JP5136250B2 - Manufacturing method of optical filter - Google Patents

Description

The present invention relates to an optical component that transmits light or prevents reflection of light, for example, a band limiting filter used in a photographing camera, a window (optical window) that transmits incident light, and a method for manufacturing an optical component such as a lens.

  In a light emitting device, a light receiving device, a photographing device, or the like, an optical component (for example, an optical filter) is required to exhibit a high transmittance with respect to light transmitted through the optical component. Therefore, a material having a low absorptance with respect to light in a target wavelength region is generally selected as a material constituting the optical component. Further, the loss of transmittance generated on the surface (incident surface and transmission surface) of the optical component based on the difference between the refractive index of the material constituting the optical component and the refractive index of the medium (usually air) in contact with the optical component. In order to reduce this, an antireflection film may be provided on the surface of the optical component.

  For example, in the conventional infrared optical filter, Ge, ZnS, ZnSe, Si, or the like is often used as a window material of the optical filter, and a metal fluoride or the like is employed as an antireflection film (for example, patents). Reference 3).

  Also, instead of forming an antireflection film on the surface of the optical component, the surface of the optical component is antireflective by microfabricating a regular three-dimensional structure with a space smaller than the wavelength of light on the surface. There have been attempts to provide functions (see, for example, Patent Documents 1 and 2 and Non-Patent Document 1).

JP 2002-287370 A JP-T-2004-521329 JP 2003-177210 A OPTICS LETTERS, Vol. 24, No. 20, October 15, p1422 (Optical Society of America)

  In recent years, there has been an increasing demand for higher functionality and higher efficiency of imaging devices, and in order to answer this, it has become necessary to make the optical wavelength band handled by imaging devices multiband. However, when the multilayer antireflection film as described above is applied to an optical component, the refractive index of the film or the linear expansion of the film is taken into consideration in the environment (for example, high temperature, heat cycle) in which the optical component is used. It was necessary to select the material of the film in consideration of material characteristics such as coefficient. That is, when used in an environment that exceeds the design specifications, phenomena such as peeling of the antireflection film, residual distortion, and release of residual gas from the antireflection film may hinder long-term reliability. In addition, when the band pass filter has a steep wavelength selectivity, the number of layers further increases, and there is a problem that the use environment is restricted due to the problem of the material selection.

  On the other hand, in a structure in which fine irregularities are formed on the surface of an optical component as shown in Patent Document 1 and an antireflection effect is aimed, it is required to select a desired wavelength band with a steep wavelength selectivity. It was particularly difficult to obtain a multiband optical filter.

The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a method for manufacturing an optical filter having excellent wavelength selectivity and excellent reliability.

The method of manufacturing an optical filter according to the present invention includes a group of a plurality of holes having a predetermined depth from the main surface of the substrate with an aperture diameter smaller than the wavelength λ of light targeted by the optical filter. The first step of digging a plurality of groups for each depth and the aperture diameter smaller than the wavelength λ of the light targeted by the optical filter include a plurality of holes when the main surface is viewed in plan, and the main surface is viewed in plan A second step of digging a hole having a large diameter shallower than the depth of the hole included in the substrate into the substrate, and an area occupied by the hole or the large diameter hole at a predetermined depth and a hole other than the hole or the large diameter hole The ratio with the remaining area of the substrate is a predetermined ratio for each depth.

  According to the present invention, a three-dimensional structure having a multilayer structure on the surface of the substrate can obtain desired transmittance characteristics by setting the filling rate of the structure in each layer and the thickness of each layer to predetermined values. it can. Moreover, there is no problem such as peeling due to the multilayer laminated film, and an optical filter having excellent reliability and excellent wavelength selectivity can be obtained.

Embodiment 1 FIG.
FIG. 1 is a perspective view showing a schematic configuration of an optical filter 10 according to the first embodiment. FIG. 2 is a schematic view of FIG. 1 shown in a perspective view in plan view. FIG. 3 is a schematic view of a cross section of the optical filter taken along the line III-III shown in FIG.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings, taking an optical filter for an infrared detector as an example. In the following description, the present invention will be described by taking a multiband optical filter corresponding to the 3-5 μm band and the 8-14 μm band as an example, but other forms are naturally included in the technical scope of the present invention. . It is also effective for light in other wavelength bands without being limited to the infrared wavelength band.

