JP7657698B2 - Optical filter, photodiode module, and method for manufacturing optical filter - Google Patents

Description

The present invention relates to an optical filter, a photodiode module, and a method for manufacturing an optical filter.

Demand for semiconductor light receiving elements for light with wavelengths of 280 nm or less (also known as deep ultraviolet light or UV-C) has been increasing in recent years. These elements are used as flame sensors for fire detection (Reference: flames generally include UV-C light) and sterilization monitors (Reference: UV-C is considered to have a sterilizing effect). There is particularly high demand for flame sensors as small sensors for security purposes.

The important practical performance of the semiconductor light receiving element described above is its ability to separate from the solar spectrum, which includes 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, active research on semiconductor structures is being conducted (Non-Patent Document 1).

There is also 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 have been proposed that use a dielectric multilayer film as such a filter (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.

Patent Document 3 discloses a filter in which openings are periodically provided in a thin metal film. This is a transmission filter in which openings smaller than the wavelength are provided in a thin conductive material film, and light propagating due to the 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. 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.

On the other hand, Patent Document 4 describes a layered structure of an aperture as a technique for removing the above-mentioned sub-peaks and transmitting only the desired wavelength range. Also, Non-Patent Document 3 realizes a narrow-band filter by increasing the number of layers in a metal mesh filter and providing a hollow section. However, although these conventional techniques use structural innovations to adjust and remove sub-peaks, such structures are complicated.

Yo Yoshikawa et al., "Development of Highly Sensitive Deep UV Sensors - From Photomultiplier Tubes to Solid-State Devices", OPTRONICS, 2020 Jinlian Hu et al., Dual-channel extraordinary ultraviolet transmission through an aluminum nanohole array: Nanotechnology 28 215205 (2017) 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

JP 2006-080782 A JP 2008-021460 A Japanese Patent Application Publication No. 11-072607 JP 2015-031856 A

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 about 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.

The inventors, keeping in mind that the degree of narrowbanding 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 discovered that by forming a cavity of a predetermined shape by surface processing on the transparent substrate on which the aluminum film is disposed, it is possible to reduce the sub-peak at wavelengths of approximately 300 nm or more and/or increase the main peak at wavelengths of 280 nm or less, which led to the invention.

The means to achieve the above objectives are as follows:

<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> The optical filter described in <1>, in which 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.

<3> The optical filter described in <1> or <2>, in which the aluminum-based film contains silicon (Si) or copper (Cu) in a proportion of 10 mass% or less.

<4> An optical filter according to any one of <1> to <3>, in which the transparent substrate is made of quartz or sapphire.

<5> A photodiode module comprising a photodiode having a semiconductor layer on a substrate and an optical filter described in any one of <1> to <4>.

<6> The photodiode module described in <5>, in which the optical filter is arranged in contact with a surface of the substrate on which the semiconductor layer is not formed.

<7> A method for producing the optical filter according to any one of <1> to <4>,
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.

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.

1 is a schematic plan view of an optical filter according to an embodiment of the present invention; 2 is a schematic cross-sectional view of the optical filter of FIG. 1 taken along line AA. FIG. 2 is a schematic plan view of an optical filter according to another embodiment of the present invention. FIG. 11 is a schematic cross-sectional view of an optical filter according to yet another embodiment of the present invention. FIG. 11 is a schematic cross-sectional view of an optical filter according to yet another embodiment of the present invention. FIG. 2 is a process flow diagram for explaining a method for manufacturing an optical filter according to an embodiment of the present invention. 1 is a schematic side view of a photodiode module according to an embodiment of the present invention; FIG. 11 is a diagram showing a comparison of transmission spectra with and without a cavity in this embodiment. FIG. 11 is a diagram showing a comparison of transmission spectra according to hole pitch in the present embodiment. FIG. 11 is a diagram showing a comparison of transmission spectra according to cavity depth in the present embodiment. FIG. 11 is a diagram showing a comparison of transmittance at a specific wavelength depending on the cavity depth in this embodiment. FIG. 11 is a diagram showing a comparison of transmission spectra with and without a cavity in this embodiment. FIG. 11 is a diagram showing a comparison of transmission spectra with and without a cavity in this embodiment. FIG. 11 is a diagram showing a comparison of transmission spectra with and without a cavity in this embodiment. FIG. 11 is a diagram showing a comparison of transmission spectra depending on the hole size in this embodiment. 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.

