Optical filter, photodiode module, and method for manufacturing optical filter

Abstract

To provide an optical filter which selectively transmits light of a wavelength of 280 nm or less, offers improved separation performance from light of a wavelength of approximately 300 nm or greater, and can be easily manufactured.SOLUTION: An optical filter provided herein comprises a transparent substrate and an aluminum-based film provided on the transparent substrate. The aluminum-based film has multiple holes arranged such that the inter-center distance between the adjacent holes is 200 nm or less. The transparent substrate has multiple cavities located directly below the holes of the aluminum-based film and formed to have a depth of 5 nm or greater relative to a surface of the transparent substrate.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to an optical filter, a photodiode module, and a method for manufacturing an optical filter. [Background technology]

[0002] Demand for semiconductor light receiving elements for light with wavelengths of 280 nm or less (also called deep ultraviolet light or UV-C) has been increasing in recent years. Applications include flame sensors for fire detection (reference: flames generally include UV-C) and sterilization monitors (reference: UV-C is considered to have a sterilizing effect). In particular, there is a high demand for flame sensors as small sensors for security purposes.

[0003] The important practical performance of the above-mentioned semiconductor light receiving element is the ability to separate from the solar spectrum including light around 300 nm, and therefore it is required to increase the rejection ratio, which indicates the index of UV-C sensitivity. Against this background, research on semiconductor structures has been actively conducted (Non-Patent Document 1).

[0004] In addition, there is a method of combining a transmission filter with a technology for improving the light receiving sensitivity of a semiconductor light receiving element, and many methods using a dielectric multilayer film as such a filter have been proposed (Patent Documents 1 and 2). However, in such a filter, if narrowband characteristics are required, it becomes necessary to increase the number of layers, and such multilayering is not productive.

[0005] Patent Document 3 discloses a filter in which openings are periodically provided in a metal thin film. This is a transmission filter in which openings smaller than the wavelength are provided in a conductive material thin film, and light propagated by an extraordinary transmission phenomenon caused by surface plasmons is utilized. Details of the principle of such a transmission filter are described in Non-Patent Document 2. In addition, the transmission characteristics of the filter are also affected by the optical constants of the material surrounding the openings, and as described in Non-Patent Document 2, for example, when the substrate of the aluminum film is a silica substrate, there are two transmission peaks (main peak and sub-peak) due to resonance between the opening and the space side, and resonance between the opening and the silica side. It is also described that the intensity of these peaks changes when a silica film is formed on the aluminum film.

[0006] On the other hand, as a technique for removing the above-mentioned sub-peaks and transmitting only the desired wavelength range, Patent Document 4 describes a laminated structure of an aperture. Also, Non-Patent Document 3 realizes a narrow-band filter by increasing the number of layers of a metal mesh filter and providing a hollow portion. However, although these conventional techniques are devised to adjust or remove the sub-peaks, such structures are complicated. [Prior art documents] [Non-patent literature]

[0007] [Non-Patent Document 1] "Development of Highly Sensitive Deep UV Sensors - From Photomultiplier Tubes to Solid-State Devices" by Yo Yoshikawa et al., OPTRONICS, 2020 [Non-Patent Document 2] Jinlian Hu et al., Dual-channel extraordinary ultraviolet transmission through an aluminum nanohole array: Nanotechnology 28 215205 (2017) [Non-Patent Document 3] Takashi Uetsuka et al., Development of Highly Durable Metal Mesh Filter for Long and Mid-Infrared, 3rd Workshop on Visible and Infrared Observation Instruments, 2013 [Patent documents]

[0008] [Patent Document 1] JP 2006-080782 A [Patent Document 2] JP 2008-021460 A [Patent Document 3] Japanese Patent Application Publication No. 11-072607 [Patent Document 4] JP 2015-031856 A Summary of the Invention [Problem to be solved by the invention]

[0009] Therefore, the present invention aims to solve the above-mentioned problems in the prior art and to achieve the following object: That is, the present invention aims to provide an optical filter that selectively transmits light with a wavelength of 280 nm or less, has improved performance in separating light with a wavelength of approximately 300 nm or more, and can be easily manufactured. Another object of the present invention is to provide a photodiode module including the above-mentioned optical filter. Another object of the present invention is to provide a method for producing an optical filter, which can easily produce the above-mentioned optical filter. [Means for solving the problem]

[0010] The inventors of the present invention, keeping in mind that the degree of narrowband property may depend on the application, first focused on reducing the sub-peak (silica peak) of the two transmission peaks shown in Non-Patent Document 2. As a result of further intensive research, the inventors of the present invention found that it is possible to reduce the sub-peak located at a wavelength of about 300 nm or more and / or increase the main peak located at a wavelength of 280 nm or less by forming a cavity of a predetermined form by surface processing on the transparent substrate on which the aluminum film is disposed, and thus arrived at the present invention.

