Optical filter, near-infrared light sensor module, and method for manufacturing optical filter

Abstract

Provided is an optical filter comprising a base material and a dielectric multilayer film provided on at least one main surface of the base material, wherein: the dielectric multilayer film is a laminate in which one or more of each of a low-refractive-index film, a medium-refractive-index film, and a high-refractive-index film are laminated; the dielectric multilayer film has at least one structure in which a low-refractive-index film, a medium-refractive-index film, a barrier film, and a high-refractive-index film are laminated in the stated order; the medium-refractive-index film includes one or more of an oxide, a nitride, an oxynitride, and a fluoride of a first element; the barrier film includes one or more of an oxide, a nitride, an oxynitride, and a fluoride of a second element; the thickness of the barrier film is 80 nm or less; in a wavelength region of 800-1600 nm, the average extinction coefficient of the second element is smaller than the average extinction coefficient of the first element; and the high-refractive-index film includes one or more of silicon, germanium, and silicon germanium.

Description

Optical filter, near-infrared light sensor module, and method for manufacturing an optical filter

[0001] This disclosure relates to an optical filter, a near-infrared light sensor module, and a method for manufacturing an optical filter.

[0002] As an optical filter having optical properties that selectively transmit near-infrared light, a configuration is known in which a dielectric multilayer film is laminated on the main surface of a substrate. For example, Patent Document 1 discloses a configuration in which the dielectric multilayer film is laminated in the order of a low refractive index film, a medium refractive index film, and a high refractive index film in such an optical filter as described above.

[0003] Japanese Patent Publication No. 2023-55684

[0004] Patent Document 1 describes that the disclosed laminated structure can suppress the increase in near-infrared light reflectivity even for light at high incident angles while maintaining high transmittance of near-infrared light. However, in recent years, there has been a demand for further improvement in the optical properties of optical filters, and in particular, a demand for further increase in the transmittance of near-infrared light.

[0005] In view of the above, one aspect of the present disclosure provides an optical filter that can obtain a high transmittance of near-infrared light while suppressing the increase in reflectance of near-infrared light for light at high incident angles.

[0006] One aspect of the present disclosure is an optical filter comprising a substrate and a dielectric multilayer film provided on at least one main surface of the substrate, wherein the dielectric multilayer film is a laminate in which one or more layers of a low refractive index film, a medium refractive index film, and a high refractive index film are laminated, the dielectric multilayer film has at least one structure in which the low refractive index film, medium refractive index film, barrier film, and high refractive index film are laminated in that order, the barrier film contains one or more oxides, nitrides, oxynitrides, and fluorides of a second element, the thickness of the barrier film is 80 nm or less, the mean extinction coefficient of the second element is smaller than the mean extinction coefficient of the first element in the wavelength range of 800 to 1600 nm, and the high refractive index film is a silicon film, a germanium film, or a silicon germanium film.

[0007] Another aspect of the present disclosure is an optical filter comprising a substrate and a dielectric multilayer film provided on at least one main surface of the substrate, wherein the dielectric multilayer film is a laminate in which one or more layers of a low refractive index film, a medium refractive index film, and a high refractive index film are laminated, the dielectric multilayer film has at least one structure in which the low refractive index film, medium refractive index film, barrier film, and high refractive index film are laminated in that order, the medium refractive index film comprises one or more oxides, nitrides, oxynitrides, and fluorides of a first element, the barrier film comprises one or more oxides, nitrides, oxynitrides, and fluorides of a second element, the thickness of the barrier film is 80 nm or less, the second element comprises one or more silicon and germanium, and the high refractive index film is a silicon film, a germanium film, or a silicon germanium film.

[0008] According to one aspect of this disclosure, an optical filter can be provided that can obtain a high transmittance of near-infrared light while suppressing the increase in reflectance of near-infrared light for light at high incident angles.

[0009] This figure schematically shows the structure of an optical filter according to one embodiment of the present disclosure. It is an enlarged view of part Q in Figure 1, and schematically shows the substructure.

[0010] The embodiments of this disclosure will be described below with reference to the drawings. In each drawing, the same or corresponding components will be denoted by the same reference numeral, and their descriptions may be omitted. The drawings are schematic in order to help understand the configuration of this disclosure, and some dimensions may be shown larger or smaller than they actually are. In the specification, the "~" indicating a numerical range means that the numbers before and after it are included as the lower and upper limits, respectively.

[0011] <Optical Filter> An optical filter according to one embodiment of the present disclosure may be an optical filter comprising a substrate and a dielectric multilayer film provided on at least one main surface of the substrate. Figure 1 shows a schematic diagram of an optical filter 1 according to one embodiment of the present disclosure. In the optical filter 1 shown in Figure 1, dielectric multilayer films S1 and S2 (collectively referred to as dielectric multilayer film S) are provided on both main surfaces of the substrate 10, respectively. However, the dielectric multilayer film S does not necessarily have to be formed on both main surfaces of the substrate 10, and the optical filter 1 may be in a form in which the dielectric multilayer film S1 or S2 is provided on one main surface of the substrate 10. The configuration of the dielectric multilayer films S1 and S2 (materials constituting the films, film thickness, number of films, etc.) may be the same or different.

