, a recessed portion, concave away from the first substrate 11, may be provided at the center of the recessed portion 121 in place of the protrusion 122.

[0047] A substrate-joining portion 123 is provided on the outer periphery of the second substrate 12, which is joined to the outer peripheral base portion 114 of the first substrate 11. A groove (not shown) communicating with the recess 121 is provided in a portion of the substrate-joining portion 123. Lead electrodes (not shown) for the first and second drive electrodes 41 and 42, and the first and second detection electrodes 51 and 52, are led out through this groove to the outer periphery of the second substrate 12.

[0048] Structure of the second base layer 22

[0049] The second base layer 22 is provided on the third surface 12A side of the second substrate 12 .

[0050] In this embodiment, the second detection electrode 52 facing the first detection electrode 51 is formed in a ring shape surrounding the second reflective film 32, and the second base layer 22 is formed on the second detection electrode 52 so as to overlap the inner circumference of the second detection electrode 52. Figure 1 In the example, an example is shown in which the second detection electrode 52 is formed on the second substrate 12 and the second base layer 22 is formed therefrom, but it can also be set to the following structure, that is, the second base layer 22 is formed on the second substrate 12 and the second detection electrode 52 is formed therefrom.

[0051] Similar to the first base layer 21 , the second base layer 22 is a layer formed of any one of TiO 2 , Nb 2 O 5 , Ta 2 O 5 , HfO 2 , ZrO 2 , ITO, and IGO.

[0052] Similar to the first base layer 21 , the second base layer 22 is formed to have a surface roughness (maximum height roughness Rz) of 7.3 nm or more. More specifically, the maximum height roughness Rz in a 2 μm square is 7.3 nm or more, and the maximum height roughness Rz in a 5 μm square is 9.9 nm or more.

[0053] Structure of the second reflective film 32

[0054] The second reflective film 32 faces the first reflective film 31 and is provided on the second base layer 22, extending from the top surface of the protrusion 122 of the second substrate 12 to the bottom surface of the recess 121. In other words, the second reflective film 32 is provided on the second substrate 12 via the second base layer 22.

[0055] The second reflective film 32 is, for example, a film made of silver or a silver alloy, and more preferably, made of either Ag—Bi—Nd or Ag—Sm—Cu.

[0056] In this embodiment, the second reflective film 32 is formed on the second base layer 22 having a maximum height roughness Rz of 7.3 nm or more. Therefore, even when the interference filter 1 is exposed to high temperature, the aggregation of the second reflective film 32 is suppressed, thereby suppressing the degradation of the optical properties (reflectivity or transmittance) caused by the aggregation.

[0057] Structure of the second driving electrode 42

[0058] The second drive electrode 42 is provided in a substantially annular shape at a position facing the first drive electrode 41 on the third surface 12A of the second substrate 12. The second drive electrode 42 and the first drive electrode 41 together constitute an electrostatic actuator.

[0059] Structure of the second detection electrode 52

[0060] As described above, the second detection electrode 52 is formed in a ring shape along the circumference of the second reflection film 32 in the recessed portion 121 , and the second base layer 22 is stacked on the inner peripheral side.

[0061] Furthermore, by forming the second reflection film 32 to cover the second base layer 22 , the outer periphery of the second reflection film 32 contacts the second detection electrode 52 from the side surface of the second base layer 22 , thereby achieving electrical conduction between the second reflection film 32 and the second detection electrode 52 .

[0062] As described above, the second detection electrode 52 functions as an electrode for capacitance detection together with the first detection electrode 51. Alternatively, the second detection electrode 52 may be connected to the ground to discharge the charge of the second reflective film 32.

[0063] Method for manufacturing interference filter 1

[0064] Next, a method for manufacturing the above-described interference filter 1 will be described.

[0065] Figure 2 2 is a flowchart showing a method for manufacturing the interference filter 1 .

[0066] like Figure 2 As shown, the interference filter 1 of this embodiment is manufactured by performing the first substrate forming step S1, the second substrate forming step S2, and the bonding step S3. The first substrate forming step S1 and the second substrate forming step S2 may be performed in reverse order.