[0011] The means for achieving the above object are as follows.

[0012] <1> A transparent substrate and an aluminum-based film disposed on the transparent substrate, the aluminum-based film has a plurality of holes, the distance between the centers of adjacent holes being 200 nm or less; An optical filter, characterized in that the transparent substrate has a plurality of cavities directly below the holes in the aluminum-based film, and the depth of the cavities based on the surface of the transparent substrate is 5 nm or more.

[0013] <2> the holes in the aluminum-based film are circular in plan view, and the hole diameter on one film surface is different from the hole diameter on the other film surface; <1> The optical filter according to claim 1 .

[0014] <3> The aluminum-based film contains silicon (Si) or copper (Cu) at a ratio of 10 mass% or less. <1> or <2> The optical filter according to claim 1 .

[0015] <4> The material of the transparent substrate is quartz or sapphire. <1> ~ <3> 13. The optical filter according to any one of claims 1 to 12.

[0016] <5> a photodiode having a semiconductor layer on a substrate; <1> ~ <4> and an optical filter according to any one of claims 1 to 5.

[0017] <6> The optical filter is disposed in contact with a surface of the base material on which the semiconductor layer is not formed. <5> The photodiode module according to claim 1 .

[0018] <7> <1> ~ <4> A method for producing an optical filter according to any one of the above, a film forming step of forming an aluminum-based film having a plurality of holes on a transparent substrate; Thereafter, a substrate processing step of forming a plurality of cavities on the transparent substrate through the plurality of holes, In the film formation step, holes are patterned by self-organization of a block copolymer or by two-beam interference exposure; In the substrate processing step, plasma etching is performed. A method for producing an optical filter. Effect of the Invention

[0019] According to the present invention, it is possible to provide an optical filter that selectively transmits light with a wavelength of 280 nm or less while improving the performance of separating light with a wavelength of approximately 300 nm or more, and that can be easily manufactured. Furthermore, according to the present invention, it is possible to provide a photodiode module including the above-mentioned optical filter. Furthermore, according to the present invention, it is possible to provide a method for producing an optical filter, which can easily produce the above-mentioned optical filter. [Brief description of the drawings]

[0020] [Figure 1] 1 is a schematic plan view of an optical filter according to an embodiment of the present invention; [Diagram 2] 2 is a schematic cross-sectional view of the optical filter of FIG. 1 taken along line AA. [Diagram 3] FIG. 2 is a schematic plan view of an optical filter according to another embodiment of the present invention. [Figure 4] FIG. 11 is a schematic cross-sectional view of an optical filter according to yet another embodiment of the present invention. [Diagram 5]FIG. 11 is a schematic cross-sectional view of an optical filter according to yet another embodiment of the present invention. [Figure 6] FIG. 2 is a process flow diagram for explaining a method for manufacturing an optical filter according to an embodiment of the present invention. [Figure 7] 1 is a schematic side view of a photodiode module according to an embodiment of the present invention; [Figure 8] FIG. 11 is a diagram showing a comparison of transmission spectra with and without a cavity in this embodiment. [Figure 9] FIG. 11 is a diagram showing a comparison of transmission spectra according to hole pitch in the present embodiment. [Figure 10] FIG. 11 is a diagram showing a comparison of transmission spectra according to cavity depth in the present embodiment. [Figure 11] FIG. 11 is a diagram showing a comparison of transmittance at a specific wavelength depending on the cavity depth in this embodiment. [Figure 12] FIG. 11 is a diagram showing a comparison of transmission spectra with and without a cavity in this embodiment. [Figure 13] FIG. 11 is a diagram showing a comparison of transmission spectra with and without a cavity in this embodiment. [Figure 14] FIG. 11 is a diagram showing a comparison of transmission spectra with and without a cavity in this embodiment. [Figure 15] FIG. 11 is a diagram showing a comparison of transmission spectra depending on the hole size in this embodiment. [Figure 16] FIG. 13 is a diagram showing the transmission spectrum of a comparative optical filter having a metal film other than an aluminum-based film in the present embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] The present invention will be described in detail below based on the embodiments. Note that the drawings used in the description are shown to improve understanding of the invention, and the scale, dimensional relationship, shape, and other detailed structures of the components in each drawing may be different from the actual ones.

[0022] (Optical Filter) An optical filter according to one embodiment of the present invention (hereinafter, sometimes referred to as "the optical filter of this embodiment") has a basic structure including a transparent substrate and an aluminum-based film disposed on the transparent substrate. The optical filter of this embodiment is characterized in that the aluminum-based film has a plurality of holes, and the distance between the centers of adjacent holes (hereinafter, sometimes referred to as "hole pitch") is 200 nm or less, and that the transparent substrate has a plurality of cavities directly below the holes in the aluminum-based film, and the depth of the cavities based on the surface of the transparent substrate is 5 nm or more.