The present invention will be described in detail below based on the embodiments. Please note that the figures used in the description are presented to improve understanding of the invention, and that the scale, dimensional relationships, shapes, and other detailed structures of the components in each figure may be different from the actual ones.

(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 the "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.

Figure 1 shows a schematic plan view of the optical filter of this embodiment, and Figure 2 shows a schematic cross-sectional view of the optical filter of Figure 1 taken along line A-A. As shown in Figure 2 in particular, the optical filter 100 has a structure that includes 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, as shown in Figure 2, it is preferable that the transparent substrate 11 and the aluminum-based film 21 of the optical filter 100 are in direct contact with each other.

The optical filter 100 also has a plurality of holes 22 (portions penetrating the entire 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 be observed in the light transmission spectrum with a main peak on the low wavelength side and a sub-peak on the high wavelength side. Note that, for ease of explanation, only four holes 22 are shown in FIG. 1 and other figures, but typically an infinite number of holes 22 are formed on the aluminum-based film 21.

The planar shape of the holes 22 is not particularly limited. For example, as shown in FIG. 1, they may be circular (including perfect circles and ellipses), or they may be polygonal (including triangular and rectangular), 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 (diameters, etc.).

The multiple holes 22 formed in the aluminum-based film 21 may be arranged in a regular pattern or may be arranged randomly.

Furthermore, as shown in FIG. 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. Therefore, the optical filter 100 as a whole can be recognized as forming one cavity by 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 a cavity 12 in the substrate (transparent substrate 11) itself, as in the optical filter 100 of this embodiment, is at least considered to be novel.

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.

In addition, in FIG. 1, the pitch between two diagonal holes of the four holes that are arranged so that their center points are connected to form a rectangle is shown as P1, but this is merely the pitch with the longest distance shown as P1 in FIG. 1. In other words, the optical filter of this embodiment requires that the distance between the centers of any two arbitrarily selected adjacent holes is 200 nm or less.

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 the height of the sub-peak can be reduced. 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). In addition, 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, from the viewpoint of more sufficiently improving the separation performance with light having a wavelength of about 300 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.

In the optical filter 100 of this embodiment, as shown in FIG. 2, it is preferable that there is no step between the hole 22 and the cavity 12, and that they are smoothly connected. In other words, in the optical filter 100 of this embodiment, it is preferable that the planar shape of the hole 22 and the planar shape of the cavity 12 are substantially the same.

The material of the transparent substrate 11 is not particularly limited as long as it has transparency, and examples thereof include inorganic materials and plastic materials. Examples of inorganic materials include silica such as quartz, sapphire, diamond, and the like. Among these, inorganic materials are preferred as the material of the transparent substrate from the viewpoints of marketability, processability, stability, and the like, and quartz or sapphire are more preferred, with quartz being even more preferred.

The thickness of the transparent substrate 11 is not particularly limited, but from the viewpoint of ease of handling during manufacturing and mechanical stability, it is preferable that the thickness be 0.1 mm or more and 10 mm or less.

The aluminum-based film 21 is a film that contains at least aluminum or an aluminum compound. The aluminum-based film 21 may also be an alloy. However, from the viewpoint of obtaining the desired transmission characteristics, the proportion 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.

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 particle size of the aluminum can be reduced, making it easier to produce the aluminum-based film 21 having the desired shape (the configuration of the multiple holes 22).

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 preferable that it be 50 nm or more, and from the viewpoint of productivity, it is preferable that it be 100 nm or less.