[0067] Figure 3 2 is a diagram showing each step of the first substrate forming step S1.

[0068] In the first substrate forming step S1, first, the glass substrate that will become the base material of the first substrate 11 is ground to a desired thickness, and then the grooves 111 are formed on the second surface 11B by etching. Figure 3 As shown in the first figure, the first substrate 11 including the movable portion 112, the diaphragm portion 113, and the outer peripheral base portion 114 is formed (step S11).

[0069] Next, an electrode film is formed on the first surface 11A of the first substrate 11, and patterning is performed using etching or the like (step S12). Figure 3 As shown in the second figure, the first driving electrodes 41 and the first detecting electrodes 51 are formed.

[0070] Next, the first base layer 21 is formed on the first surface 11A of the first substrate 11 (base forming process: step S13 ).

[0071] In this base step, the first base layer 21 is formed on the first substrate 11 by sputtering. Specifically, the first substrate 11 and a raw material for forming the first base layer 21, which is composed of TiO2, are placed in a vacuum chamber. Then, an inert gas such as argon and O2 are introduced into the vacuum chamber so that the amount of O2 relative to the inert gas is 1 / 9 or more. A voltage is applied with the raw material (TiO2) serving as the cathode and the first substrate 11 as the anode.

[0072] Thus, the first underlayer 21 is formed on the surface of the first substrate 11 by sputtering, and the surface roughness (maximum height roughness Rz) of the first underlayer 21 becomes 7.3 nm or more.

[0073] Then, the first base layer 21 is patterned by etching. Figure 3As shown in the third figure, the first base layer 21 is formed on the first substrate 11.

[0074] Then, the first reflective film 31 is formed on the first substrate 11 by, for example, sputtering, silver or a silver alloy, which is a raw material for forming the first reflective film 31, and then patterned by etching (reflective film process: step S14). Figure 3 As shown in the fourth figure, the first reflective film 31 is formed on the first substrate 11.

[0075] Figure 4 2 is a diagram showing each step of the second substrate forming step S2.

[0076] In the second substrate forming step S2, first, the glass substrate to be the base material of the second substrate 12 is ground to a desired thickness, and the third surface 12A is etched in two stages to form the recessed portion 121 and the protruding portion 122. Figure 4 As shown in the first figure, the outer shape of the second substrate 12 is formed (step S21).

[0077] Next, an electrode film is formed on the third surface 12A of the second substrate 12, and patterning is performed using etching or the like (step S22). Figure 4 As shown in the second figure, the second driving electrodes 42 and the second detecting electrodes 52 are formed.

[0078] Next, the second base layer 22 is formed on the third surface 12A of the second substrate 12 (base forming process: step S23 ).

[0079] In step S23, the second base layer 22 is formed using the same method as step S13. Specifically, the second substrate 12 and a raw material for forming the second base layer 22, which is composed of TiO2, are placed in a vacuum chamber. An inert gas, such as argon, and O2 are then introduced into the vacuum chamber so that the amount of O2 relative to the inert gas is 1 / 9 or greater. A voltage is applied with the raw material (TiO2) serving as the cathode and the second substrate 12 serving as the anode.

[0080] Thus, the second base layer 22 is formed on the surface of the second substrate 12 by sputtering, and the surface roughness (maximum height roughness Rz) of the second base layer 22 becomes 7.3 nm or more.

[0081] Thereafter, the second base layer 22 is patterned by etching. Figure 4 As shown in the third figure, the second base layer 22 is formed on the second substrate 12.

[0082] Then, the second reflective film 32 is formed on the second substrate 12 by, for example, sputtering, silver or a silver alloy, which is a raw material for forming the second reflective film 32, and then patterned by etching (reflective film process: step S24). Figure 4 As shown in the fourth figure, the second reflective film 32 is formed on the second substrate 12.

[0083] After the above steps, the first substrate 11 formed in the first substrate forming step S1 and the second substrate 12 formed in the second substrate forming step S2 are bonded together via the bonding film 13. In this way, the interference filter 1 is manufactured.