[0023] Fig. 1 shows a schematic plan view of the optical filter of this embodiment, and Fig. 2 shows a schematic cross-sectional view of the optical filter of Fig. 1 taken along line AA. As shown in Fig. 2 in particular, the optical filter 100 has a structure including at least a transparent substrate 11 and an aluminum-based film 21, with the aluminum-based film 21 disposed on the transparent substrate 11. Note that, in the optical filter 100, it is preferable that the transparent substrate 11 and the aluminum-based film 21 are in direct contact with each other, as shown in Fig. 2.

[0024] Furthermore, the optical filter 100 has a plurality of holes 22 (portions penetrating through the entire film thickness) formed in the aluminum-based film 21. In this manner, a structure in which a plurality of holes are formed in an aluminum-based film disposed on a transparent substrate can generally have a main peak on the low wavelength side and a sub-peak on the high wavelength side observed in the light transmission spectrum. Note that, for convenience of explanation, only four holes 22 are shown in FIG. 1 and the like, but typically, an infinite number of holes 22 are formed on the aluminum-based film 21.

[0025] The planar shape of the holes 22 is not particularly limited. For example, as shown in Fig. 1, the holes 22 may be circular (including a perfect circle or an ellipse), or may be polygonal (including a triangular or rectangular shape), or may be an unspecified random shape. Furthermore, the multiple holes 22 formed in one optical filter 100 may have the same or different planar shapes, and may have the same or different sizes (diameter, etc.) as each other.

[0026] Furthermore, the plurality of holes 22 formed in the aluminum-based film 21 may be arranged in a regular pattern or may be arranged randomly.

[0027] 2, the optical filter 100 has a plurality of cavities 12 (areas that do not penetrate the transparent substrate 11 but are hollow) formed in the transparent substrate 11 directly below the holes 22 formed in the aluminum-based film 21. For this reason, the optical filter 100 as a whole can be recognized as one cavity being composed of the holes 22 in the aluminum-based film 21 and the cavities 12 in the transparent substrate 11. Conventionally, filters formed by providing a plurality of openings in a metal film laminated on a substrate have been known, but the provision of cavities 12 in the substrate (transparent substrate 11) itself, as in the optical filter 100 of this embodiment, is at least considered to be novel.

[0028] In the optical filter 100 of this embodiment, the distance between the centers of adjacent holes 22 in the aluminum-based film 21, i.e., the hole pitch P1 also shown in FIG. 1, must be 200 nm or less. If there is a portion where the hole pitch P1 exceeds 200 nm, the position of the main peak in the light transmission spectrum shifts to the high wavelength side to around 300 nm, and a large amount of undesirable light such as sunlight is transmitted, resulting in a decrease in the separation performance with light having a wavelength of about 300 nm or more. In addition, from the viewpoint of further improving the separation performance with light having a wavelength of about 300 nm or more, the hole pitch P1 in the aluminum-based film 21 is preferably 180 nm or less. On the other hand, the hole pitch P1 in the aluminum-based film 21 is not particularly limited, but can be 120 nm or more. When the shape of the hole 22 in plan view is a shape other than a circle, the "center of the hole" is the center of gravity of the shape of the hole in plan view.

[0029] In addition, in Fig. 1, the pitch between two diagonal holes among four holes arranged to form a rectangle when their center points are connected is shown as P1, but this is merely the longest pitch shown as P1 in Fig. 1. That is, the optical filter of this embodiment requires that the center distance between any two arbitrarily selected adjacent holes is 200 nm or less.

[0030] Furthermore, in the optical filter 100 of this embodiment, the depth (D1 shown in FIG. 2) of the cavity 12 formed in the transparent substrate 11 is set to 5 nm or more when the surface of the transparent substrate 11 is used as a reference. This makes the main peak sharper (the half-width is smaller) and also reduces the height of the sub-peak. That is, in the optical filter 100 of this embodiment, the optimization of the hole pitch P1 described above and the optimization of the depth D1 of the cavity 12 formed in the transparent substrate 11 are combined to significantly increase the transmittance of light on the low wavelength side (wavelength of 280 nm or less) while decreasing the transmittance of light on the high wavelength side (wavelength of about 300 nm or more). Moreover, from the viewpoint of more sufficiently improving the separation performance with light having a wavelength of about 300 nm or more, the depth D1 of the cavity 12 is preferably 10 nm or more, more preferably 25 nm or more, even more preferably 50 nm or more, even more preferably 75 nm or more, and particularly preferably 100 nm or more. Further, the depth D1 of the cavity 12 is not particularly limited, but may be set to 150 nm or less from the viewpoints of the manufacturing process and productivity. In FIG. 2, each cavity 12 has a constant depth. However, if the depth is not constant, the depth of the deepest part is taken as the depth D1 of the cavity 12.