[0012] In the optical filter 1, the dielectric multilayer film S may be laminated in contact with the substrate 10, but another layer may be additionally provided between the dielectric multilayer film S and the substrate 10.

[0013] Furthermore, the optical filter 1 may have components other than the substrate 10 and the dielectric multilayer film S, as needed. For example, the dielectric multilayer film S may have an anti-fouling film on its surface to make it easier to remove dirt from the surface of the optical filter 1, an anti-glare film to scatter ambient light and improve visibility, or a water-repellent film to make it easier to remove water from the surface of the optical filter 1. In addition, the optical filter 1 may have a conductive film on its surface or on the side facing the substrate 10 in order to provide it with a heater function or an electromagnetic interference (EMI) countermeasure function.

[0014] The optical filter 1 according to this embodiment has the characteristic of selectively transmitting near-infrared light, more specifically, the characteristic of blocking visible light and transmitting near-infrared light (hereinafter also referred to as near-infrared light selective light transmission). The optical filter 1 can be used, for example, as a cover in a sensor module that detects reflected light after irradiating an object with near-infrared light, such as near-infrared laser light. Such a sensor module is suitably used in LiDAR sensors, particularly automotive LiDAR sensors.

[0015] <Substrate> The material used for the substrate 10 in the optical filter 1 according to this embodiment is not particularly limited as long as it is a material that can transmit near-infrared light, and may be an inorganic material or an organic material. Examples of inorganic materials include silicon and glass. The substrate 10 may also be a birefringent crystalline material such as quartz, lithium niobate, or sapphire.

[0016] Examples of glass include soda-lime glass, borosilicate glass, alkali-free glass, quartz glass, and aluminosilicate glass. Furthermore, chemically strengthened glass may also be used.

[0017] The base material may have a single-layer structure, or it may have a multi-layer structure, for example, a structure in which two or more base materials are joined together.

[0018] The shape of the substrate 10 is not particularly limited and may be block-shaped, plate-shaped, film-shaped, etc. Furthermore, the thickness of the substrate may be preferably 0.1 to 5 mm, more preferably 2 to 4 mm, from the viewpoint of reducing warping when forming the dielectric multilayer film, reducing the height of the optical filter, and suppressing cracking.

[0019] <Dielectric Multilayer Film> The dielectric multilayer film S provided on at least one main surface of the substrate 10 has near-infrared light selective light transmittance, that is, optical selectivity that blocks visible light and transmits near-infrared light.

[0020] The dielectric multilayer film S is a film made up of multiple dielectric films of different types stacked on top of each other. In this embodiment, the dielectric multilayer film S is made up of multiple dielectric films of different refractive indices stacked on top of each other, thereby having the infrared light selective transmittance described above.

[0021] Figure 2 schematically shows a part of the layered structure (substructure U) contained in the dielectric multilayer film S as an enlarged view of part Q in Figure 1. The dielectric multilayer film S is a film containing many films with different refractive indices, more specifically, a film containing one or more layers each of a low refractive index film, a medium refractive index film, and a high refractive index film. As shown in Figure 2, the dielectric multilayer film S includes at least one substructure U in which a low refractive index film L, a medium refractive index film M, a barrier film BR, and a high refractive index film H are layered in this order. In this substructure U, the layering order of the low refractive index film L, medium refractive index film M, barrier film BR, and high refractive index film H may be in the direction away from the substrate 10 or in the direction approaching the substrate 10. Furthermore, the substructure U may be layered in direct contact with the substrate 10, or another layer may be interposed between the substrate 10 and the substructure U.

[0022] In this specification, the terms "low refractive index," "medium refractive index," and "high refractive index" do not refer to specific numerical ranges of refractive index, but rather to the relative refractive index relationships between the films contained in the dielectric multilayer film S of the optical filter 1. Therefore, the low refractive index film L is a film with a lower refractive index than the medium refractive index film M, and the medium refractive index film M is a film with a lower refractive index than the high refractive index film H.

[0023] The low refractive index film L is a metallic compound, and more specifically, may contain one or more metal oxides, nitrides, oxynitrides, and fluorides. Examples of the metallic elements include Si and Al. An example of a material for the low refractive index film L is SiO ２ SiO ｘ N ｙ , SiO, SiN, Al ２ O ３ These include SiO2, which is inexpensive and easy to handle. ２ This is preferable. The refractive index of the low refractive index film L is preferably 2.0 or less, more preferably 1.5 or less. In this specification, unless otherwise specified, "refractive index" refers to the refractive index for light with a wavelength of 550 nm at 20°C.

