Multilayer film, optical member, image capturing device, and method of manufacturing multilayer film

Abstract

To provide a multilayer film having superior hydrophilic and photocatalytic properties, and to provide an optical member, an image capturing device, and a method of manufacturing the multilayer film.SOLUTION: A multilayer film to be provided on a substrate, the multilayer film comprising a silicon oxide layer provided with a moth-eye structure on a surface thereof and configured to exhibit hydrophilicity, and a titanium oxide layer disposed in contact with the silicon oxide layer and configured to exhibit a photocatalytic feature.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a multilayer film, an optical member, an imaging device, and a method for manufacturing a multilayer film. [Background technology]

[0002] When water droplets form on the surface of optical components used in cameras and other devices due to condensation, the droplets scatter light, degrading image quality. Furthermore, repeated condensation and drying can leave dirt on the surface of the optical components, which scatters and blocks light, degrading image quality. Dirt also reduces hydrophilicity, making water droplets more likely to form. Removing water droplets and dirt is difficult for optical components placed in enclosed spaces. One solution is to apply a hydrophilic layer to the surface of the optical component to suppress the formation of water droplets, and to apply a photocatalytic layer to decompose organic matter contained in the dirt. It is also desirable for optical components to have a low reflectance to incident light.

[0003] Patent Document 1 discloses a multilayer film having hydrophilic, photocatalytic and low reflectance properties, which includes an antireflection layer on the surface of a substrate, a photocatalytic layer made of titanium oxide on the surface of the antireflection layer, and fine pores made of silicon oxide formed on the surface of the photocatalytic layer. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2020 / 129558 Summary of the Invention [Problem to be solved by the invention]

[0005] An object of the present disclosure is to provide a multilayer film having excellent hydrophilicity and photocatalytic properties, an optical member including the multilayer film, and a method for manufacturing the multilayer film. [Means for solving the problem]

[0006] The multilayer film of the present disclosure is a multilayer film provided on a substrate, the multilayer film including a silicon oxide layer having a moth-eye structure on its surface and exhibiting hydrophilicity, and a titanium oxide layer that exhibits photocatalytic function and is disposed in contact with the silicon oxide layer.

[0007] The titanium oxide layer of the multilayer film of the present disclosure is preferably disposed between the silicon oxide layer and the substrate.

[0008] The silicon oxide layer of the multilayer film of the present disclosure preferably has a functional group that exhibits hydrophilicity.

[0009] The height of the moth-eye structure of the multilayer film of the present disclosure is preferably 120 nm to 400 nm, and the period is preferably 80 nm to 220 nm.

[0010] In the multilayer film of the present disclosure, the thickness of the titanium oxide layer is preferably 250 nm to 500 nm, and the ultraviolet irradiation energy required for photocatalytic activity is 7 J / cm 2 It is preferable that:

[0011] The multilayer film of the present disclosure more preferably has a contact angle of 5° or less. The contact angle of water can be measured using a commercially available contact angle meter. In this specification, the contact angle of water refers to a static contact angle measured with a water droplet of 1 μL.

[0012] The multilayer film of the present disclosure preferably has a haze of 3.2% or less.

[0013] The multilayer film of the present disclosure preferably has an intermediate layer having an anti-reflection function between the substrate and the titanium oxide layer.

[0014] The optical member of the present disclosure includes the multilayer film of the present disclosure and a substrate having the multilayer film provided on a surface thereof, The substrate is an optical member that is a flat plate substrate with a flat surface or an optical lens having a predetermined curvature.

[0015] The optical member of the present disclosure preferably has a reflectance of 0.05% or less when light having a wavelength of 400 nm to 700 nm is incident perpendicularly.

[0016] The imaging device of the present disclosure is an imaging device equipped with the optical member of the present disclosure.

[0017] The method for manufacturing the multilayer film of the present disclosure is a method for manufacturing the multilayer film of the present disclosure. [Effects of the Invention]

[0018] According to the technology of the present disclosure, it is possible to obtain a multilayer film having excellent hydrophilicity and photocatalytic properties, an optical member including the multilayer film, and a method for manufacturing the multilayer film. [Brief explanation of the drawings]