[0084] Optical properties of the first reflective film 31 and the second reflective film 32

[0085] Next, the optical characteristics of the first reflection film 31 and the second reflection film 32 of the interference filter 1 will be described.

[0086] In the interference filter 1 described above, even when used in a high-temperature environment or when the manufacturing process includes a heating step, the optical characteristics of the first reflection film 31 and the second reflection film 32 can be maintained.

[0087] First, the difference in the surface roughness of the base layer caused by the amount of O 2 introduced in the base step (step S13 and step S23 ) will be described.

[0088] Figure 5 This figure shows the presence or absence of silver alloy coagulation when a TiO2 base layer is formed on a chip substrate by changing the flow rate of inert gas (Ar) and O2, and a silver alloy (Ag-Bi-Nd) film is formed on the base layer and then heated to 400°C.

[0089] When a silver alloy film was formed on a wafer substrate without forming a TiO2 base layer, white turbidity was observed over the entire silver alloy due to heating. This indicates that the silver alloy aggregated over the entire wafer substrate.

[0090] When the O2 flow rate was set to 4 (sccm) and the inert gas (Ar) flow rate was set to 100 (sccm) and a TiO2 base layer was formed on a wafer substrate, the white turbidity area was reduced compared to the case where O2 was not introduced, but a few stripe-shaped white turbidity areas were observed in a narrow range. In addition, "sccm" is a unit of flow rate, which represents the volume (cm2) introduced per minute under atmospheric pressure (1 atm = 1013 hPa) and 0°C. 3 / min).

[0091] In contrast, when the flow rate of O2 is set to 1 / 9 or more relative to the flow rate of the inert gas, that is, when the base layer is formed by the method represented by step S13 and step S23 of the manufacturing method of the interference filter 1 of this embodiment, no turbid area is observed on the chip substrate, thereby confirming that the aggregation of the silver alloy is suppressed.

[0092] Next, the surface roughness of the base layer when the film thickness of the base layer is changed when a TiO 2 film is formed by the base step (step S13 , step S23 ) of this embodiment is described.

[0093] Figure 6 This is a graph showing the maximum surface height Rz of a 2 μm square relative to the film thickness of the base layer. Figure 7 The maximum surface height Rz of a 5 μm square relative to the film thickness of the base layer is shown in FIG. Specifically, a 2 μm square measurement was performed using an atomic force microscope (Park NX20 manufactured by ParkSystem) in SPM mode (see FIG. Figure 6 ) and 5μm square measurements (refer to Figure 7 ).

[0094] like Figure 6 as well as Figure 7 As shown, when the base layer is 5 nm thick, the maximum surface height Rz in a 2 μm square is 7.3 nm, and in a 5 μm square is 9.9 nm. If the base layer thickness is further increased, the maximum surface height Rz saturates and approaches a constant value.

[0095] As described above, when the maximum surface height Rz of the base layer (first base layer 21 and second base layer 22) within a 2-μm square is 7.3 nm or greater, and the maximum surface height Rz within a 5-μm square is 9.9 nm or greater, degradation of the reflective film can be suppressed even in a heated environment. On the other hand, if the base layer thickness is less than 5 nm, the surface roughness decreases, reducing the effectiveness of suppressing the aggregation of the reflective film. Therefore, in the interference filter 1 of this embodiment, the first base layer 21 and the second base layer 22 are formed to have a thickness of at least 5 nm and a maximum height roughness Rz of 7.3 nm or greater.

[0096] Next, the transmittance of the interference filter 1 according to the present embodiment after heating will be described.

[0097] Figure 8 Graphs showing transmittance before heating and transmittance after heating to 400° C. of the interference filter 1 according to the present embodiment. Figure 9Graphs showing transmittance before heating and transmittance after heating to 400° C. of an interference filter according to a comparative example.

[0098] Here, the interference filter of the comparative example does not have the first base layer 21 and the second base layer 22 of the interference filter 1 of this embodiment. Instead, a first reflective film 31 is formed on the first substrate 11 and covered with a protective film composed of IGO. Similarly, a second reflective film 32 is formed on the second substrate 12 and covered with a protective film composed of IGO.