[0024] The intermediate refractive index film M is also a metal compound. More specifically, it contains one or more of metal oxides, nitrides, oxynitrides, and fluorides. In this specification, the metal contained in the metal oxide constituting the intermediate refractive index film M is particularly referred to as the "first element". Examples of the first element include Ta, Nb, Ti, Zr, Hf, Si, Al, etc. Examples of the material of the intermediate refractive index film M include Ta ２ O ５ , Nb ２ O ５ , TiO, ZrO ２ , HfO ２ , SiO, Al ２ O ３ etc. Among these, from the viewpoints of having a large effect of suppressing the reflectance for near-infrared light at a high incident angle and having high reproducibility of optical constants, Nb ２ O ５ , Ta ２ O ５ are preferable, and Nb ２ O ５ is more preferable. The refractive index of the intermediate refractive index film M may preferably be 1.6 to 3.0, more preferably 1.8 to 2.5.

[0025] Examples of the material of the high refractive index film H include silicon (Si), germanium (Ge), and silicon germanium (SiGe). That is, the high refractive index film H may be a silicon film, a germanium film, or a silicon germanium film. Among the above materials, amorphous silicon is preferable from the viewpoint of having high visible light absorption ability, and hydrogen-free amorphous silicon (a-Si) is more preferable. The refractive index of the high refractive index film H may preferably be 3.0 or more, more preferably 4.0 or more.

[0026] The thickness of the low refractive index film L (the film thickness of one low refractive index film L) may preferably be 2 to 500 nm, more preferably 10 to 400 nm. The thickness of the medium refractive index film M (the film thickness of one medium refractive index film M) may preferably be 2 to 500 nm, more preferably 40 to 400 nm. The thickness of the high refractive index film H (the film thickness of one high refractive index film H) may preferably be 2 to 300 nm, more preferably 5 to 200 nm. Further, from the viewpoint of suppressing the absorption of near infrared rays by the high refractive index film H, the thickness of the high refractive index film H included in the partial structure U is preferably 150 nm or less, more preferably 100 nm or less.

[0027] As shown in FIG. 2, the partial structure U in the dielectric multilayer film S includes a low refractive index film L, a medium refractive index film M, and a high refractive index film H in this stacking order. By having a partial structure in which films with a stepwise changing refractive index are stacked, the transmittance of near infrared light can be made relatively high by the interference effect of light, and the reflectance of near infrared light can be kept low even for light with a large incident angle (even for light with a high incident angle). In this specification, the "incident angle" refers to the angle with respect to the normal direction of the main surface irradiated with light on the optical filter (the direction perpendicular to the main surface of the optical filter). The "large incident angle" or "high incident angle" refers to an angle where the direction of the incident light is, for example, 45° or more, 60° or more, or 75° or more with respect to the above normal direction and less than 90°, particularly referring to an incident angle of 60°. Also, in this specification, when simply referring to "transmittance" or "reflectance" without specifying the incident angle, it refers to the transmittance or reflectance at an incident angle of 0°.

[0028] Furthermore, in the present embodiment, as shown in FIG. 2, a barrier film BR is provided between the medium refractive index film M and the high refractive index film H. The inventors of the present invention have found that by interposing the barrier film BR between the medium refractive index film M and the high refractive index film H in this way, the transmittance of near-infrared light can be increased as compared with the case where there is no barrier film BR. This is because when the medium refractive index film M and the high refractive index film H are in direct contact, a chemical reaction may occur between the medium refractive index film M and the high refractive index film H, which may prevent the near-infrared light transmittance of the dielectric multilayer film. However, it is considered that such a possibility can be avoided by the interposition of the barrier film BR. More specifically, due to the transfer of electrons at the interface between the medium refractive index film M and the high refractive index film H, the metal compound near the interface of the medium refractive index film M is reduced and an extremely thin metal single layer appears. It is considered that this metal single layer affects the light interference effect due to the partial structure, but such an effect can be blocked or reduced by the barrier film BR.

[0029] Therefore, the barrier film BR is not particularly limited as long as it can prevent the metal compound constituting the medium refractive index film M from becoming a metal single body and, even if a part of the barrier film BR is reduced, does not affect or hardly affects the original light interference effect of the partial structure. However, the barrier film BR is preferably a metal compound, and more specifically, it may contain one or more of metal oxides, nitrides, oxynitrides, and fluorides. The metal contained in the metal oxide constituting the barrier film BR is particularly referred to as the "second element".

[0030] Furthermore, in the present embodiment, in the wavelength range of 800 to 1600 nm, the average attenuation coefficient of the metal (second element) contained in the metal compound constituting the barrier film BR is made smaller than the average attenuation coefficient of the metal (first element) contained in the metal compound constituting the above-mentioned medium refractive index film M. Even if a part of the metal compound of the barrier film BR undergoes a chemical reaction and is reduced, the influence on the light interference effect of the partial structure is absent or small, so that a high transmittance of near-infrared light is maintained.

[0031] Furthermore, in the wavelength range of 800 to 1600 nm, the average extinction coefficient of the metal (second element) contained in the metal compound constituting the barrier film BR may be 0.01 or less. From the viewpoint of improving the transmittance of near-infrared light, the average extinction coefficient of the second element is preferably 0.005 or less, and more preferably 0.0025 or less. The average extinction coefficient of the second element may be 0.0001 or more. In addition, the average extinction coefficient of the metal (first element) contained in the metal compound constituting the medium refractive index film M may be 0.01 or more and 10 or less.