[0019] [Figure 1] FIG. 1 is a cross-sectional view of an optical member according to an embodiment. [Figure 2] FIG. 10 is a schematic cross-sectional view of an optical member according to a modified example. [Figure 3] 1A to 1C are diagrams illustrating a manufacturing process of an optical member according to an embodiment. [Figure 4] 10A to 10C are diagrams showing details of a mask forming step. [Figure 5] FIG. 10 is a diagram showing details of an etching step. [Figure 6] FIG. 1 is a perspective view of an imaging device according to an embodiment. [Figure 7] FIG. 10 is a diagram showing spatial frequency spectra of Samples 1-1 to 1-8. [Figure 8] Figure 8(1A) is an example of a surface SEM image of Sample 1-8, and Figure 8(1B) is an example of a cross-sectional SEM image of Sample 1-8. Figure 8(2A) is an example of a surface SEM image of a sample in which an aluminum oxide film is formed instead of the aluminum nitride film of Sample 1-8, and Figure 8(2B) is an example of a cross-sectional SEM image of a sample in which an aluminum oxide film is formed instead of the aluminum nitride film of Sample 1-8. [Figure 9] FIG. 10 is a diagram showing the average height and average period of irregularities of Samples 2-1 to 2-8 and Samples 3-1 to 3-8. [Figure 10]FIG. 10 is a graph showing the ultraviolet irradiation energy dependence of the photocatalytic activity of Samples 4-1 to 4-5. [Figure 11] FIG. 10 is a graph showing the ultraviolet irradiation energy dependence of the photocatalytic activity of a comparative sample. [Figure 12] FIG. 1 is a diagram showing a change in refractive index of a moth-eye structure. [Figure 13] FIG. 10 is a diagram showing the reflectance of Sample 5-1. [Figure 14] FIG. 10 is a diagram showing the reflectance of Sample 5-4. DETAILED DESCRIPTION OF THE INVENTION

[0020] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. For ease of visualization, the thicknesses and ratios of each layer have been appropriately modified and do not necessarily reflect the actual thicknesses and ratios. In this specification, a numerical range expressed using "to" means a range that includes the numerical values ​​before and after "to" as the lower and upper limits.

[0021] FIG. 1 shows a cross-sectional view of an optical member according to one embodiment. The optical member 1 includes an optical substrate 10 having a flat surface and a multilayer film 3 according to one embodiment. The multilayer film 3 includes a titanium oxide layer 20 provided on the optical substrate 10 and a silicon oxide layer 30 having a moth-eye structure 32 on its surface. In this example, the titanium oxide layer 20 is disposed between the silicon oxide layer 30 and the optical substrate 10. The silicon oxide layer 30 has the moth-eye structure 32 on its surface and exhibits hydrophilicity. The titanium oxide layer has a photocatalytic function. This provides the multilayer film 3 with both hydrophilicity and photocatalytic activity. The water contact angle on the surface of the multilayer film 3 is preferably 10° or less, and more preferably 5° or less. The water contact angle can be measured using a commercially available contact angle meter. In this specification, the water contact angle refers to a static contact angle measured with a 1 μL water droplet.

[0022] The optical substrate 10 is an example of a substrate of the present disclosure. The shape of the optical substrate 10 is not particularly limited, and may be a transparent substrate primarily used in optical devices, such as a flat plate substrate with a flat surface, or an optical lens such as a concave or convex lens having a predetermined curvature, or may be a substrate configured by combining a curved surface having a predetermined positive or negative curvature with a flat surface.

[0023] The titanium oxide layer 20 is preferably a film formed by a vapor phase film formation method. Specifically, the titanium oxide layer 20 is preferably a sputtered film formed by a sputtering method or a vapor deposition film formed by a vapor deposition method. The titanium oxide layer 20 is preferably anatase type.

[0024] When the composition of titanium oxide contained in the titanium oxide layer 20 is expressed as TiOx, it is preferable that 1.90≦x≦2.00, and more preferably 1.95≦x≦2.00.

[0025] The thickness of the titanium oxide layer 20 is 250 nm to 500 nm, and the ultraviolet irradiation energy required for photocatalytic activity is 7 J / cm 2 From the viewpoint of photocatalytic activity, the thickness of the titanium oxide layer 20 is preferably 300 nm or more, more preferably 400 nm or more, and most preferably 500 nm. However, from the viewpoint of the balance between ultraviolet irradiation energy and reflectance, the thickness of the titanium oxide layer 20 is preferably 250 nm to 300 nm.