First, the overall configuration of the optical filter 1 will be described.
In FIG. 1, the optical filter 1 includes a lower small cylinder 31 and a large cylinder 4 disposed on a substrate 2, and an upper small cylinder 11 disposed on the large cylinder 4. The combination of these large and small cylinders will be referred to as the surface three-dimensional structure 3 for convenience. The material of the substrate 2 and the large cylinder 4 is Si that transmits infrared rays. In place of Si, Ge, ZnSe or a composite material thereof can be used as the substrate.

  With reference to FIG. 3, the surface three-dimensional structure 3 described above has a three-layer structure of a lower layer structure 30, a middle layer structure 20, and an upper layer structure 10 in order from the side closer to the substrate 2. Further, the surface three-dimensional structure 3 can be equivalently considered as a three-layer optical multilayer film in terms of optical characteristics. Hereinafter, the reason will be described.

First, considering the case where the surface three-dimensional structure 3 is a single layer, that is, a state in which only the lower small cylinder 31 is simply disposed on the substrate 2 (the state in which there is no large cylinder 4), refraction that determines the characteristics of the optical filter. It will be explained that the rate is determined by the shape of the surface three-dimensional structure.
When an optical component (here, an optical filter) is disposed in contact with a certain medium (usually air), all three-dimensional structures (here, lower layers) are used in order to prevent scattering of incident light on the light transmission surface. The distance L between the small cylinders 31) is designed to be equal to or smaller than the wavelength of the incident light. In such a three-dimensional structure, the area ratio between the concave portion and the convex portion (here, the area of the upper bottom surface of the lower small cylinder 31 is the area of the convex portion, and the portion not occupied by the lower small cylinder 31 on the substrate 2) Is considered as the area of the recess), the effective refractive index (n _x ) of the layer can be controlled. When the area ratio of the concave portion filled with air of the substrate 2 is set to f (when all concave portions are set to f = 1), the effective refractive index (n _x ) of this single layer is expressed by the formula ( It can be obtained from 1).

As described above, since the refractive index of a single layer can be calculated according to the equation (1), in the case of a three-layer surface three-dimensional structure 3, the refractive index is calculated for each layer of the upper layer to the lower layer structure. Can do. When applied to the three-dimensional structure as shown in FIG. 3, a three-layer structure in which the area ratio f is f ₁ , f ₂ , f ₃ from the upper layer can be obtained. The effective refractive index (n _x ) in this case is n ₁ , n ₂ , and n ₃ depending on each layer. As described above, by changing the area ratio f, it is possible to obtain the same effect as in the case of stacking multilayer films whose refractive indexes change stepwise. In addition, since the effective refractive index (n _x ) is determined by the area ratio f, for example, the lower small cylinders 31 may be arranged at random, and it is not particularly necessary that the uneven portion has a periodic structure.

Next, the wavelength peak of the single layer described above is determined from the formula (2) by the height of the convex portion of the effective refractive index portion (that is, the depth of the concave portion: d).

Therefore, in order to calculate the target wavelength band in which infrared rays are desired to be transmitted, the refractive index (n _x ) is calculated for each layer structure using the above equation (1), and the wavelength band desired to be transmitted is adjusted to (2). The thickness (d _x ) of each layer structure of the upper layer to the lower layer structure can be obtained using the formula.

When designing an optical filter of a multi-band corresponding to the 3~5μm band and 8~14μm band, (1), (2) appropriate equation based on the refractive index _(n x), the thickness _{(d x)} Calculate and combine them, and verify whether the desired transmittance characteristics can be obtained by a normal optical multilayer film calculation method. For example, in the case of a three-layer structure as shown in FIG. 3, the area ratio between the concave portion and the convex portion is appropriately selected, and the effective refractive index n ₁ = 1.5, n ₂ = 2.0, n ₃ = 2. .5 and when the depth of the recess is d ₁ = 0.5 μm, d ₂ = 0.9 μm, and d ₃ = 0.25 μm, it is good in the two wavelength bands targeted for design as shown in FIG. It is possible to obtain transmission characteristics.

  Further, in the present embodiment, the shape of the convex portion is a columnar shape, but it is not particularly necessary to be a columnar shape, and there is no problem even if it is a shape such as a prism. Further, it has been found that the wavelength selectivity is improved by making the effective refractive index stepwise, and it is desirable that the variation in the area ratio of each step is small.