[0032] Furthermore, the second element mentioned above, that is, the element of the metal contained in the metal compound constituting the barrier film BR, includes Si, Ge, and Al, and it is preferable that it is at least one of Si and Ge, and more preferably Si. Since the metal (second element) contained in the metal compound constituting the barrier film BR is at least one of Si and Ge, even if a part of the metal compound of the barrier film BR undergoes a chemical reaction and is reduced, as described above, there is no or only a small effect on the optical interference effect of the substructure, and a high transmittance of near-infrared light is maintained.

[0033] Specific examples of barrier film BR materials include SiO ２ SiO ｘ N ｙ , SiO, SiN, GeO ２ , GeO ｘ N ｙ , GeO, Al ２ O ３ These are some examples. Of these, SiO is preferred because it is inexpensive and easy to handle. ２ , GeO ２ , fuwaSiO ２ This may be the case. The refractive index of the barrier film BR is preferably 2.0 or less, more preferably 1.5 or less. Thus, the material constituting the barrier film BR may be the same as the material constituting the low refractive index film L.

[0034] The thickness of the barrier film BR (the thickness of one barrier film) is 80 nm or less, preferably 60 nm or less, more preferably 40 nm, even more preferably 30 nm or less, even more preferably 20 nm or less, and even more preferably 15 nm or less. By having a barrier film BR thickness of 80 nm or less, the possibility of the barrier film BR becoming excessively thick and hindering the original optical interference effect of the substructure U can be reduced, thereby increasing the transmittance of near-infrared light and reducing the reflectance of near-infrared light at large incident angles. Furthermore, when trying to obtain an optical filter 1 with low reflectance in the visible light region, a barrier film BR thickness of 40 nm or less makes it easier to obtain low reflectance in the visible region. By reducing the reflectance of light in the visible region, the light reflected by the dielectric multilayer film S and, consequently the optical filter 1, is less likely to enter the human eye, and the optical filter 1 appears black, thus improving the design of the optical filter 1.

[0035] The lower limit of the barrier film BR thickness is not particularly limited, but in light of manufacturing constraints, the barrier film BR thickness may be 2 nm or more. Preferably, the barrier film BR thickness does not exceed the thickness of the high refractive index film H, the medium refractive index film M, or the low refractive index film L included in the substructure U.

[0036] Furthermore, in the dielectric multilayer film S, it is preferable that the medium refractive index film M does not come into contact with the high refractive index film H. This avoids reactions between the medium refractive index film M and the high refractive index film H, thereby improving the effect of obtaining high transmittance of near-infrared light while suppressing the increase in reflectance of near-infrared light for light at high incident angles.

[0037] From the viewpoint of increasing the transmittance of near-infrared light and keeping the reflectance of near-infrared light low even at high incident angles, the total number of substructures U included in the dielectric multilayer films S1 and S2 (the sum of the number of substructures U in one optical filter) is preferably 2 or more, more preferably 3 or more, and even more preferably 4 or more. The total number of films in the dielectric multilayer film S (the sum of the number of films in one dielectric multilayer film S) is preferably 2 to 40 layers, more preferably 8 to 30 layers. In addition, the total number of films in the dielectric multilayer films S1 and S2 (the total number of films in one optical filter) is preferably 4 to 80 layers, more preferably 16 to 60 layers. The number of films in the dielectric multilayer film S1 or S2, or in the optical filter 1 as a whole, can be appropriately determined from the viewpoint of improving the selective transmittance of near-infrared light, suppressing the reflection of visible light, and / or preventing deterioration of productivity due to layer switching and preventing a decrease in film thickness controllability due to an increase in the number of films.

[0038] Furthermore, the total number of high-refractive-index films H in the dielectric multilayer film S (the sum of the number of films in one side of the dielectric multilayer film S) may preferably be 1 to 15 layers. The total number of medium-refractive-index films M in the dielectric multilayer film S may preferably be 2 to 8 layers. Furthermore, the total number of low-refractive-index films L may preferably be 3 to 15 layers. The total number of each film type in the dielectric multilayer film S can also be appropriately determined from the viewpoint of improving the selective transmittance of near-infrared light, suppressing the reflection of visible light, and / or preventing deterioration of productivity due to layer switching and preventing a decrease in film thickness controllability due to an increase in the number of films.

[0039] The thickness of one dielectric multilayer film S is preferably 0.3 to 4 μm, more preferably 1 to 2 μm. Furthermore, if dielectric multilayer films S1 and S2 are formed on both main surfaces of the substrate 10, the sum of the thicknesses of both dielectric multilayer films S1 and S2 (total film thickness) is preferably 0.6 to 5.5 μm, more preferably 2 to 4 μm.