[0099] like Figure 9 As shown in the figure, the transmittance of the comparative interference filter after heating is approximately 15% lower than the transmittance before heating. In this case, even though the protective film suppresses the aggregation of the silver or silver alloy constituting the reflective film, the transmittance is still reduced by approximately 15%. Furthermore, the protective film reduces the distance between adjacent peaks in the interference filter. Therefore, even when light of a desired wavelength is intended to pass through the interference filter, light from adjacent peaks is mixed in, thereby reducing the performance of the interference filter.

[0100] If a protective film is not formed on the interference filter, the reflective film may become cloudy due to aggregation of silver or silver alloy in a high-temperature usage environment, significantly reducing or even rendering the interference filter inoperable.

[0101] In contrast, in this embodiment, Figure 8 As shown, for at least the wavelength region of 600 nm and above, a decrease in transmittance is suppressed before and after heating. Specifically, when the distance between the first reflective film 31 and the second reflective film 32 is set so that light with a peak wavelength of 600 nm or above is transmitted through the interference filter 1, the transmittance of light at that peak wavelength is suppressed to less than 15% before and after heating, thereby maintaining the optical characteristics of the interference filter 1 before and after heating. Furthermore, in this embodiment, even without providing a protective film, the base layer suppresses aggregation of the silver or silver alloy constituting the reflective film, thereby maintaining high optical characteristics.

[0102] In addition, although the above example is an example of using a TiO2 layer as the base layer (the first base layer 21 and the second base layer 22), the same effect can be confirmed in Nb2O5, Ta2O5, HfO2, ZrO2, ITO, and IGO.

[0103] also, Figure 10The following is an example of a binary image obtained by heating the interference filter 1 of this embodiment to 400°C, photographing the reflective films (the first reflective film 31 and the second reflective film 32), and binarizing the photographed image using a predetermined threshold value. Specifically, the following is an example of an image obtained by photographing an observation image of the reflective film under an optical microscope, detecting the pixels with the highest brightness and the pixels with the lowest brightness in the photographed image, and binarizing the photographed image using the average brightness of these pixels as a threshold value. Figure 10 In the image, the black portion is a low-brightness pixel below the threshold, and the white portion is a pixel exceeding the threshold.

[0104] When the thickness of the base layer (the first base layer 21 and the second base layer 22) is set to 5 nm, images of multiple portions of the reflective film (the first reflective film 31 and the second reflective film 32) are captured and generated. Figure 10 In such a binarized image, the area ratio of pixels with brightness below the threshold, i.e., low-brightness pixels, is 10.93%. As mentioned above, if the thickness of the base layer is increased, the maximum surface height Rz value will be further increased, thereby further suppressing the aggregation of silver or silver alloys. As a result, the area ratio of low-brightness pixels in the binarized image is further reduced to 10.93%.

[0105] As described above, in the interference filter 1 comprising a silver or silver alloy reflective film (first reflective film 31, second reflective film 32) formed on substrates (first substrate 11, second substrate 12) via base layers (first base layer 21, second base layer 22) having a maximum height roughness Rz of 7.3 nm or greater, aggregation of the silver or silver alloy in the reflective film is suppressed even under a heated environment, resulting in an area ratio of 10.93% or less in a binary image. Consequently, even after heating, the decrease in transmittance is suppressed to less than 15% for at least a wavelength range of 600 nm or greater, thereby providing an interference filter 1 that maintains high optical characteristics.

[0106] Effects of this embodiment

[0107] The interference filter 1 of this embodiment includes: a first substrate 11; a second substrate 12 disposed opposite the first substrate 11 with a gap therebetween; a first base layer 21 disposed on the first surface 11A of the first substrate 11; a second base layer 22 disposed on the third surface 12A of the second substrate 12; a first reflective film 31 disposed on the first substrate 11 with the first base layer 21 interposed therebetween and made of silver or a silver alloy; and a second reflective film 32 disposed on the second substrate 12 with the second base layer 22 interposed therebetween and made of silver or a silver alloy. The first and second base layers 21 and 22 are each formed to have a maximum height roughness of 7.3 nm or greater.