[0031] In the optical filter 100 of this embodiment, it is preferable that there is no step between the hole 22 and the cavity 12, and they smoothly communicate with each other, as shown in Fig. 2. In other words, in the optical filter 100 of this embodiment, it is preferable that the shape of the hole 22 in a plan view is substantially the same as the shape of the cavity 12 in a plan view.

[0032] The material of the transparent substrate 11 is not particularly limited as long as it has transparency, and examples thereof include inorganic materials, plastic materials, etc. Examples of inorganic materials include silica such as quartz, sapphire, diamond, etc. Among these, the material of the transparent substrate is preferably an inorganic material from the viewpoints of marketability, processability, stability, etc., more preferably quartz or sapphire, and even more preferably quartz.

[0033] The thickness of the transparent substrate 11 is not particularly limited, but from the viewpoints of ease of handling during production and mechanical stability, it is preferably 0.1 mm or more and 10 mm or less.

[0034] The aluminum-based film 21 is a film containing at least aluminum or an aluminum compound. The aluminum-based film 21 may also be an alloy. However, from the viewpoint of obtaining desired transmission characteristics, the ratio of aluminum or an aluminum compound in the aluminum-based film 21 is preferably 50 mass % or more, and more preferably 80 mass % or more.

[0035] The aluminum-based film 21 preferably contains silicon (Si) or copper (Cu) in a ratio of 10 mass % or less. By producing the aluminum-based film 21 by adding silicon (Si) or copper (Cu) to aluminum or an aluminum compound in the above-mentioned ratio, the grain size of the aluminum can be reduced, and it becomes easier to produce the aluminum-based film 21 having the desired shape (the configuration of the plurality of holes 22).

[0036] The thickness of the aluminum-based film 21 (T1 shown in FIG. 2) is not particularly limited, but from the viewpoint of obtaining a more sufficient filtering effect, it is preferably 50 nm or more, and from the viewpoint of productivity, it is preferably 100 nm or less.

[0037] The size of the hole 22 formed in the aluminum-based film 21 (W1 shown in FIG. 1) is not particularly limited, but from the viewpoint of ease of hole formation, it is preferably 20 nm or more, and from the viewpoint of further reducing the sub-peak height, it is preferably 120 nm or less, more preferably 100 nm or less, and even more preferably 80 nm or less. If the shape of the hole 22 in plan view is other than circular, the "hole size W1" is the longest length of the line segments connecting two points on the contour of the hole. In addition, in this specification, if the shape of the hole in plan view is circular, the hole size W1 may be referred to as the hole diameter φ1.

[0038] 3 is a schematic plan view of an optical filter according to another embodiment of the present invention. In the optical filter 100 of the present invention, the size W1 of the plurality of holes 22 in the aluminum-based film may be different, as shown in FIG.

[0039] FIG. 4 is a schematic cross-sectional view of an optical filter according to another embodiment of the present invention. In the optical filter 100 of the present invention, the holes 22 of the aluminum-based film 21 are circular in plan view, and as shown in FIG. 4, it is preferable that the hole diameter φ11 on one film surface of the aluminum-based film 21 is different from the hole diameter φ12 on the other film surface. In this case, when transmitting light with a wavelength of 280 nm or less, the separation performance from light with a wavelength of about 300 nm or more can be further improved. In addition, holes 22 with different hole diameters φ11 and φ12 are less difficult to manufacture than holes 22 with the same hole diameters φ11 and φ12. Furthermore, from the same viewpoint, it is preferable that the hole diameter φ11 on the outermost surface side of the aluminum-based film 21 is larger than the hole diameter φ12 on the transparent substrate 11 side.

[0040] Fig. 5 is a schematic cross-sectional view of an optical filter according to yet another embodiment of the present invention. In the optical filter 100 of the present invention, one or more metal films may be further disposed on the aluminum-based film 21, as shown in Fig. 5. In this case, a plurality of holes 22 are formed in the metal film at the same positions as the aluminum-based film 21.

[0041] In the optical filter 100 shown in FIG. 5, examples of the material for the first laminated film 31 formed directly on the aluminum-based film 21 include oxides such as silica and alumina, and fluorides such as magnesium fluoride. Examples of the material for the second laminated film 41 formed directly on the first laminated film 31 include gallium oxide (GaO 3 ), gallium nitride (GaN), etc. The thickness of each of these laminated films can be appropriately adjusted depending on the purpose.

[0042] (Method of manufacturing optical filters) The manufacturing method of an optical filter according to one embodiment of the present invention (hereinafter sometimes referred to as the "manufacturing method of this embodiment") is a method for manufacturing the above-mentioned optical filter, and includes a film formation step of forming an aluminum-based film having a plurality of holes on a transparent substrate, and then a substrate processing step of forming a plurality of cavities on the transparent substrate via the plurality of holes. The manufacturing method of this embodiment is characterized in that in the film formation step, holes are patterned by self-organization of a block copolymer or two-beam interference exposure, and in the substrate processing step, plasma etching is performed. According to this manufacturing method of this embodiment, the above-mentioned optical filter can be easily manufactured.