[0040] For forming the dielectric multilayer film S, dry deposition processes such as CVD, sputtering, and vacuum deposition, and wet deposition processes such as spraying and dipping can be used.

[0041] <Optical Characteristics (Spectroscopic Characteristics) of the Optical Filter> The optical filter according to this embodiment may have the following optical characteristics (spectroscopic characteristics). Such optical characteristics can be measured using a spectrophotometer.

[0042] (1) The maximum transmittance (T800-1600(0) MAX) at an incident angle of 0° in the wavelength range of 800 to 1600 nm is preferably 90% or more, 93% or more, 95% or more, 98% or more, 98.2% or more, 98.5% or more, 98.8% or more, 99% or more, or 99.5% or more, and may be 100%. (2) The minimum reflectance (R800-1600(60) MIN) at an incident angle of 60° in the wavelength range of 800 to 1600 nm is preferably 2.0% or less, 1.5% or less, 1.3% or less, 1.0% or less, 0.9% or less, 0.8% or less, 0.5% or less, or 0.3% or less. (3) The average transmittance at an incident angle of 0° in the wavelength range of 400 to 680 nm (T400-680(0)AVE) is preferably 10% or less, 8% or less, 5% or less, 3% or less, 2% or less, or 1% or less, and may be 0%. (4) The average reflectance at an incident angle of 5° in the wavelength range of 400 to 680 nm (R400-680(5)AVE) depends on the material of the substrate 10, but may be 55% or less, 45% or less, 30% or less, or 25% or less. Furthermore, when a transparent material is used as the substrate 10, it is preferably 10% or less, 8% or less, 5% or less, or 3% or less.

[0043] The optical properties described in (1) to (4) above may be those measured for the entire optical filter 1 when dielectric multilayer films S1 and S2 are laminated on both main surfaces of the substrate 10, respectively.

[0044] The optical filter 1 having the characteristic described in (1) above provides high transmittance of near-infrared light. Furthermore, the optical filter 1 having the characteristic described in (2) above enables high transmittance of near-infrared light regardless of the angle of incidence. Therefore, when an optical filter having the characteristics described in (1) and (2) above is used, for example, in the cover of a sensor that detects near-infrared light, the function of the sensor can be improved. In addition, if the optical filter 1 has the characteristic described in (3) above in addition to the characteristic described in (1) above, its ability to transmit near-infrared light and block visible light is enhanced, improving the selective transmittance of near-infrared light and thus improving the function of sensors and the like.

[0045] Furthermore, the characteristic described in (4) above makes it difficult for visible light to be reflected, and the characteristics described in (3) and (4) above make it difficult for visible light to be transmitted and reflected, so the color of the optical filter 1 can be perceived as black, thereby improving the aesthetic appeal of the optical filter 1.

[0046] In this specification, "maximum transmittance" in a given wavelength range refers to the maximum value obtained when the transmittance is measured at 1 nm intervals within that wavelength range. "Minimum reflectance" in a given wavelength range refers to the minimum value obtained when the reflectance is measured at 1 nm intervals within that wavelength range. Furthermore, "average transmittance" in a given wavelength range refers to the arithmetic mean of the transmittances measured at 1 nm intervals within that wavelength range, and "average reflectance" refers to the arithmetic mean of the reflectances measured at 1 nm intervals within that wavelength range.

[0047] One embodiment of the present disclosure is a method for manufacturing an optical filter comprising a substrate and a dielectric multilayer film provided on at least one main surface of the substrate, wherein the dielectric multilayer film is a laminate in which one or more layers of a low refractive index film, a medium refractive index film, and a high refractive index film are laminated on the substrate, and the dielectric multilayer film is formed such that it has at least one structure comprising a low refractive index film, a medium refractive index film, a barrier film, and a high refractive index film in this order, the medium refractive index film comprises one or more oxides, nitrides, oxynitrides, and fluorides of a first element, the barrier film comprises one or more oxides, nitrides, oxynitrides, and fluorides of a second element, the thickness of the barrier film is 80 nm or less, the mean extinction coefficient of the second element is smaller than the mean extinction coefficient of the first element in the wavelength range of 800 to 1600 nm, and the high refractive index film is a silicon film, a germanium film, or a silicon germanium film.

[0048] Furthermore, another embodiment is an optical filter comprising a substrate and a dielectric multilayer film provided on at least one main surface of the substrate, wherein the dielectric multilayer film is a laminate on the substrate in which one or more layers each of a low refractive index film, a medium refractive index film, and a high refractive index film are laminated, and the dielectric multilayer film is formed such that it has at least one structure in which a low refractive index film, a medium refractive index film, a barrier film, and a high refractive index film are included in this order, wherein the medium refractive index film contains one or more oxides, nitrides, oxynitrides, and fluorides of a first element, the barrier film contains one or more oxides, nitrides, oxynitrides, and fluorides of a second element, the thickness of the barrier film is 80 nm or less, the mean extinction coefficient of the second element is smaller than the mean extinction coefficient of the first element in the wavelength range of 800 to 1600 nm, and the high refractive index film is a silicon film, a germanium film, or a silicon germanium film.