  Next, an example of a method for manufacturing the optical filter of the present invention will be described with reference to the drawings. The manufacturing method described here is merely an example, and the above-described structure can be realized by other manufacturing methods.

  A method for manufacturing the above-described three-dimensional structure in which the effective refractive index is controlled on the substrate 2 will be described. 5 to 9 are schematic cross-sectional views illustrating the manufacturing method according to the present embodiment in the order of steps. The cross-sectional position corresponds to the position along the line III-III shown in FIG. Hereinafter, it demonstrates in order of a process.

  In the first step shown in FIG. 5, a pattern of a photoresist 41 is formed on the substrate 2 and used as a mask.

  In the second step shown in FIG. 6, a predetermined depth is dug by dry etching or the like.

  In the third step shown in FIG. 7, the photoresist 41 is temporarily removed and masked by the photoresist 42 so as to protect the deepest portion and dig the uppermost portion. Next, the surface layer portion is dug to a predetermined depth by dry etching or the like.

  In the fourth step shown in FIG. 8, the photoresist 42 is removed again and masked with the photoresist 43 so as to protect the outermost surface. In this state, the deepest convex portion is etched by dry etching or the like to be cut to a predetermined depth.

  Finally, the photoresist 43 is removed in a fifth step shown in FIG. The etching and exposure processes are repeated to realize an expected surface three-dimensional structure on the substrate surface.

Embodiment 2. FIG.
In the above-described first embodiment, the control example using the cylindrical projection is shown to realize the optical filter for infrared rays. However, the example has been described, but the surface three-dimensional structure is not necessarily a cylindrical projection. The area ratio f may be controlled by providing a large number of holes in the substrate for controlling the effective refractive index. FIG. 10 shows such a configuration, and is a perspective view showing a schematic configuration of the optical filter as in FIG. In the present embodiment, a cylindrical projection and a substrate are combined with a cylindrical hole. The same effect can be obtained by this configuration.

Embodiment 3 FIG.
In the second embodiment described above, the control example using the cylindrical protrusion is shown for realizing the optical filter. However, in the present embodiment, as shown in FIG. 11, the depth of the hole is different in three stages. The area ratio f is controlled by machining a hole in the substrate. The same effect can be obtained by this configuration.

Embodiment 4 FIG.
In the first embodiment described above, an example in which the effective refractive index (n _x ) is n ₁ <n ₂ <n ₃ from the outermost surface in order to realize the optical filter has been described. An optical filter can also be realized by producing a three-dimensional structure so that the distribution of n ₁ <n ₃ <n ₂ is satisfied. Hereinafter, the structure of this embodiment will be described. FIG. 13 is an exploded perspective view of the optical filter of the present embodiment for easy understanding of the structure, and is shown separated at the boundary between the third layer structure and the middle layer structure. Moreover, the schematic diagram of the cross section of an optical filter is shown in FIG.

  The structure of this embodiment will be described. The lower layer structure 30 is obtained by processing the surface of the substrate 2 and providing an intermediate cylinder. A thin Si substrate is used as the middle layer structure 20, and the upper layer structure 10 is formed by processing the surface of the Si substrate to form the upper layer small cylinder 11. The structure of this embodiment is a three-layer structure in which the bottom surface of the Si substrate (intermediate layer structure 20) is joined to the upper surface of the middle cylinder.

With this structure, the effective refractive index distribution described above can be realized. For example, as shown in FIG. 14, the effective refractive index n ₁ = 1.5, n ₂ = 2.5, n ₃ = 2.0 (= controlled from the area ratio) and the depth of the recess (d ₁ = 2. In the case of 0 μm, d ₂ = 0.6 μm, d ₃ = 0.7 μm), good transmission characteristics can be obtained in the two target wavelength bands.

  In the above-described embodiment 4, the lower layer structure is formed of a cylinder, but there is no problem even if the area ratio is controlled by another shape, and the same effect can be obtained with a prism, hexagonal hole, or groove.

Embodiment 5 FIG.
In the first embodiment described above, an example in which a fine pattern is formed by a photoresist pattern forming method using a lithography technique generally used in the semiconductor industry has been described. An example in which a microstructure is created by a so-called top-down approach has been shown.
In the fifth embodiment, an example in which a microstructure is created by a method using self-organization in which a nanoscale structure is spontaneously formed under a certain condition, that is, a so-called bottom-up approach. Will be explained.
This embodiment is described in, for example, “Fabrication of nanohole array on Si using self-organized porous alumina mask (J. Vac. Sci. Technol. B 19 (5), Sep / Oct 190,” 190/2001). The self-organizing properties of alumina, in which a regular array of pores with a nanometer period is naturally formed in a honeycomb shape, is used for manufacturing an optical filter.