[0043] 6 is a process flow diagram illustrating an example of the production method of this embodiment, in which self-organization of a block copolymer is carried out in the film formation step.

[0044] <Film formation process> First, a transparent substrate 11 is prepared (FIG. 6(a)), and a neutral layer 51 is formed on this transparent substrate 11 (FIG. 6(b)). This neutral layer 51 can be formed as a random copolymer layer, for example, by applying a solution obtained by dissolving a random copolymer in a solvent and heating it. Note that this neutral layer 51 is formed for the purpose of improving the adhesion of a block copolymer, which will be described later, and is called "neutral" because phase separation does not occur as in block copolymers.

[0045] Next, a solution (diblock copolymer solution 52) obtained by dissolving a diblock copolymer in a solvent is applied onto the neutral layer 51 (FIG. 6(c)). After that, by heating the solution, the diblock copolymer is phase-separated and separated into polymer components on the substrate in a self-organizing manner, resulting in an arrangement of two polymers having periodicity. Furthermore, by utilizing the difference in etching resistance between the polymer components, the other polymer is removed by plasma etching or a chemical solution to form uneven surfaces, forming self-assembled dots 53 having a predetermined shape and arrangement pattern (FIG. 6(d)). The shape and arrangement pattern of the self-assembled dots 53 correspond to the shape and arrangement pattern of the holes in the final optical filter. At this time, the shape of the self-assembled dots 53 (and thus the shape of the holes in the final optical filter, the size W1 of the holes, the hole pitch P1, etc.) can be adjusted by appropriately changing the composition and molecular weight of the diblock copolymer used.

[0046] Next, the exposed neutral layer 51 is removed (FIG. 6(e)). Examples of the removal method include plasma treatment and wet etching using a solvent.

[0047] Next, an aluminum-based film 21 is formed on the exposed surface (FIG. 6(f)). Examples of a method for forming the aluminum-based film include a sputtering method and a vacuum deposition method. At this time, the thickness T1 of the aluminum-based film 21 can be adjusted by appropriately changing the formation conditions.

[0048] Next, the self-assembled dots 53 and the underlying neutral layer 51 are removed (FIG. 6(g)). As a result, the areas where the self-assembled dots 53 have been removed become holes 22. Examples of the removal method include a surface treatment using a solvent and a lift-off process using a solvent in combination.

[0049] <Substrate processing process> Next, the transparent substrate 11 is processed through the holes 22 formed in the film formation process (FIG. 6(h)). Plasma etching is used for this processing. As a result, a plurality of cavities 12 are formed in the transparent substrate 11 directly below the holes 22 formed in the aluminum-based film 21, and the optical filter 100 can be obtained. Note that the gas used for the plasma etching can be, for example, carbon tetrafluoride (CF 4 ), sulfur hexafluoride (SF 6 In addition, by appropriately changing the plasma etching conditions, the cavity depth D1 in the transparent substrate 11 can be adjusted.

[0050] In the above, self-assembled dots 53 having a predetermined shape and arrangement pattern are formed by self-organization of the block copolymer, and holes are patterned. Alternatively, however, something equivalent to the self-assembled dots 53 can be formed on the transparent substrate 11 by two-beam interference exposure.

[0051] (Photodiode module) A photodiode module according to one embodiment of the present invention is characterized in that it includes a photodiode having a semiconductor layer on a substrate and the above-mentioned optical filter. Since the photodiode module includes the above-mentioned optical filter, it can be used for various applications based on UV-C sensing.

[0052] The arrangement of each member in the photodiode module is not particularly limited. For example, the optical filter may be arranged so as to be in contact with the semiconductor layer on the substrate, or may be arranged apart from the substrate and the semiconductor layer (photodiode).

[0053] FIG. 7 is a schematic side view of a photodiode module according to an embodiment of the present invention. The photodiode module 300 in FIG. 7 includes a photodiode 200 in which a semiconductor layer 252 is formed on a substrate 251. An electrode 253 is disposed on the semiconductor layer 252. In the photodiode module 300 in FIG. 7, the optical filter 100 is disposed in contact with the surface of the substrate 251 on which the semiconductor layer 252 is not formed. Since the optical filter 100 can function even when directly formed on the substrate 251, the arrangement shown in FIG. 7 has the advantage of being applicable to various applications. For example, in a photodiode module 300 in which a sapphire substrate is used as the substrate 251 and an Mg-ZnO layer is formed as the semiconductor layer 252, the band gap can be controlled by adjusting the amount of Mg added to the Mg-ZnO layer.