[0049] Another embodiment of the present disclosure is a method for manufacturing an optical filter comprising a substrate and a dielectric multilayer film provided on at least one main surface of the substrate, wherein the dielectric multilayer film is a laminate in which one or more layers of a low refractive index film, a medium refractive index film, and a high refractive index film are laminated on the substrate, and the dielectric multilayer film has at least one structure comprising a low refractive index film, a medium refractive index film, a barrier film, and a high refractive index film in this order, wherein the medium refractive index film comprises one or more oxides, nitrides, oxynitrides, and fluorides of a first element, the barrier film comprises one or more oxides, nitrides, oxynitrides, and fluorides of a second element, the thickness of the barrier film is 80 nm or less, the second element comprises one or more silicon and germanium, and the high refractive index film is a silicon film, a germanium film, or a silicon germanium film.

[0050] Another embodiment is an optical filter comprising a substrate and a dielectric multilayer film provided on at least one main surface of the substrate, wherein the dielectric multilayer film is a laminate on the substrate in which one or more layers each of a low refractive index film, a medium refractive index film, and a high refractive index film are laminated, and the dielectric multilayer film is formed such that it has at least one structure in which a low refractive index film, a medium refractive index film, a barrier film, and a high refractive index film are included in this order, wherein the medium refractive index film contains one or more oxides, nitrides, oxynitrides, and fluorides of a first element, the barrier film contains one or more oxides, nitrides, oxynitrides, and fluorides of a second element, the thickness of the barrier film is 80 nm or less, the second element contains one or more silicon and germanium, and the high refractive index film is a silicon film, a germanium film, or a silicon germanium film.

[0051] The present disclosure will be described in further detail below based on examples. Examples 1a and 4 are comparative examples, and Examples 2a, 2, 3 and 5 to 7 are examples. In these examples, the optical properties of an optical filter comprising a substrate and a dielectric multilayer film disposed on the main surface of the substrate were investigated.

[0052] [Study I] (Example 1a) A dielectric multilayer film S1-1 was formed on one main surface of a 1 mm thick silicon substrate, and a dielectric multilayer film S2-1 was formed on the other main surface, both by sputtering. Dielectric multilayer films S1-1 and S1-2 both contained a substructure UA1 which included a high refractive index film, a medium refractive index film, and a low refractive index film in that order away from the substrate, and a substructure UA2 which similarly included a low refractive index film, a medium refractive index film, and a high refractive index film in that order away from the substrate, but each film had a different thickness. In both substructures, Si (hydrogen-undoped amorphous silicon) (refractive index 4.5) was used as the high refractive index film, and Nb was used as the medium refractive index film. ２ O ５ (Refractive index 2.3), SiO as a low refractive index film ２ A refractive index of 1.5 was used.

[0053] Table 1 shows the details of the dielectric multilayer film configuration, namely the total number of films in the dielectric multilayer film, the total number of films of each film type in the dielectric multilayer film (total number of films of each film type), the film thickness of the dielectric multilayer film, the total film thickness of each film type in the dielectric multilayer film (total number of films of each film type), and the film thickness of each component in the substructure, for dielectric multilayer films S1-1 and S2-1 respectively, and also shows the sum of both. As is clear from Table 1, Example 1a was an optical filter equipped with a dielectric multilayer film that did not include a barrier film.

[0054] (Example 2a) Similar to Example 1a, an optical filter was fabricated by forming dielectric multilayer films S1-2 and S2-2 on both sides of a silicon substrate, respectively. However, each of the dielectric multilayer films S1-2 and S2-2 contained a substructure UB1 and a substructure UB2. Both substructure UB1 and substructure UB2 were similar to substructures UA1 and UA2 in that they contained a high refractive index film, a medium refractive index film, and a low refractive index film in that order away from the substrate, but they were substructures that included a barrier film between the high refractive index film and the medium refractive index film. The barrier film was SiO ２ A refractive index of 1.5 was used. Details of the dielectric multilayer films S1-2 and S2-2 are shown in Table 1. As shown in Table 1, the optical filter of Example 2a had a configuration in which a barrier film was added to each of the substructures in the dielectric multilayer film of the optical filter of Example 1a.

[0055] = Examination of Optical Properties = The optical properties were examined using a spectrophotometer (Agilent Technologies, multi-angle variable automatic measurement spectrophotometer "Cary 7000") to measure the maximum transmittance at an incident angle of 0° in the near-infrared region (T800-1600(0)MAX) (%), the minimum reflectance at an incident angle of 60° in the near-infrared region (R800-1600(60)MIN) (%), and the average transmittance at an incident angle of 0° in the visible region (T400-680(0)AVE) (%). The results are shown in Table 2.

[0056] In this embodiment, a maximum transmittance of 90% or more at an incident angle of 0° in the near-infrared region (T800-1600(0)MAX) is considered good, and a minimum reflectance of 2.0% or less at an incident angle of 60° in the near-infrared region (R800-1600(60)MIN) is considered good.