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.
In addition, when the shape of the hole 22 in plan view is a shape other than a circle, the "hole size W1" is the longest length of the line segments connecting two points on the contour line of the hole. In addition, in this specification, when the shape of the hole in plan view is a circle, the hole size W1 may be referred to as the hole diameter φ1.

Figure 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, as shown in Figure 3, the size W1 of the multiple holes 22 in the aluminum-based film may be different.

Figure 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 Figure 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 fabricate 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.

Figure 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, as shown in Figure 5, one or more metal films may be further disposed on the aluminum-based film 21. In this case, a plurality of holes 22 are formed in the metal film at the same locations as the aluminum-based film 21.

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, and 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 thicknesses of these laminated films can be appropriately adjusted depending on the purpose.

(Method of Manufacturing Optical Filter)
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 through 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 the manufacturing method of this embodiment, the above-mentioned optical filter can be easily manufactured.

Figure 6 is a process flow diagram illustrating an example of the manufacturing method of this embodiment. In this manufacturing method, the block copolymer is self-assembled in the film formation process.

<Film formation process>
First, a transparent substrate 11 is prepared (FIG. 6(a)), and a neutral layer 51 is formed on the transparent substrate 11 (FIG. 6(b)). The neutral layer 51 can be formed as a random copolymer layer, for example, by applying a solution of a random copolymer dissolved in a solvent and heating it. The 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.

Next, a solution (diblock copolymer solution 52) made 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 self-assembled into polymer components on the substrate, resulting in an arrangement of two polymers with periodicity. Furthermore, by utilizing the difference in etching resistance between the polymer components, the other polymer is removed by plasma etching or chemicals to form uneven self-assembled dots 53 with 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.

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.

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

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 removal methods include surface treatment with a solvent and a lift-off process using a solvent in combination.

<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 examples of gases used in the plasma etching include carbon tetrafluoride (CF ₄ ) and sulfur hexafluoride (SF ₆ ). Also, by appropriately changing the plasma etching conditions, the cavity depth D1 in the transparent substrate 11 can be adjusted.

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

(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.

The arrangement of each component 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 at a distance from the substrate and the semiconductor layer (photodiode).

Figure 7 is a schematic side view of a photodiode module according to one embodiment of the present invention. The photodiode module 300 in Figure 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 Figure 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 formed directly on the substrate 251, the arrangement shown in Figure 7 has the advantage that it can be applied 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.

The surface of the optical filter 100 that faces the substrate 251 in the photodiode module is not particularly limited, and may be the surface on which the aluminum-based film is formed, or the other surface (the surface on which the aluminum-based film is not formed).

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.

(1) Comparison with and without a 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 (Polymer Source's "P6589-SMMAAAEtMAran") with propylene glycol monomethyl ether acetate (PGMEA) to 1% was applied onto the transparent substrate 11, and the solution was heated on a hot plate at 250°C for 2 minutes to form a neutral layer 51. Next, a solution 52 obtained by diblock copolymer (Polymer Source's "P8380-SMMA") with 3% PGMEA was applied onto the neutral layer 51, and then the solution was heated on a hot plate at 250°C for 2 minutes and further treated 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).

Next, the exposed neutral layer 51 was removed by _O2 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 = 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, the surface of the transparent substrate 11 directly below the plurality of holes 22 was processed by plasma etching using _CF4 gas, and a cavity 12 with a depth of 50 nm was formed. In this manner, the optical filter 100 was produced.

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.

(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.

Figure 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 Figure 8, in Example 1, the main peak near a wavelength of 220 nm is higher than in Comparative Example 1, and the sub-peak near a wavelength of 300 nm is smaller. In other words, 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.

(2) Comparison by hole pitch (Reference Examples 1 to 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).

Figure 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 Figure 9, when the hole pitch P1 is a maximum of 240 nm, the main peak is near 300 nm, and when it is a maximum of 200 nm or 180 nm, the main peak is at a position below 300 nm. Therefore, it is essential that the hole pitch be 200 nm or less for sensor applications for light with wavelengths 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 believed that the same tendency as above will be observed even when a cavity is formed in the substrate.