[0054] In addition, the surface of optical filter 100 facing substrate 251 in the photodiode module is not particularly limited, and may be the surface on which an aluminum-based film is formed, or the other surface (the surface on which an aluminum-based film is not formed). EXAMPLES

[0055] EXAMPLES Next, the present invention will be described in more detail with reference to Examples, Comparative Examples and Reference Examples, but the present invention is not limited to the following Examples.

[0056] (1) Comparison with and without cavity Example 1 An optical filter was obtained according to the manufacturing method shown in Fig. 6. Specifically, a quartz substrate (thickness 0.5 mm) was used as the transparent substrate 11, and a solution obtained by diluting a random copolymer ("P6589-SMMAAEtMAran" manufactured by Polymer Source) with propylene glycol monomethyl ether acetate (PGMEA) to 1% was applied onto the transparent substrate 11, followed by heat treatment on a hot plate at 250°C for 2 minutes to form a neutral layer 51. Next, a solution 52 obtained by diblock copolymer ("P8380-SMMA" manufactured by Polymer Source) with 3% dilution with PGMEA was applied onto the neutral layer 51, followed by heat treatment on a hot plate at 250°C for 2 minutes and further treatment with acetic acid to form self-assembled dots 53 of polystyrene having a predetermined shape and arrangement pattern (circular in plan view, diameter 80 nm, maximum center-to-center distance 180 nm).

[0057] Next, O 2 The exposed neutral layer 51 was removed by plasma treatment, and then an aluminum film was formed as the aluminum-based film 21 on the exposed surface by sputtering to a thickness T1 of 90 nm. Then, the self-assembled dots 53 were removed using acetone, and a plurality of holes 22 were formed in the aluminum film. The holes 22 were arranged in a roughly regular pattern. Next, CF 4 The surface of the transparent substrate 11 directly below the holes 22 was processed by plasma etching using a gas to form cavities 12 with a depth of 50 nm. In this manner, the optical filter 100 was produced.

[0058] The obtained optical filter (Example 1) had an aluminum film thickness T1 = 90 nm, multiple holes 22 that were circular in plan view formed in the aluminum film, the hole diameter φ1 = 80 nm, the distance between the centers of adjacent holes (hole pitch) P1 was a maximum of 180 nm, and the cavity depth D1 = 50 nm.

[0059] Comparative Example 1 An optical filter was obtained in the same manner as in Example 1, except that plasma etching was not performed in Example 1. In the obtained optical filter (Comparative Example 1), no cavity was formed in the transparent substrate directly below the hole in the aluminum film.

[0060] Fig. 8 shows the transmission spectra in the wavelength range of 200 nm to 400 nm for the optical filters of Example 1 and Comparative Example 1. As can be seen from Fig. 8, in Example 1, the main peak near a wavelength of 220 nm is higher and the sub-peak near a wavelength of 300 nm is smaller, compared to Comparative Example 1. That is, it can be seen that the optical filter of Example 1 has improved separation performance from light with a wavelength of approximately 300 nm or more when transmitting light with a wavelength of 280 nm or less, compared to the optical filter of Comparative Example 1.

[0061] (2) Comparison by hole pitch (Reference examples 1~3) In Comparative Example 1, an optical filter was obtained in the same manner as in Comparative Example 1, except that the conditions for self-organization of the block copolymer were appropriately changed so that the thickness T1 of the aluminum film was 50 nm and the hole pitch P1 in the aluminum film was a maximum of 240 nm (Reference Example 1), a maximum of 200 nm (Reference Example 2), or a maximum of 180 nm (Reference Example 3).

[0062] FIG. 9 shows the transmission spectra in the wavelength range of 200 nm to 400 nm for the optical filters of Reference Examples 1 to 3. From FIG. 9, when the hole pitch P1 is a maximum of 240 nm, the main peak is near 300 nm, and when the hole pitch P1 is a maximum of 200 nm or 180 nm, the main peak is at a position of 300 nm or less. Therefore, it is essential to set the hole pitch to 200 nm or less for sensor applications for light with a wavelength of 280 nm or less. Note that Reference Examples 1 to 3 are examples in which no cavity is formed in the substrate, but in principle, it is considered that the same tendency as above can be seen even when a cavity is formed in the substrate.

[0063] (3) Comparison by cavity depth (Examples 2 to 5) An optical filter was obtained in the same manner as in Example 1, except that the plasma etching conditions were appropriately changed so that the cavity depth D1 was 10 nm (Example 2), 25 nm (Example 3), 75 nm (Example 4), or 100 nm (Example 5).