[0057]

[0058]

[0059] As shown in Tables 1 and 2, the optical filter of Example 2a, in which a barrier film was provided between the medium refractive index film and the high refractive index film, showed improved maximum transmittance (%) at an incident angle of 0° in the near-infrared region compared to the optical filter of Example 1a, which did not have a barrier film. Furthermore, the optical filter of Example 2a also suppressed the minimum reflectance (%) at an incident angle of 60° in the near-infrared region compared to the optical filter of Example 1a.

[0060] [Study II] The optical properties of the optical filter were investigated by simulation.

[0061] (Example 2) An optical filter was generated on a computer, having the same lamination configuration as the optical filter in Example 2a in "Consideration I," with a dielectric multilayer film S1-2 on one main surface of a silicon substrate and a dielectric multilayer film S2-2 on the other main surface.

[0062] (Examples 3 and 4) Using the same method as in Example 2, an optical filter was produced in Example 3, which had a dielectric multilayer film S1-3 on one main surface of a silicon substrate and a dielectric multilayer film S2-3 on the other main surface. In Example 4, an optical filter was produced, which had a dielectric multilayer film S1-4 on one main surface of a silicon substrate and a dielectric multilayer film S2-4 on the other main surface.

[0063] Table 3 shows the detailed configuration of the dielectric multilayer film for each example (for Example 2, the stacking configuration of Example 2a is repeated).

[0064] = Examination of Optical Characteristics = For the optical filters of Examples 2 to 4, the maximum transmittance at an incident angle of 0° in the near-infrared region (T800-1600(0)MAX) (%), the minimum reflectance at an incident angle of 60° in the near-infrared region (R800-1600(60)MIN) (%), and the average transmittance at an incident angle of 0° in the visible region (T400-680(0)AVE) (%) were calculated. The results are shown in Table 4.

[0065]

[0066]

[0067] Tables 3 and 4 show that the optical filters in Examples 2 to 4, which have a barrier film between the medium refractive index film and the high refractive index film, all exhibited high maximum transmittance (%) of 90% or more at an incident angle of 0° in the near-infrared region. Furthermore, in Examples 2 and 3, where the barrier film thickness was 80 nm or less, the minimum reflectance (%) at an incident angle of 60° in the near-infrared region was also sufficiently suppressed. However, in Example 4, where the barrier film thickness was 150 nm, the suppression of the minimum reflectance (%) at an incident angle of 60° in the near-infrared region was not sufficiently achieved. In addition, in all examples, the average transmittance (%) at an incident angle of 0° in the visible region was low, indicating a high function of blocking visible light.

[0068] Furthermore, the results of Example 2 (Table 3) are equivalent to those of Example 2a (Table 2) described above, demonstrating that the results obtained from actual measurements correspond to the results obtained from simulations.

[0069] [Study III] The optical properties of the optical filter were investigated by changing the substrate material from the simulation in Study II.

[0070] (Examples 5 to 7) An optical filter was generated on a computer as Example 5, in which a dielectric multilayer film S1-5 was formed on one main surface of a 2 mm thick glass substrate and a dielectric multilayer film S2-5 was formed on the other main surface. Both dielectric multilayer films S1-5 and S1-5 contained a high refractive index film, a medium refractive index film, and a low refractive index film in that order away from the substrate, but had a partial structure including a barrier film between the high refractive index film and the medium refractive index film. Similarly, an optical filter of Example 6 was generated, which had a dielectric multilayer film S1-6 on one main surface of the substrate and a dielectric multilayer film S2-6 on the other main surface, and an optical filter of Example 7 was generated, which had a dielectric multilayer film S1-7 on one main surface of the substrate and a dielectric multilayer film S2-7 on the other main surface. Table 3 shows the details of the dielectric multilayer film configuration for each example.

[0071] = Examination of Optical Characteristics = For the optical filters of Examples 5 to 7, the maximum transmittance (T800-1600(0)MAX) (%) at an incident angle of 0° in the near-infrared region, and the minimum reflectance (R800-1600(60)MIN) (%) at an incident angle of 60° in the near-infrared region were calculated. Furthermore, the average transmittance (T400-680(0)AVE) (%) at an incident angle of 0° in the visible region, and the average reflectance (R400-680(5)AVE) (%) at an incident angle of 5° in the visible region were also calculated. The results are shown in Table 6.

[0072]

[0073]

[0074] Tables 5 and 6 show that, even in Examples 5 to 7 where the substrate material was glass, the optical filters (Examples 5 to 7) with a barrier film between the medium refractive index film and the high refractive index film exhibited high maximum transmittance (%) at an incident angle of 0° in the near-infrared region, and also suppressed the minimum reflectance (%) at an incident angle of 60° in the near-infrared region. Furthermore, the average transmittance (%) at an incident angle of 0° in the visible region was found to be low, at 5% or less.