[0026] The silicon oxide layer 30 has a moth-eye structure 32. In the silicon oxide layer 30, the aluminum content is 0.25 wt.% or less, the calcium content is 2.0 wt.% or less, the boron content is 2.0 wt.% or less, and the carbon content is 6.0 wt.% or less. The aluminum content is preferably 0.1 wt.% or less, the calcium content is preferably 1.0 wt.% or less, the boron content is preferably 1.0 wt.% or less, and the carbon content is preferably 4.0 wt.% or less. The contents of the components contained in the silicon oxide layer 30 can be measured by X-ray photoelectron spectroscopy (XPS).

[0027] When the composition of silicon oxide contained in the silicon oxide layer 30 is expressed as SiOx, it is preferable that 1.90≦x≦2.00, and more preferably 1.95≦x≦2.00.

[0028] The moth-eye structure 32 is a structure including a plurality of convex portions whose cross-sectional area gradually decreases from the bottom surface (substrate side) of the silicon oxide layer 30 toward the surface. In FIG. 1, the moth-eye structure 32 is a structure in which convex portions with triangular cross sections are regularly arranged, but in this specification, the moth-eye structure refers to a structure in which a large number of convex portions with tapered tips are regularly or irregularly arranged. Due to this shape, the moth-eye structure exhibits a refractive index change in which the refractive index gradually decreases from the bottom surface toward the surface, reaching a refractive index of 1, which is approximately the same as that of air, at the outermost surface.

[0029] The average height of the moth-eye structure 32 is preferably 120 nm to 400 nm, and the average period is preferably 80 nm to 220 nm. The average height is more preferably 300 nm or less, and even more preferably 180 nm or less. The average period is still more preferably 130 nm or less.

[0030] The method for measuring the average height and the average period will be explained in the Examples below.

[0031] The silicon oxide layer 30 preferably has functional groups on its surface that exhibit hydrophilicity. It is known that the silicon oxide layer 30 exhibits hydrophilicity because the surface is covered with hydroxyl groups (-OH), which reduces the difference between the surface free energy of water and the surface free energy of the optical member. Furthermore, by forming the surface into a moth-eye structure 32, the surface area per unit space increases compared to a smooth surface, and the concentration of hydroxyl groups per unit space increases. This results in even higher hydrophilicity. Furthermore, by making the gaps between the irregularities of the moth-eye structure 32 large enough to allow water to penetrate, even higher hydrophilicity is exhibited.

[0032] On the other hand, functional groups exhibiting hydrophilicity include, in addition to hydroxyl groups, amino groups, carbonyl groups, carboxyl groups, phenyl groups, methyl groups, etc., and any of these groups may be modified on the surface of the silicon oxide layer 30. Functional groups other than hydroxyl groups can be modified on the surface of the silicon oxide multilayer film by immersing the multilayer film in a liquid substance containing these groups and then performing plasma treatment on the surface of the silicon oxide multilayer film.

[0033] The multilayer film 3 preferably has a haze of 3.2% or less. A smaller haze is more preferable. The smaller the haze of the multilayer film 3, the less scattering occurs within the optical component, and the higher the quality of the optical component. Therefore, the smaller the haze of the multilayer film 3, the more preferable it is. The haze can be measured using a commercially available haze meter.

[0034] As described above, the multilayer film 3 of this embodiment includes a titanium oxide layer 20 provided on the optical substrate 10 and a silicon oxide layer 30 provided on the titanium oxide layer 20 and having a moth-eye structure 32 on its surface. The moth-eye structure 32 on the surface of the silicon oxide layer 30 increases the surface area of ​​the silicon oxide layer 30. As a result, the difference between the surface free energy of water and the surface free energy of the multilayer film 3 decreases. The smaller the difference between the surface free energy of water and the surface free energy of the multilayer film 3, the higher the hydrophilicity of the multilayer film 3. Furthermore, by providing the moth-eye structure 32 on the surface of the silicon oxide layer 30, the surface area can be increased compared to a porous silicon oxide layer or a rhombic silicon oxide layer, resulting in high hydrophilicity. Furthermore, because the silicon oxide layer 30 has the moth-eye structure 32 and the bottom of the concave portions of the concave portions is close to the titanium oxide layer 20, which serves as a photocatalytic layer, active species are generated with low UV energy, thereby increasing the concentration of active species at the outermost surface of the multilayer film 3. In other words, the photocatalytic action of the titanium oxide layer 20 can be achieved with low UV energy.

[0035] In the multilayer film 3 of this embodiment, the silicon oxide layer 30 has an aluminum content of 0.25 wt.% or less, a calcium content of 2.0 wt.% or less, a boron content of 2.0 wt.% or less, and a carbon content of 6 wt.% or less. With this configuration, when fabricating the optical component 1, the generation of compounds that react with the etching gas and inhibit etching can be suppressed during vapor-phase etching of the silicon oxide layer 30. Therefore, the moth-eye structure 32 can be easily formed.