  FIG. 15 is a schematic view showing a manufacturing process flow of the optical filter according to the present embodiment. FIG. 16 is a perspective view of an optical filter manufactured by the manufacturing process according to the present embodiment. Note that the dotted line figures shown in FIG. 16 are schematically shown through various holes excavated in the silicon substrate 76. FIG. 17 is a schematic view of FIG. 16 shown in a perspective view in plan view. FIG. 18 is a cross-sectional view of the optical filter. The cross-sectional position corresponds to the position along the line XVIII-XVIII shown in FIG. 19 to 30 are schematic cross-sectional views illustrating the manufacturing method according to the embodiment in the order of steps.

First, the process flow of this embodiment will be outlined.
Referring to FIG. 15 showing the process flow and FIG. 16 showing the structure of the optical filter, the upper layer structure 10 is manufactured in the first first step, and the lower layer structure 30 is manufactured in the subsequent second step. Finally, the intermediate layer structure 20 is produced in the third step, and the production of the optical filter is completed.

Hereinafter, the process flow will be described in detail in the order of steps.
At the beginning of the first step, aluminum is deposited by a method such as vapor deposition. This state is the aluminum 70 shown in FIG. The aluminum 70 functions as a mask for forming the small cylindrical hole 78 in the silicon substrate 76 in the subsequent process.

  Next, a description will be given of an alumina mask using the self-organization characteristics of alumina inquired in the above-mentioned literature. When the silicon substrate 76 on which the aluminum 70 shown in FIG. 19 is formed is anodized in an electrolyte such as phosphoric acid, oxalic acid, or sulfuric acid, alumina 71 having nano-sized pores 77 is formed on the silicon substrate 76. It begins to be formed on the aluminum film surface side. This state is the state shown in FIG. When the anodic oxidation is continued while energization is continued, the reaction end point where the deposited aluminum 70 is almost consumed and becomes the alumina 71 as shown in FIG. 21 is reached. The end point of the anodic oxidation reaction can be determined by monitoring the energized current. That is, while the aluminum 70 is consumed and the alumina 71 is formed, a steady current flows. However, when the aluminum 70 is almost consumed and the alumina 71 cannot be formed, the current does not flow rapidly. Therefore, when the current supply is stopped when the current drops below a certain threshold after the steady current flows, the barrier layer 80 made of thin alumina remains at the interface between the alumina 71 and the silicon substrate 2. A layer of alumina 71 having a large number of nano-sized pores 77 can be formed. This state is the state shown in FIG.

Next, when the barrier layer 80 is removed by immersion in a phosphoric acid solution, the state shown in FIG. 22 is obtained. Further, using the formed alumina 71 as a mask, the silicon substrate 76 is etched by RIE (Reactive Ion Etching) using CF 4 gas or the like to open nano-sized small cylindrical holes 78 in the silicon substrate 76. This state is the state shown in FIG.
Here, RIE using CF4 is taken as an example, but the small cylindrical hole 78 may be formed by IBE (ion beam etching) using Ar gas or the like, or ICP (Inductively Coupled Plasma) etching using C4F8 gas or the like. This is the first step for producing the upper layer structure 10.

  Next, the second step for forming the lower layer structure 30 will be described. First, in order to mask a region other than a portion where the lower layer structure 30 is to be formed, a photoresist pattern 72 using a lithography technique is formed. This state is the state shown in FIG. Next, the silicon substrate 76 is etched by RIE or the like to deeply dig a small nano-sized cylindrical hole 78 partially. This state is the state shown in FIG.

  Next, after removing the resist with acetone or the like, polishing is performed by CMP (Chemical Mechanical Polishing) or the like to remove the alumina 71 from the silicon substrate 76 to expose the silicon surface on the surface. This state is the state shown in FIG. This is the second step for manufacturing the lower layer structure 30.

Next, the third step for forming the intermediate layer structure 20 will be described.
First, the silicon substrate 76 is thermally oxidized in a thermal oxidation furnace. This state is the state shown in FIG. The thermal oxide film 75 shown in FIG. 27 functions as a mask for preventing the small cylindrical hole 78 forming the lower layer structure 30 from being etched when the intermediate layer structure 20 is formed.