[0075] Regarding the optical properties in the visible region, in all of Examples 5 to 7, the average reflectance (%) at an incident angle of 5° in the visible region was 10% or less, indicating that the reflection of visible light was sufficiently suppressed. In particular, in Examples 5 and 6, where the barrier film thickness was 40 nm or less, even greater suppression was possible.

[0076] Although the present disclosure has been described above based on embodiments, the present disclosure is not limited to these embodiments. Furthermore, the above embodiments can be modified, altered, replaced, added, deleted, and combined in various ways within the scope of the claims, and these also fall within the technical scope of the present disclosure.

[0077] This application claims priority based on Japanese Patent Application No. 2024-196828, filed on 11 November 2024, and incorporates all of its disclosures herein.

[0078] 1 Optical filter 10 Substrate S, S1, S2 Dielectric multilayer film BR Barrier film H High refractive index film L Low refractive index film M Medium refractive index film

Claims

1. An optical filter comprising a substrate and a dielectric multilayer film provided on at least one main surface of the substrate, wherein the dielectric multilayer film is a laminate in which one or more layers each of a low refractive index film, a medium refractive index film, and a high refractive index film are laminated, the dielectric multilayer film has at least one structure in which the low refractive index film, medium refractive index film, barrier film, and high refractive index film are laminated in that order, the medium refractive index film contains one or more oxides, nitrides, oxynitrides, and fluorides of a first element, the barrier film contains one or more oxides, nitrides, oxynitrides, and fluorides of a second element, the thickness of the barrier film is 80 nm or less, the mean extinction coefficient of the second element is smaller than the mean extinction coefficient of the first element in the wavelength range of 800 to 1600 nm, and the high refractive index film is a silicon film, a germanium film, or a silicon germanium film.

2. An optical filter comprising a substrate and a dielectric multilayer film provided on at least one main surface of the substrate, wherein the dielectric multilayer film is a laminate in which one or more layers of a low refractive index film, a medium refractive index film, and a high refractive index film are laminated, the dielectric multilayer film has at least one structure in which a low refractive index film, a medium refractive index film, a barrier film, and a high refractive index film are laminated in that order, the medium refractive index film contains one or more oxides, nitrides, oxynitrides, and fluorides of a first element, the barrier film contains one or more oxides, nitrides, oxynitrides, and fluorides of a second element, the thickness of the barrier film is 80 nm or less, the second element contains one or more silicon and germanium, and the high refractive index film is a silicon film, a germanium film, or a silicon germanium film.

3. The optical filter according to claim 1 or 2, wherein the maximum transmittance at an incident angle of 0° in the wavelength range of 800 to 1600 nm is 90% or more.

4. The optical filter according to claim 1 or 2, wherein the minimum reflectance at an incident angle of 60° in the wavelength range of 800 to 1600 nm is 2.0% or less.

5. The optical filter according to claim 1 or 2, wherein the dielectric multilayer film is provided on both main surfaces of the substrate.

6. The optical filter according to claim 1 or 2, wherein the average transmittance at an incident angle of 0° in the wavelength range of 400 to 680 nm is 2% or less.

7. The optical filter according to claim 1 or 2, wherein the average extinction coefficient of the second element in the wavelength range of 800 to 1600 nm is 0.01 or less.

8. The optical filter according to claim 1 or 2, wherein the barrier film comprises an oxide of silicon or germanium.

9. The barrier film is SiO ２ An optical filter according to claim 1 or 2, which is a film.

10. The optical filter according to claim 1 or 2, wherein the intermediate refractive index film comprises an oxide of one or more elements: Ta, Nb, Ti, Zr, Hf, and Al.

11. The optical filter according to claim 1 or 2, wherein the high refractive index film is an amorphous silicon film.

12. The optical filter according to claim 1 or 2, wherein the medium refractive index film and the high refractive index film are not in contact.

13. The optical filter according to claim 1 or 2, wherein the thickness of the barrier film is 40 nm or less.

14. The optical filter according to claim 13, wherein the average reflectance at an incident angle of 5° in the wavelength range of 400 to 680 nm is 10% or less.

15. The optical filter according to claim 1 or 2, wherein the maximum transmittance at an incident angle of 0° in the wavelength range of 800 to 1600 nm is 98.2% or more.

16. A near-infrared light sensor module comprising the optical filter described in claim 1 or 2.

17. A method for manufacturing an optical filter comprising a substrate and a dielectric multilayer film provided on at least one main surface of the substrate, comprising forming a dielectric multilayer film on the substrate such that the dielectric multilayer film is a laminate in which one or more layers of a low refractive index film, a medium refractive index film, and a high refractive index film are laminated, the dielectric multilayer film having at least one structure comprising a low refractive index film, a medium refractive index film, a barrier film, and a high refractive index film in this order, the medium refractive index film comprising one or more oxides, nitrides, oxynitrides, and fluorides of a first element, the barrier film comprising one or more oxides, nitrides, oxynitrides, and fluorides of a second element, the thickness of the barrier film being 80 nm or less, the second element comprising one or more silicon and germanium, and the high refractive index film comprising one or more silicon, germanium, and silicon germanium.

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