[0108] In such an interference filter 1, even when used in a high-temperature environment or when heated during manufacturing, for example, when exposed to a high temperature of 400°C or higher, the base layer (first base layer 21, second base layer 22) suppresses aggregation of silver or silver alloy constituting the reflective film (first reflective film 31, second reflective film 32), thereby maintaining high optical characteristics.

[0109] Furthermore, compared to the case where other protective films are provided, optical properties (transmittance, reflectivity) are improved, and even in high-temperature environments, degradation of optical properties is suppressed. Furthermore, compared to the case where other protective films are provided, the peak wavelength interval of light passing through the interference filter 1 can be widened, and the problem of light of adjacent peak wavelengths mixing can be suppressed.

[0110] In the interference filter 1 of this embodiment, the area ratio of the low-brightness region in the binarized image obtained by capturing the reflective films (the first reflective film 31 and the second reflective film 32) is less than 10.93%. This improves the optical characteristics of the interference filter 1 and suppresses degradation of the optical characteristics even at elevated temperatures.

[0111] In the interference filter 1 of this embodiment, when the distance between the first reflective film 31 and the second reflective film 32 is set so that any peak wavelength within a wavelength range of 600 nm or greater is transmitted due to multiple reflections by the first reflective film 31 and the second reflective film 32, the change in the transmittance of light at the peak wavelength before and after heating is less than 15%.

[0112] Therefore, even when the interference filter 1 is exposed to a high-temperature environment, high optical characteristics can be maintained.

[0113] In the interference filter 1 of the present embodiment, the first substrate 11 and the second substrate 12 are made of any one of quartz, alkali-free glass, and borosilicate glass.

[0114] By using quartz, alkali-free glass, or borosilicate glass for the first substrate 11 or the second substrate 12 , it is possible to provide the interference filter 1 that uses the visible light region as the wavelength region to be spectrographed.

[0115] In the interference filter 1 of the present embodiment, the first underlayer 21 and the second underlayer 22 are made of any one of TiO 2 , Nb 2 O 5 , Ta 2 O 5 , HfO 2 , ZrO 2 , ITO, and IGO.

[0116] By using such a raw material, the first underlayer 21 and the second underlayer 22 having a maximum height roughness Rz of 7.3 nm can be easily formed by sputtering without requiring other steps such as surface treatment.

[0117] In the interference filter 1 of the present embodiment, the first reflection film 31 and the second reflection film 32 are made of a silver alloy, and are either Ag—Bi—Nd or Ag—Sm—Cu.

[0118] When silver is used as the first reflective film 31 and the second reflective film 32, degradation due to oxidation etc. tends to occur. In contrast, when either Ag-Bi-Nd or Ag-Sm-Cu is used, degradation of the reflective film can be suppressed.

[0119] The interference filter 1 of this embodiment includes: a base process (step S13, step S23), which forms a base layer on a substrate by sputtering; and a reflective film process (step S14, step S24), which forms a reflective film on the base layer. In the base process, the base layer is formed in such a manner that the maximum height roughness Rz of the base layer becomes greater than 7.3 nm.

[0120] As described above, even when exposed to a high temperature environment or a high temperature of, for example, 400° C. or higher during heating during manufacturing, aggregation of silver or silver alloy constituting the reflective film is suppressed, thereby enabling the manufacture of an interference filter 1 that maintains high optical characteristics.

[0121] In this embodiment, in the base process, TiO2 used as a base layer and a substrate are placed in a chamber in a vacuum state, and an inert gas and O2 are introduced into the chamber in a manner such that the amount of O2 relative to the inert gas becomes 1 / 9 or more, and a voltage is applied with TiO2 as a cathode and the substrate as an anode, thereby forming a film of TiO2 as a base layer on the substrate.

[0122] Thus, a base layer having a maximum height roughness Rz of 7.3 nm or more can be easily formed by sputtering, and surface treatment such as sandblasting can be eliminated.