[0036] In addition, when the silicon oxide layer 30 is a film formed by a vapor phase film formation method, for example, a sputtered film or a vapor deposition film formed by a sputtering method or a vapor deposition method, it is possible to make the impurity concentration of the film sufficiently reduced.

[0037] The average height of the moth-eye structures 32 is preferably 120 nm to 400 nm, and when the average period is 80 nm to 220 nm, haze can be suppressed.

[0038] (Variation) FIG. 2 shows a cross-sectional view of a modified optical element 2. In FIG. 2, the same components as those in FIG. 1 are assigned the same reference numerals. The optical element 2 includes an optical substrate 10 and a modified multilayer film 4. The modified multilayer film 4 includes an intermediate layer 12 between the optical substrate 10 and the titanium oxide layer 20, the intermediate layer 12 having an anti-reflection function that reduces the reflectance of incident light. In this specification, the term "intermediate layer" refers to a layer provided between the optical substrate 10 and the titanium oxide layer 20.

[0039] As shown in Fig. 2(a), the intermediate layer 12 is preferably formed by alternately stacking high-refractive-index layers 12a having a relatively high refractive index and low-refractive-index layers 12b having a relatively low refractive index. In Fig. 2(a), the low-refractive-index layers 12b and the high-refractive-index layers 12a are alternately stacked in this order from the optical substrate 10 side, but there is no particular restriction on the number of layers in the multilayer film, and the intermediate layer 12 may have a six-layer structure as shown in Fig. 2(b).

[0040] The high-refractive-index layer 12a has a higher refractive index than the low-refractive-index layer 12b, and the low-refractive-index layer 12b has a lower refractive index than the high-refractive-index layer 12a. However, it is more preferable that the refractive index of the high-refractive-index layer 12a is higher than the refractive index of the optical substrate 10, and the refractive index of the low-refractive-index layer 12b is lower than the refractive index of the optical substrate 10.

[0041] The high refractive index layers 12a and the low refractive index layers 12b do not have to have the same refractive index, but it is preferable to use the same material and have the same refractive index in order to reduce material costs, film formation costs, and the like.

[0042] Examples of materials that can be used to form the high refractive index layer 12a include niobium pentoxide (Nb2O5), titanium oxide (TiO2), zirconium oxide (ZrO2), tantalum pentoxide (Ta2O5), silicon oxynitride (SiON), silicon nitride (Si3N4), and silicon niobium oxide (SiNbO).

[0043] Examples of materials that can be used to form the low refractive index layer 12b include silicon oxide (SiO2), silicon oxynitride (SiON), gallium oxide (Ga2O3), aluminum oxide (Al2O3), lanthanum oxide (La2O3), lanthanum fluoride (LaF3), magnesium fluoride (MgF2), and sodium aluminum fluoride (Na3AlF6).

[0044] The refractive index of any compound can be changed to some extent by forming a film by controlling the ratio of constituent elements so as to deviate from the stoichiometric composition ratio or by controlling the film formation density.

[0045] The multilayer film 4 also functions as an anti-reflection film by including the intermediate layer 12 having an anti-reflection function. The multilayer film 4 preferably has an average reflectance of 0.1% or less, more preferably 0.05% or less for wavelengths of 400 nm to 700 nm.

[0046] The optical element 2 provided with the multilayer film 4 preferably has an average reflectance of 0.1% or less, and more preferably 0.05% or less, when light having a wavelength of 400 nm to 700 nm is incident perpendicularly to the substrate surface. The average reflectance refers to the average value of the reflectance at each wavelength within the wavelength range of 400 nm to 700 nm. The lower the reflectance, the higher the anti-reflection performance.

[0047] The reflectance for each wavelength is measured by irradiating light onto the optical member 2 at an incident angle of 5°. The wavelength dependency of the reflectance can be measured using a commercially available spectrometer.

[0048] The moth-eye structure 32 on the surface of the silicon oxide layer 30 has a refractive index that gradually decreases in the film thickness direction from the optical substrate 10 side toward the surface side (see, for example, FIG. 12). Such a change in refractive index has the effect of preventing reflection of light incident from the surface side, and the synergistic effect of the moth-eye structure 32 and the intermediate layer 12 provides a remarkable anti-reflection effect.