  Next, the surface of the silicon substrate 76 is polished by CMP or the like, and the outermost thermal oxide film 75 is removed. This state is the state shown in FIG.

  Further, in order to form the intermediate layer structure 20, portions other than the region where the intermediate layer structure 20 is formed are masked with a resist pattern 73. This state is the state shown in FIG.

  Next, the exposed portion of the silicon substrate 76 that is not masked by the resist pattern 73 is etched by RIE to form a desired intermediate layer structure 20. This state is the state shown in FIG.

  Finally, the resist pattern 73 is removed with acetone or the like, and the thermal oxide film 75 is removed with HF or the like to complete the optical filter. The completed state is the state shown in FIG.

  When a fine structure is created by the so-called top-down approach as described in the first embodiment, an expensive process such as EB drawing is required, which is not suitable for mass production. However, when utilizing the self-organization characteristics of alumina described in the present embodiment, since it is originally a bottom-up method, it is easy to make a nano-sized structure, and expensive equipment is not required. There is an advantage that a complicated fine structure having a three-layer structure can be mass-produced at low cost.

  Further, in the optical filter manufacturing method described in the present embodiment, the filling rate of the structures in the upper layer, the middle layer, and the lower layer can be controlled under the conditions of aluminum anodization, so that desired transmittance characteristics can be easily obtained. . In addition, since the optical filter produced by such a manufacturing method is composed of a single structural material, there is no problem of peeling due to the multilayer laminated film, and an optical filter with excellent wavelength selectivity with excellent reliability is obtained. Can do. Furthermore, EB drawing is very expensive to draw a narrow area, and its use has been limited. However, if the self-organization characteristics of alumina are used, nano-sized structures are inexpensive in a wide area. Can be formed.

  In this embodiment, an alumina mask using the self-organization characteristics of alumina has been described. However, the present invention is not limited to the above-described embodiment, and the hole depth as shown in FIG. It can also be used in a staged structure. That is, first, a large number of small cylindrical holes 78 as shown in FIG. 23 are opened, and then the small cylindrical holes 78 are partially blocked by the resist pattern 73 as shown in FIGS. In this way, the desired upper layer structure 10, middle layer structure 20, and lower layer structure 30 may be formed separately.

Embodiment 6 FIG.
In the fifth embodiment, a nano-sized structure is formed by using the self-organization characteristics of alumina. However, the sixth embodiment is characterized in that a mask using nanoparticles is used. Nanoparticles made of silicon oxide dispersed in an organic solvent or water are applied to the silicon substrate, and the organic solvent or water is removed to leave only the nanoparticles made of silicon oxide on the silicon substrate, which is used as an etching mask. This method is used. For example, it is a method as referred to in Japanese Patent Application Publication No. 2007-250583. An example in which a fine structure is created by a bottom-up approach different from the above-described fifth embodiment will be described.

Hereinafter, the sixth embodiment will be described.
First, the process flow of the present embodiment will be described. Similar to the fifth embodiment described above, the upper layer structure 10 is first manufactured in the first step, and the lower layer structure 30 is manufactured in the subsequent second step. Finally, the intermediate layer structure 20 is produced in the third step, and the production of the optical filter is completed. FIG. 31 to FIG. 40 are schematic cross-sectional views showing the manufacturing method in the embodiment in the order of steps. The schematic cross-sectional view in the present embodiment is the same as that in the fifth embodiment.

Hereinafter, the process flow will be described in detail in the order of steps.
At the beginning of the first step, as a mask for forming the small holes 81 in the silicon substrate 76, nanoparticles 82 made of silicon oxide are formed by a method such as powder spray coating. This state is the state shown in FIG.

  Next, the silicon substrate 76 is etched by RIE or the like using the silicon oxide nanoparticles 82 as a mask, and nano-sized small holes 81 are formed in the silicon substrate 76. This state is the state shown in FIG. This is the first step for producing the upper layer structure 10.

  Next, the second step for forming the lower layer structure 30 will be described. First, in order to mask a region other than a portion where the lower layer structure 30 is to be formed, a photoresist pattern 72 is formed using a lithography technique. This state is the state shown in FIG. Next, the silicon substrate 76 is etched by RIE or the like to partially deepen the nano-sized small holes 81. This state is the state shown in FIG.