[0064] FIG. 10 shows the transmission spectra in the wavelength range of 200 nm to 400 nm for the optical filters of Examples 2 to 5, along with those of Example 1 and Comparative Example 1. FIG. 11 shows the transmittance in each example at a wavelength of 222 nm, which was the main peak in Example 1, and at a wavelength of 300 nm, which was the sub-peak in Example 1. It can be seen from FIGS. 10 and 11 that by forming a cavity, the transmittance at a wavelength of 222 nm (near the main peak) increases, while the transmittance at a wavelength of 300 nm (near the sub-peak) decreases. It can also be considered that the above effect can be obtained if the depth D1 of the cavity is 5 nm or more.

[0065] (4) Evaluation of optical filters using sapphire substrates (Example 6 and Comparative Example 2) Optical filters (Example 6, Comparative Example 2) were obtained in the same manner as Example 1, except that a sapphire substrate was used instead of the quartz substrate in Example 1 and Comparative Example 1. FIG. 12 shows the transmission spectra in the wavelength range of 200 nm to 400 nm for the optical filters of Example 6 and Comparative Example 2. FIG. 12 shows that, in Example 6, compared to Comparative Example 2, the height of the main peak located at wavelengths of 280 nm or less is maintained at the same level, while the sub-peak located at wavelengths of 300 nm or more is smaller. That is, it can be seen that the optical filter using the sapphire substrate also has improved separation performance from light with wavelengths of about 300 nm or more when transmitting light with wavelengths of 280 nm or less.

[0066] (5) Evaluation of optical filters with holes of different diameters Example 7 An optical filter (Example 7) was obtained in the same manner as in Example 1, except that the conditions for self-organization of the block copolymer were appropriately changed so that the hole pitch P1 in the aluminum film was set to a maximum of 200 nm and holes with diameters φ1 of 30 nm, 40 nm, 50 nm, and 60 nm were mixed (so as to have the approximate shape shown in FIG. 3). That is, T1 and D1 of the obtained optical filter (Example 7) were the same as those of Example 1.

[0067] Comparative Example 3 An optical filter was obtained in the same manner as in Example 7, except that plasma etching was not performed in Example 7. In the obtained optical filter (Comparative Example 3), no cavity was formed in the transparent substrate directly below the hole in the aluminum film.

[0068] The transmission spectra in the wavelength range of 200 nm to 400 nm for the optical filters of Example 7 and Comparative Example 3 are shown in Fig. 13. As can be seen from Fig. 13, in Example 7, the height of the main peak located at wavelengths of 280 nm or less is maintained at the same level, while the sub-peak located at wavelengths of 300 nm or more is smaller, compared to Comparative Example 3. That is, it can be seen that the optical filter containing a mixture of holes of different sizes also has improved separation performance from light with wavelengths of approximately 300 nm or more when transmitting light with wavelengths of 280 nm or less.

[0069] (6) Evaluation of optical filters with different hole diameters on the upper and lower surfaces of an aluminum-based film Example 8 An optical filter (Example 8) was obtained in the same manner as in Example 1, except that the conditions for self-organization of the block copolymer were appropriately changed so that the hole diameter φ11 on the outermost surface side of the hole formed in the aluminum film was 80 nm and the hole diameter φ12 on the transparent substrate side was 60 nm (so as to have an approximate shape as shown in FIG. 4). That is, T1, P1, and D1 of the obtained optical filter (Example 8) were the same as those in Example 1.

[0070] Comparative Example 4 An optical filter was obtained in the same manner as in Example 8, except that plasma etching was not performed in Example 8. In the obtained optical filter (Comparative Example 4), no cavity was formed in the transparent substrate directly below the hole in the aluminum film.

[0071] Fig. 14 shows the transmission spectra in the range of 200 nm to 400 nm for the optical filters of Example 8 and Comparative Example 4. As can be seen from Fig. 14, in Example 8, the main peak located at wavelengths of 280 nm or less is higher and the sub-peak located at wavelengths of 300 nm or more is smaller than in Comparative Example 4. That is, it can be seen that the optical filter in which the hole diameters are different between the upper and lower surfaces of the aluminum film also has improved separation performance from light with wavelengths of approximately 300 nm or more when transmitting light with wavelengths of 280 nm or less.

[0072] (7) Comparison by hole size (Reference examples 4 and 5) An optical filter was obtained in the same manner as in Comparative Example 1, except that the conditions for self-organization of the block copolymer were appropriately changed so that the hole diameter φ1 was 80 nm (Reference Example 4) or 120 nm (Reference Example 5) (Reference Example 4 was under the same conditions as Comparative Example 1).

[0073] FIG. 15 shows the transmission spectra in the wavelength range of 200 nm to 400 nm for the optical filters of Reference Examples 4 and 5. It can be seen from FIG. 15 that as the hole diameter φ1 becomes smaller, the main peak decreases, but the half-width also tends to become smaller. It can also be seen that as the hole diameter φ1 becomes smaller, the sub-peak tends to decrease. Note that Reference Examples 4 and 5 are examples in which no cavity is formed in the substrate, but in principle, it is believed that the same tendency as above will be observed even when a cavity is formed in the substrate.