[0049] (Manufacturing method) A method for manufacturing the optical member 1, including a method for manufacturing the multilayer film 3 according to one embodiment, will be described.

[0050] 3, the method for manufacturing the optical member 1 includes steps A to C. Step A is a step of forming a titanium oxide layer 20 and a silicon oxide layer 30 on an optical substrate 10. Step B is a mask formation step of forming a mask 40 on the silicon oxide layer 30. Step C is an etching step of vapor-phase etching the silicon oxide layer 30 using the mask 40 and an etching gas G.

[0051] In the film formation step (step A), a titanium oxide layer 20 and a silicon oxide layer 30 are sequentially formed on one surface of the optical substrate 10 by a vapor phase film formation method. Examples of vapor phase film formation methods include sputtering, vacuum deposition, and chemical vapor deposition, with sputtering being particularly preferred. By using the vapor phase film formation method, it is possible to prevent impurities from being mixed into the titanium oxide layer 20 and the silicon oxide layer 30. In other words, a sputtered film formed by a sputtering method or a vapor deposition film formed by a vacuum deposition method can be said to be a film in which the mixing of elements other than the target (i.e., impurities) is sufficiently prevented.

[0052] When the silicon oxide layer 30 is formed by sputtering, an SiO2 target is used, oxygen is introduced into the film formation chamber, and the x of silicon oxide (SiOx) can be adjusted arbitrarily by adjusting the flow rate of the oxygen.

[0053] The thickness of the titanium oxide layer 20 is, for example, 250 nm to 500 nm. The silicon oxide layer 30 has a thickness of, for example, 500 nm to 1500 nm.

[0054] The details of the mask formation step (step B) are shown in Fig. 4. As an example, the mask formation step includes, as shown in Fig. 4, step B-1: an Al-containing thin film formation step of forming a thin film 42 containing aluminum (hereinafter referred to as Al-containing thin film 42) on the silicon oxide layer 30, and step B-2: a hot water treatment step of treating the Al-containing thin film 42 with hot water.

[0055] In the Al-containing thin film forming step (step B-1), the Al-containing thin film 42 is formed by a vapor deposition method. Examples of vapor deposition methods include sputtering, vacuum deposition, and chemical vapor deposition, with sputtering being particularly preferred. When the silicon oxide layer 30 is formed by sputtering, it is preferable to form the Al-containing thin film 42 continuously in the same chamber.

[0056] Examples of the Al-containing thin film 42 include an aluminum film, an aluminum oxide film, and an aluminum nitride film. The thickness of the Al-containing thin film 42 is preferably 10 nm to 40 nm. It is particularly preferable to use an aluminum nitride film.

[0057] The hot water treatment in the hot water treatment step (step B-2) refers to a treatment in which the laminate is exposed to hot water of 60°C or higher for 20 seconds or more. Examples of hot water treatment include a method of immersing the laminate on which the Al-containing thin film 42 has been formed in room temperature water (especially pure water is preferred) and then boiling the water, a method of immersing the laminate in hot water maintained at a high temperature, or a method of exposing the Al-containing thin film 42 to high-temperature steam. In this embodiment, pure water 6 contained in a water tank 5 is heated, and the laminate consisting of the optical substrate 10, the titanium oxide layer 20, the silicon oxide layer 30, and the Al-containing thin film 42 is immersed in the heated pure water 6 for the hot water treatment. The boiling or immersion time is particularly preferably 3 minutes or more and 15 minutes or less. The temperature of the hot water is preferably higher than 90°C. The higher the temperature, the shorter the treatment time tends to be.

[0058] The hot water treatment transforms the Al-containing thin film 42 into a concave-convex structure layer whose main component is alumina hydrate, as shown in step B-3. The concave-convex structure layer corresponds to the mask 40. Hereinafter, the term "convex-convex structure layer 40" is synonymous with the mask 40. The alumina hydrate that constitutes the concave-convex structure layer 40 includes boehmite (written as Al2O3·H2O or AlOOH), which is an alumina monohydrate, and bayerite (written as Al2O3·3H2O or Al(OH)3), which is an alumina trihydrate (aluminum hydroxide).

[0059] The concave-convex structure layer 40 has a concave-convex structure in which the height and period of the concaves and convexes are random, and the size (size of the apex angle) and direction of the convex portions vary, but the cross section is generally sawtooth-shaped.