  Next, after removing the resist with acetone or the like, polishing is performed by CMP (Chemical Mechanical Polishing) or the like to remove the alumina 71 from the silicon substrate 76 to expose the silicon surface on the surface. This state is the state shown in FIG. This is the second step for manufacturing the lower layer structure 30.

Next, the third step for forming the intermediate layer structure 20 will be described.
First, the silicon substrate 76 is thermally oxidized in a thermal oxidation furnace. This state is the state shown in FIG. The thermal oxide film 75 shown in FIG. 36 functions as a mask for preventing the small holes 81 forming the lower layer structure 30 from being etched when the intermediate layer structure 20 is formed.
Next, the surface of the silicon substrate 76 is polished by CMP or the like, and the outermost thermal oxide film 75 is removed. This state is the state shown in FIG.
Further, in order to form the intermediate layer structure 20 by resist again, a photoresist pattern 73 using a lithography technique is formed in order to mask a region other than the portion where the intermediate layer structure 20 is to be formed. This state is the state shown in FIG.
Next, the exposed portion of the silicon substrate 76 that is not masked by the resist pattern 73 is etched by RIE to form a desired intermediate layer structure 20. This state is the state shown in FIG.
Finally, the resist pattern 73 is removed with acetone or the like, and the thermal oxide film 75 is removed with HF or the like to complete the optical filter. The completed state is the state shown in FIG.

  When a fine structure is created by the so-called top-down approach as described in the first embodiment, an expensive process such as EB drawing is required, which is not suitable for mass production. However, when utilizing the self-organization characteristics of the nanoparticles described in this embodiment, since it is originally a bottom-up method, it is easy to make a nano-sized structure, and effective equipment is not required. There is an advantage that a complicated fine structure having a three-layer structure can be mass-produced at low cost.

  Further, for example, in order to change the hole pitch, in the case of the anodic oxidation described in the fifth embodiment, it is necessary to control various conditions such as the selection of the electrolyte, the control of the liquid temperature and the current density. In the case of using particles, there is an advantage that a desired hole pitch can be obtained simply by selecting a liquid having a predetermined concentration in which particles of a desired size are dispersed.

  Further, in the optical filter manufacturing method described in the present embodiment, the filling rate of the structures in the upper layer, the middle layer, and the lower layer can be controlled by the size of the nanoparticles, so that desired transmittance characteristics can be easily obtained. In addition, since the optical filter produced by such a manufacturing method is composed of a single structural material, there is no problem of peeling due to the multilayer laminated film, and an optical filter with excellent wavelength selectivity with excellent reliability is obtained. Can do. Furthermore, EB drawing is very expensive for drawing a narrow area, and its use has been limited. However, if nanoparticle self-organization characteristics are used, nano-sized structures can be formed in a wide area. It can be formed at low cost.

  In addition, although the nanoparticle made from the silicon oxide was demonstrated to the example as a nanoparticle, the material used as a mask at the time of the etching of a silicon substrate can be used also for another nanoparticle. For example, alumina nanoparticles can be used.

  The above-described embodiment is an exemplification, and the present invention is not limited to the scope of the illustrated embodiment. For example, in the above-described embodiment, the example in which the concavo-convex shape is added to one main surface of the filter substrate has been described, but the filter substrate may be formed on the other main surface of the filter substrate. The present invention is defined by the terms of the claims, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