[0074] Furthermore, from the evaluations of (6) and (7) above, it is expected that the desired transmittance and peak sharpness can be flexibly achieved by appropriately adjusting the hole diameter φ1, or the hole diameter φ11 on the upper surface side and the hole diameter φ12 on the lower surface side.

[0075] (8) Evaluation of optical filters with metal films other than aluminum-based films Comparative Example 5 In Example 1, instead of the aluminum film, gallium oxide (GaO 3 An optical filter was obtained in the same manner as in Example 1, except that a gallium oxide film was laminated on the quartz substrate as a transparent substrate. The obtained optical filter (Comparative Example 5) had a gallium oxide film with a thickness T1=90 nm laminated on the quartz substrate as a transparent substrate, and a plurality of holes were formed in the gallium oxide film that were circular in plan view, with the diameter φ1 of the holes being 80 nm and the distance between the centers of adjacent holes (hole pitch) P1 being 180 nm. In the obtained optical filter (Comparative Example 5), a plurality of cavities were formed in the transparent substrate directly below the holes in the gallium oxide film, and the depth D1 of the cavities was 50 nm.

[0076] Comparative Example 6 An optical filter was obtained in the same manner as in Example 1, except that a gallium nitride (GaN) film was laminated instead of the aluminum film in Example 1. The obtained optical filter (Comparative Example 6) had a gallium nitride film with a thickness T1=90 nm laminated on a quartz substrate as a transparent substrate, and a plurality of holes having a circular shape in a planar view were formed in the gallium nitride film, the diameter φ1 of the holes was 80 nm, and the distance between the centers of adjacent holes (hole pitch) P1 was 180 nm. In the obtained optical filter (Comparative Example 6), a plurality of cavities were formed in the transparent substrate directly below the holes in the gallium nitride film, and the depth D1 of the cavities was 50 nm.

[0077] The transmission spectra in the wavelength range of 200 nm to 400 nm for the optical filters of Comparative Examples 5 and 6 are shown in Fig. 16. It can be seen from Fig. 16 that when a film other than an aluminum-based film is disposed on a transparent substrate, even if holes and cavities are formed in a predetermined manner, the selectivity for transmission of light with a wavelength of 280 nm or less is poor, and the filter is not suitable for the applications envisaged in the present invention. [Industrial Applicability]

[0078] According to the present invention, it is possible to provide an optical filter that selectively transmits light with a wavelength of 280 nm or less while improving the performance of separating light with a wavelength of approximately 300 nm or more, and that can be easily manufactured. Furthermore, according to the present invention, it is possible to provide a photodiode module including the above-mentioned optical filter. Furthermore, according to the present invention, it is possible to provide a method for producing an optical filter, which can easily produce the above-mentioned optical filter. [Explanation of symbols]

[0079] 100 optical filter; 11 transparent substrate; 12 cavity; 21 aluminum-based film; 22 hole; 31 first laminated film; 41 second laminated film 51 Neutral layer; 52 Diblock copolymer solution; 53 Self-assembled dots; 200 photodiode; 251 substrate; 252 semiconductor layer; 253 electrode 300 Photodiode Module

Claims

1. A transparent substrate and an aluminum-based film disposed on the transparent substrate, the aluminum-based film has a plurality of holes, the distance between the centers of adjacent holes being 200 nm or less; An optical filter, characterized in that the transparent substrate has a plurality of cavities directly below the holes in the aluminum-based film, and the depth of the cavities based on the surface of the transparent substrate is 5 nm or more.

2. 2. The optical filter according to claim 1, wherein the holes in the aluminum-based film are circular in plan view, and a hole diameter on one film surface is different from a hole diameter on the other film surface.

3. 3. The optical filter according to claim 1, wherein the aluminum-based film contains silicon (Si) or copper (Cu) in a proportion of 10 mass % or less.

4. 4. The optical filter according to claim 1, wherein the transparent substrate is made of quartz or sapphire.

5. A photodiode module comprising: a photodiode having a semiconductor layer on a substrate; and the optical filter according to any one of claims 1 to 4.

6. The photodiode module according to claim 5 , wherein the optical filter is disposed in contact with a surface of the base material on which the semiconductor layer is not formed.

7. A method for producing the optical filter according to any one of claims 1 to 4, comprising the steps of: a film forming step of forming an aluminum-based film having a plurality of holes on a transparent substrate; Thereafter, a substrate processing step of forming a plurality of cavities on the transparent substrate through the plurality of holes, In the film formation step, holes are patterned by self-organization of a block copolymer or by two-beam interference exposure; In the substrate processing step, plasma etching is performed. A method for producing an optical filter.

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