[0060] Details of the etching step (step C) are shown in Fig. 5. As an example, the etching step includes step C-1: a physical etching step in which the concave-convex structure layer 40 is physically etched according to its shape, and step C-2: a reactive etching (chemical etching) step in which the silicon oxide layer 30 exposed in the recesses of the concave-convex structure layer 40 is selectively etched, as shown in Fig. 5.

[0061] In the physical etching step (step C-1), the concave-convex structure layer 40 made of alumina hydrate is etched to expose the silicon oxide layer 30 in the recesses of the concave-convex structure layer 40. Here, as the etching gas G1, for example, a mixed gas of argon (Ar) and CHF3 (trifluoromethane) is used. The physical etching time is preferably, for example, about 15 to 60 seconds, and more preferably 30 to 45 seconds.

[0062] In the chemical etching step (step C-2), the silicon oxide layer 30 exposed in the recesses is etched. For example, a mixed gas of SF6 (sulfur hexafluoride) and CHF3 is used as the etching gas G2. In this case, the reactive gas SF6 reacts with SiO2 to generate and vaporize SiF4, which chemically etches the SiO2. In this chemical etching step, etching is performed until the distance d2 from the surface of the silicon oxide layer 30 facing the optical substrate 10 to the apex of the largest convexity of the moth-eye structure becomes smaller than the film thickness d1 of the silicon oxide layer 30 immediately after deposition. The chemical etching time is preferably, for example, 1 to 35 minutes, more preferably 1 to 25 minutes, and particularly preferably 10 to 25 minutes.

[0063] After the chemical etching step, a cleaning step (step C-3) is carried out to remove the uneven structure layer 40 remaining on the surface of the silicon oxide layer 30.

[0064] In the cleaning process (process C-3), the concave-convex structure layer 40 is removed using SH3O3 (a mixed solution of sulfuric acid and hydrogen peroxide), dried, and then irradiated with ultraviolet (UV) light. The UV irradiation is performed to decompose unnecessary organic matter that has been mixed in during the manufacturing process. In a manufacturing environment where the amount of contamination can be ignored, UV irradiation is not essential.

[0065] Through the above steps, the optical member 1 can be produced.

[0066] When fabricating an optical component 2 including the intermediate layer 12 and the titanium oxide layer 20, the intermediate layer 12 and the titanium oxide layer 20 are formed before the silicon oxide layer 30 is formed on the optical substrate 10. It is also preferable to use a vapor phase deposition method for forming the intermediate layer 12 and the titanium oxide layer 20. Vapor phase deposition makes it easy to form layered structures with a variety of refractive indices and layer thicknesses.

[0067] When performing the above-described chemical etching, if the silicon oxide layer 30 contains impurity elements that react with the etching gas to form compounds that are difficult to gasify, this may inhibit the reaction between SiO2 and the reactive gas. If the reaction between SiO2 and the reactive gas is inhibited, problems such as a slow or unstable etching rate or etching stall may occur. Examples of impurity elements that react with SF6 to form fluorine compounds that are difficult to gasify include aluminum, calcium, boron, and carbon. As described above, forming the silicon oxide layer 30 by a vapor-phase deposition method such as sputtering using an SiO2 target can sufficiently suppress the inclusion of these impurity elements compared to liquid-phase deposition methods such as sol-gel deposition, thereby eliminating the problem of etching inhibition during the chemical etching process.

[0068] Furthermore, optical substrates used in cover glasses, lenses, and the like may contain metals other than Si (e.g., Al, Ca) for purposes such as lowering the softening point or adjusting the refractive index. Therefore, if an attempt is made to directly form a concave-convex structure on the surface of an optical element by etching the surface of the optical substrate, the above-mentioned problems may arise in the chemical etching step of step C-2, which may result in a long time required for forming the concave-convex structure or may result in an insufficient depth of the concave-convex structure. In the manufacturing method for the optical element 1, since a silicon oxide layer 30 is formed on the optical substrate 10, it is not a problem even if the optical substrate 10 contains impurity elements, and the method can be applied regardless of the material of the optical substrate 10.

[0069] The above-mentioned optical members 1 and 2 are highly hydrophilic and have a high self-cleaning function, and are therefore suitable as optical members arranged in areas prone to condensation, such as optical lenses of endoscope cameras, surveillance cameras, and vehicle-mounted cameras.