It is a perspective view of the optical filter of Embodiment 1 of the present invention. It is a top view of the optical filter of Embodiment 1 of the present invention. It is sectional drawing of the optical filter of Embodiment 1 of this invention. It is an example of the transmission characteristic of the optical filter of Embodiment 1 of this invention. It is sectional drawing in the manufacturing process of the optical filter of Embodiment 1 of this invention. It is sectional drawing in the manufacturing process of the optical filter of Embodiment 1 of this invention. It is sectional drawing in the manufacturing process of the optical filter of Embodiment 1 of this invention. It is sectional drawing in the manufacturing process of the optical filter of Embodiment 1 of this invention. It is sectional drawing in the manufacturing process of the optical filter of Embodiment 1 of this invention. It is a perspective view of the optical filter of Embodiment 2 of the present invention. It is a perspective view of the optical filter of Embodiment 3 of the present invention. It is sectional drawing of the optical filter of Embodiment 4 of this invention. It is a perspective view of the optical filter of Embodiment 4 of this invention. It is an example of the transmission characteristic of the optical filter of Embodiment 4 of this invention. It is a figure explaining the process flow of Embodiment 5 of this invention. It is a perspective view of the optical filter of Embodiment 5 of the present invention. It is a top view of the optical filter of Embodiment 5 of the present invention. It is sectional drawing of the optical filter of Embodiment 5 of this invention. It is sectional drawing in the manufacturing process of the optical filter of Embodiment 5 of this invention. It is sectional drawing in the manufacturing process of the optical filter of Embodiment 5 of this invention. It is sectional drawing in the manufacturing process of the optical filter of Embodiment 5 of this invention. It is sectional drawing in the manufacturing process of the optical filter of Embodiment 5 of this invention. It is sectional drawing in the manufacturing process of the optical filter of Embodiment 5 of this invention. It is sectional drawing in the manufacturing process of the optical filter of Embodiment 5 of this invention. It is sectional drawing in the manufacturing process of the optical filter of Embodiment 5 of this invention. It is sectional drawing in the manufacturing process of the optical filter of Embodiment 5 of this invention. It is sectional drawing in the manufacturing process of the optical filter of Embodiment 5 of this invention. It is sectional drawing in the manufacturing process of the optical filter of Embodiment 5 of this invention. It is sectional drawing in the manufacturing process of the optical filter of Embodiment 5 of this invention. It is sectional drawing in the manufacturing process of the optical filter of Embodiment 5 of this invention. It is sectional drawing in the manufacturing process of the optical filter of Embodiment 6 of this invention. It is sectional drawing in the manufacturing process of the optical filter of Embodiment 6 of this invention. It is sectional drawing in the manufacturing process of the optical filter of Embodiment 6 of this invention. It is sectional drawing in the manufacturing process of the optical filter of Embodiment 6 of this invention. It is sectional drawing in the manufacturing process of the optical filter of Embodiment 6 of this invention. It is sectional drawing in the manufacturing process of the optical filter of Embodiment 6 of this invention. It is sectional drawing in the manufacturing process of the optical filter of Embodiment 6 of this invention. It is sectional drawing in the manufacturing process of the optical filter of Embodiment 6 of this invention. It is sectional drawing in the manufacturing process of the optical filter of Embodiment 6 of this invention. It is sectional drawing in the manufacturing process of the optical filter of Embodiment 6 of this invention.

Explanation of symbols

1 optical filter,
2 substrates,
3 surface three-dimensional structure,
4 Large cylinder 10 Upper layer structure,
11 Upper small cylinder,
12 Etching hole 13 Upper layer substrate 20 Middle layer structure,
30 Underlayer structure,
31 Lower cylinder,
32 Etching hole 33 Etching groove 40 Photoresist 41 Photoresist 42 Photoresist 43 Photoresist 70 Aluminum 71 Alumina 72 Resist pattern 73 Resist pattern 75 Thermal oxide film 76 Silicon substrate 77 Pore 78 Small cylindrical hole 79 Large cylindrical hole 80 Barrier layer 81 Small hole 82 nanoparticles

Claims (2)

A plurality of groups of holes each having a predetermined depth from the main surface of the substrate with a diameter smaller than the wavelength λ of light targeted by the optical filter is dug into the substrate of the optical filter. 1 process,
The optical filter has an aperture diameter smaller than the wavelength λ of the target light , includes a plurality of the holes when the main surface is viewed in plan, and is deeper than the depth of the hole included when the main surface is viewed in plan A second step of digging a shallow large-diameter hole into the substrate,
The ratio of the area occupied by the hole or the large-diameter hole at the predetermined depth to the area of the remaining area of the substrate other than the hole or the large-diameter hole is a predetermined ratio for each depth. An optical filter manufacturing method characterized by comprising: After the first step and before the second step, an intermediate step of forming a thermal oxide film on the inner wall of the hole by thermally oxidizing the substrate is provided,
In the first step, an aluminum layer is formed on the surface of the substrate of the optical filter, and an alumina layer having a plurality of openings in which the substrate is partially exposed is formed by anodizing the aluminum layer. Etching the substrate using the alumina layer as a mask to dig the hole in the main surface of the substrate,
2. The second step includes digging a large-diameter hole as a mask for preventing the hole included in the thermal oxide film from being etched when the main surface is viewed in plan. The manufacturing method of the optical filter as described in any one of.

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