[0123] Modification

[0124] The present invention is not limited to the above-described embodiment, and modifications and improvements within the scope of achieving the object of the present invention are encompassed by the present invention.

[0125] For example, in the first embodiment, the first base layer 21 is provided only on a portion of the first substrate 11 and the second base layer 22 is provided only on a portion of the second substrate 12 , but the present invention is not limited thereto.

[0126] Figure 11 1 is a schematic cross-sectional view of an interference filter 1A according to a modified example.

[0127] For example, Figure 11 As shown, the first base layer 21 may be formed entirely on the first surface 11A of the first substrate 11 , and the second base layer 22 may be formed entirely on the third surface 12A of the second substrate 12 .

[0128] In this case, the step of patterning the first base layer 21 or the second base layer 22 by etching or the like can be omitted.

[0129] Summary of the Disclosure

[0130] The optical filter of the first embodiment of the present invention comprises: a first substrate; a second substrate, which is opposite to the first substrate with a gap therebetween; a first base layer, which is arranged on the surface of the first substrate opposite to the second substrate; a second base layer, which is arranged on the surface of the second substrate opposite to the first substrate; a first reflective film, which is arranged on the first substrate with the first base layer therebetween and is composed of silver or a silver alloy; a second reflective film, which is arranged on the second substrate with the second base layer therebetween and is composed of silver or a silver alloy, and the maximum height roughness of the first base layer and the second base layer is not less than 7.3 nm.

[0131] In such an optical filter, even when used in a high-temperature environment or exposed to temperatures exceeding 400°C during heating during manufacturing, the base layers (first base layer, second base layer) can suppress aggregation of the silver or silver alloy constituting the reflective films (first reflective film, second reflective film), thereby maintaining high optical properties. Furthermore, by forming the reflective films on the base layers, optical properties (transmittance, reflectance) are improved.

[0132] In the optical filter of this method, in the captured image obtained by photographing the first reflective film and the second reflective film, the middle brightness which is the average brightness of the pixel with the lowest brightness and the pixel with the highest brightness is set as a threshold, and the area ratio of the low-brightness region with lower brightness when the captured image is binarized using the threshold is less than 10.93%.

[0133] This improves the optical characteristics of the optical filter and suppresses degradation of the optical characteristics even at elevated temperatures.

[0134] In the optical filter of this embodiment, when the distance between the first reflecting film and the second reflecting film is set so as to allow any peak wavelength in a wavelength range of 600 nm or more to be transmitted through multiple reflections performed by the first reflecting film and the second reflecting film, the change in the transmittance of light at the peak wavelength caused by heating the first reflecting film and the second reflecting film is less than 15%.

[0135] Therefore, even when the optical filter is exposed to a high-temperature environment, high optical characteristics can be maintained.

[0136] In the optical filter of this aspect, the first substrate and the second substrate are made of any one of quartz, alkali-free glass, and borosilicate glass.

[0137] This makes it possible to provide an optical filter that uses the visible light region as a wavelength region for spectroscopy.

[0138] In the optical filter of this embodiment, the first base layer and the second base layer are any one of TiO2, Nb2O5, Ta2O5, HfO2, ZrO2, ITO, and IGO.

[0139] By using such a raw material, the first and second underlayers having a maximum height roughness Rz of 7.3 nm can be easily formed by sputtering without requiring additional steps such as surface treatment.

[0140] In the optical filter of this aspect, the first reflective film and the second reflective film are made of a silver alloy, and are either Ag—Bi—Nd or Ag—Sm—Cu.

[0141] This can suppress degradation of the first reflective film or the second reflective film due to oxidation or the like.

[0142] The second embodiment of the present invention provides a method for manufacturing an optical filter, comprising a substrate, a base layer provided on the substrate, and a reflective film composed of silver or a silver alloy provided on the substrate via the base layer. The method comprises: a base process for forming the base layer on the substrate by sputtering; and a reflective film process for forming the reflective film on the base layer. In the base process, the base layer is formed in such a manner that the maximum height roughness of the base layer becomes greater than 7.3 nm.