[0070] An imaging device according to an embodiment of the present disclosure will be described. FIG. 6 is a perspective view showing the appearance of a camera 130, which is an imaging device according to an embodiment of the present disclosure. The camera 130 is a so-called mirrorless digital camera, to which an interchangeable lens 120 can be removably attached. The interchangeable lens 120 includes a zoom lens housed in a lens barrel. For example, an optical element 101 according to an embodiment of the present disclosure is applied to the outermost lens among the optical lenses constituting the zoom lens. The optical element 101 includes a multilayer film 103 according to an embodiment of the present disclosure on the surface exposed to the outside.

[0071] Camera 130 includes camera body 131, and a shutter button 132 and a power button 133 are provided on the top surface of camera body 131. An operation unit and a display unit are also provided on the back surface (not shown) of camera body 131. The display unit can display a captured image and an image within the angle of view before capture.

[0072] A photographic opening through which light from the subject to be photographed enters is provided in the center of the front of the camera body 131, and a mount 137 is provided at a position corresponding to the photographic opening, and an interchangeable lens 120 is attached to the camera body 131 via the mount 137.

[0073] Inside the camera body 131, there are provided an imaging element such as a CCD (Charge Coupled Device) or a CMOS (Complementary Metal Oxide Semiconductor) that outputs an imaging signal corresponding to the subject image formed by the interchangeable lens 120, a signal processing circuit that processes the imaging signal output from the imaging element to generate an image, and a recording medium for recording the generated image. [Example]

[0074] Samples of examples and comparative examples of multilayer films and optical members were prepared and various tests were carried out to verify the multilayer films and optical members of the present disclosure. The results will be described below.

[0075] In preparing the samples used in each test, an RF magnetron sputtering device BMS-800II (Shinchron Co., Ltd.) was used as the film deposition device. The film deposition conditions for each film will be described later.

[0076] The properties of each sample were measured by the following methods.

[0077] (Water contact angle) A contact angle meter (DM300, Kyowa Interface Science Co., Ltd.) was used to measure the water contact angle. Here, static contact angles were measured using a 1 μL water droplet. While hydrophilicity is measured in this specification using the contact angle of water, it may also be measured using the contact angle of a liquid other than water. For example, the contact angle may be measured using n-hexadecane or ethylene glycol instead of water to evaluate hydrophilicity. A liquid with a surface free energy lower than that of water (72.8 mN / m) may also be used for contact angle measurement. More specifically, if the dispersive component of the surface energy of the liquid used exhibits a value close to that of water, hydrophilicity can be evaluated using the same contact angle relationship as that of water. The values ​​of the dispersive component of the liquid used can be those described in Japanese Patent Publication No. 4012891.

[0078] (average height of unevenness) The average height of the irregularities is the average height from the bottom of the recesses to the top of the protrusions of the fine irregular structure (moth-eye structure) formed on the surface of the silicon oxide layer, and was calculated as follows. First, the cross section of the optical component was photographed at 50,000x magnification using a scanning electron microscope (SEM) to obtain an SEM image. The SEM image was then binarized to detect the edges of the uneven structure, and a fill process was performed to fill in the recesses, noise was removed, and the boundary between the unevenness and the air on the surface of the unevenness was determined. These processes allowed the boundary line of the unevenness to be determined, with the deepest position being set to a height of 0. The average height of the unevenness can be determined by integrating and averaging the unevenness height within the boundary line thus determined.

[0079] (average period of unevenness) The average period was calculated by obtaining the spatial frequency spectrum, determining the spatial frequency value at which the maximum intensity was obtained, and then calculating the period from this spatial frequency value. Specifically, a planar SEM image of the fine uneven structure (moth-eye structure) was obtained at a magnification of 10,000 times using a scanning electron microscope, and a 1000 x 680 pixel range was cut out from the SEM image and subjected to a two-dimensional Fourier transform. The squared intensity spectrum of the obtained two-dimensional spatial frequency was integrated in the azimuthal direction, and the spectral intensity corresponding to the magnitude of the spatial frequency was calculated to calculate the relationship between the one-dimensional spatial frequency and the spectral intensity (see Figure 7). The spatial frequency value at which the maximum intensity (peak) was obtained was then determined by fitting the vicinity of the vertex with a Gaussian function. For example, if the spatial frequency value showing the maximum intensity is 5 μm, -1 , the period [μm] is 1 / 5=0.2, and the average period is 200 nm.

[0080] (Hayes) The haze was measured using a haze meter (SH7000: Nippon Denshoku Industries Co., Ltd.). Haze [%] = (diffuse transmitted light amount / (normal transmitted light amount + diffuse transmitted light amount)) x 100 The greater the haze, the greater the amount of diffused transmitted light.