(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).

For the optical filters of Examples 2 to 5, the transmission spectra in the wavelength range of 200 nm to 400 nm are shown in FIG. 10 along with Example 1 and Comparative Example 1. Also, the transmittance in each example at the wavelength of 222 nm, which was the main peak in Example 1, and at the wavelength of 300 nm, which was the sub-peak in Example 1, is shown in FIG. 11. It can be seen from FIG. 10 and FIG. 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.

(4) Evaluation of Optical Filter Using Sapphire Substrate (Example 6 and Comparative Example 2)
Optical filters (Example 6, Comparative Example 2) were obtained in the same manner as in 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. As shown in FIG. 12, in Example 6, the height of the main peak located at a wavelength of 280 nm or less is maintained at the same level as in Comparative Example 2, while the sub-peak located at a wavelength 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 a wavelength of about 300 nm or more when transmitting light with a wavelength of 280 nm or less.

(5) Evaluation of an optical filter containing 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.

(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.

Figure 13 shows the transmission spectra in the wavelength range of 200 nm to 400 nm for the optical filters of Example 7 and Comparative Example 3. As can be seen from Figure 13, in Example 7, compared to Comparative Example 3, 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. In other words, it can be seen that an 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.

(6) Evaluation of an optical filter having 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.

(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.

Figure 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 Figure 14, in Example 8, the main peak located at wavelengths of 280 nm or less is higher than in Comparative Example 4, and the sub-peak located at wavelengths of 300 nm or more is smaller. In other words, it can be seen that an optical filter in which the hole diameters are different on 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.

(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).

Figure 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. From Figure 15, it can be seen 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 if a cavity is formed in the substrate.

The above evaluations (6) and (7) suggest 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.

(8) Evaluation of optical filters having metal films other than aluminum-based films (Comparative Example 5)
An optical filter was obtained in the same manner as in Example 1, except that a gallium oxide (GaO ₃ ) film was laminated instead of the aluminum film in Example 1. The obtained optical filter (Comparative Example 5) has a gallium oxide 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 plan view are formed in the gallium oxide film, the diameter φ1 of the holes is 80 nm, and the distance between the centers of adjacent holes (hole pitch) P1 is 180 nm. In addition, in the obtained optical filter (Comparative Example 5), a plurality of cavities are formed in the transparent substrate directly below the holes in the gallium oxide film, and the depth D1 of the cavities is 50 nm.

(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) has 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 plan view are formed in the gallium nitride film, the diameter φ1 of the holes is 80 nm, and the distance between the centers of adjacent holes (hole pitch) P1 is 180 nm. In addition, in the obtained optical filter (Comparative Example 6), a plurality of cavities are formed in the transparent substrate directly below the holes in the gallium nitride film, and the depth D1 of the cavities is 50 nm.

Figure 16 shows the transmission spectra in the wavelength range of 200 nm to 400 nm for the optical filters of Comparative Examples 5 and 6. From Figure 16, it can be seen 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 specified manner, the selectivity for the transmission of light with wavelengths of 280 nm or less is poor, and this is not suitable for the optical filters intended for use in the present invention.

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.

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 Base material; 252 Semiconductor layer; 253 Electrode 300 Photodiode module

Claims (7)

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. The optical filter of claim 1, wherein 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. The optical filter according to claim 1 or 2, wherein the aluminum-based film contains silicon (Si) or copper (Cu) in a proportion of 10 mass% or less. The optical filter according to any one of claims 1 to 3, wherein the transparent substrate is made of quartz or sapphire. A photodiode module comprising a photodiode having a semiconductor layer on a substrate and an optical filter according to any one of claims 1 to 4. The photodiode module according to claim 5, wherein the optical filter is disposed in contact with a surface of the substrate on which the semiconductor layer is not formed. 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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