[0143] Thus, an optical filter of the first type described above can be manufactured, and even when exposed to high temperatures, for example, above 400°C, in a high-temperature operating environment or during heating during manufacturing, the aggregation of silver or silver alloy constituting the reflective film can be suppressed, thereby manufacturing an optical filter that maintains relatively high optical properties.

[0144] In the manufacturing method of the optical filter of this embodiment, in the base process, the TiO2 used as the base layer and the substrate are placed in a chamber in a vacuum state, and an inert gas and O2 are introduced into the chamber in a manner such that the amount of O2 relative to the inert gas becomes 1 / 9 or more, and the TiO2 is set as a cathode and the substrate is set as an anode to apply a voltage, thereby forming a film of the TiO2 as the base layer on the substrate.

[0145] Thus, a base layer having a maximum height roughness Rz of 7.3 nm or more can be easily formed by sputtering, and surface treatment such as sandblasting can be eliminated.

[0146] Explanation of symbols

[0147] 1. 1A…interference filter; 11…first substrate; 11A…first surface; 11B…second surface; 12…second substrate; 12A…third surface; 13…bonding film; 21…first base layer; 22…second base layer; 31…first reflective film; 32…second reflective film; 41…first drive electrode; 42…second drive electrode; 51…first detection electrode; 52…second detection electrode; 111…groove; 112…movable portion; 113…diaphragm portion; 114…peripheral base portion; 121…recessed portion; 122…protrusion; 123…substrate bonding portion.

Claims

1. An optical filter comprising: a first substrate; a second substrate facing the first substrate with a gap therebetween; a first base layer provided on a surface of the first substrate opposite to the second substrate; a second base layer provided on a surface of the second substrate opposite to the first substrate; a first reflective film provided on the first substrate via the first base layer and made of silver or a silver alloy; a second reflective film provided on the second substrate via the second base layer and made of silver or a silver alloy; The maximum height roughness of the first base layer and the second base layer is greater than or equal to 7.3 nm.

2. The optical filter according to claim 1, wherein In the captured images obtained by photographing the first reflective film and the second reflective film, the area ratio of the low-brightness region with low brightness when binarizing the captured images using the threshold value, which is the average brightness of the pixel with the lowest brightness and the pixel with the highest brightness, is less than 10.93%.

3. The optical filter according to claim 1, wherein When the distance between the first reflective film and the second reflective film is set so that any peak wavelength within a wavelength range of 600 nm or greater is transmitted due to multiple reflections by the first reflective film and the second reflective film, a change in the transmittance of light at the peak wavelength due to heating of the first reflective film and the second reflective film is less than 15%.

4. The optical filter according to claim 1, wherein The first substrate and the second substrate are made of any one of quartz, alkali-free glass, and borosilicate glass.

5. The optical filter according to claim 1, wherein The first base layer and the second base layer are any one of TiO2, Nb2O5, Ta2O5, HfO2, ZrO2, ITO, and IGO.

6. The optical filter according to claim 1, wherein The first reflective film and the second reflective film are made of a silver alloy, and are made of any one of Ag—Bi—Nd and Ag—Sm—Cu.

7. A method for manufacturing an optical filter, the optical filter comprising: a substrate, an underlayer provided on the substrate, and a reflective film composed of silver or a silver alloy provided on the substrate via the underlayer, the method comprising: a base step of forming the base layer on the substrate by sputtering; a reflective film step of forming the reflective film on the base layer, In the base step, the base layer is formed so that the maximum height roughness of the base layer becomes 7.3 nm or more.

8. The method for manufacturing an optical filter according to claim 7, wherein: In the base process, the TiO2 used as the base layer and the substrate are placed in a chamber in a vacuum state, and an inert gas and O2 are introduced into the chamber in a manner such that the amount of O2 relative to the inert gas becomes 1 / 9 or more, and a voltage is applied by setting the TiO2 as a cathode and the substrate as an anode, so that the TiO2 is formed as a film on the substrate as the base layer.

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