[0081] (Image evaluation method) Each sample was attached as a lens filter to a general-purpose portable TV camera (main body: Sony HDC-4300, lens: Fujinon UA18x7.6BERD), and the subject was photographed. The photographed image was displayed on a monitor. The photographed image was subjected to a sensory evaluation based on the following evaluation criteria. A: The haze is not noticeable at all. You can get a clear image (black part). B: Unless you look at the image carefully, you won't notice the scattering. C: The level at which the effect of scattering can be seen in the image. D: The black parts of the image are clearly affected by scattering, making them appear white.

[0082] (Photocatalytic activity dependence on ultraviolet irradiation energy (WAX test)) Car wax (trade name "New Willson" manufactured by Willson) was rubbed onto the sample surface using a cotton swab. After 24 hours or more had passed since the wax application, the wax applied to the sample surface was removed with a neutral detergent and water, and the contact angle θ1 of the sample surface with water after the wax was removed was measured. The sample surface was then irradiated with ultraviolet light, and after the irradiation, the contact angle θ2 of the sample surface with water was measured again. The ultraviolet light source used was a UV-B ultraviolet lamp 20WGL20SE manufactured by Sankyo Electric, and the irradiation conditions were a UV illuminance of 3 mw / cm. 2 The irradiation time was 0.5 to 42 minutes. 2 The contact angle measurement device used was a DM300 manufactured by Kyowa Interface Science.

[0083] (Refractive index of film) Measurement was carried out by ellipsometry (JA Woolam VASE).

[0084] "Test 1" Mask samples 1-1 to 1-8 were prepared as optical substrates each having a silicon oxide layer and a moth-eye structure made of an aluminum nitride film on the surface of the silicon oxide layer. Sample 1-8 was also etched to produce samples 2-1 to 2-8 each having a moth-eye structure made of a silicon oxide layer, and various evaluations were performed on these samples.

[0085] (Sample production method) Samples 1-1 to 1-8 were prepared as follows. A white plate substrate (B270i: manufactured by SCHOTT) with a diameter of 80 mm and a thickness of 2 mm was used as the optical substrate. A silicon oxide layer of 1000 nm was formed on this white plate substrate by sputtering, and an aluminum nitride film of 10 nm or 40 nm was further formed by sputtering. Next, the white plate substrate with the silicon oxide layer and aluminum nitride film laminated thereon was subjected to a hot water treatment in which it was immersed in hot water at 80°C or 100°C for 20 seconds or 3 minutes. This converted the aluminum nitride film into a finely textured layer composed of alumina hydrate. The aluminum nitride film thickness, hot water treatment temperature, and immersion time for each of Samples 1-1 to 1-8 are shown in Table 1 below.

[0086] The silicon oxide layer was formed using an SiO2 target, and the aluminum nitride film was formed using an Al target. The sputtering conditions were as follows:

[0087] -Sputtering conditions for silicon oxide layer- Target input power: 500W Vacuum level: 0.2 Pa, O2 atmosphere (O2 flow rate: 200 sccm) No substrate heating

[0088] -Sputtering conditions for aluminum nitride film- Target input power: 600W Vacuum level: 0.2 Pa, N2 atmosphere (N2 flow rate: 150 sccm) No substrate heating

[0089] For Samples 1-1 to 1-8 prepared as described above, the sample preparation conditions and the measurement results of the height and period of the concave-convex structure are shown in Table 1. Furthermore, Fig. 7 shows the spatial frequency spectra (relationship between spatial frequency and spectral intensity) of Samples 1-1 to 1-8. The reciprocal of the spatial frequency showing the intensity peak of the spatial frequency spectrum shown in Fig. 7 was calculated as the concave-convex period.

[0090] [Table 1]

[0091] As shown in Table 1, the height and period of the micro-irregularity layer formed can be changed by varying the aluminum nitride film thickness, the hot water treatment temperature, and the immersion time. For each of Samples 1-1 to 1-8, the haze was very small, at 0.18% or less. When the silicon oxide layer is etched using the micro-irregularity layer as a mask, the irregularities of the micro-irregularity layer are transferred to the silicon oxide layer. In other words, a moth-eye structure with an irregularity period corresponding to the irregularity period of the micro-irregularity layer of the mask is formed in the silicon oxide layer. A multilayer film with a moth-eye structure silicon oxide layer obtained by etching using a mask with a low haze is expected to have a low haze.

[0092] For mask sample 1-8, an etching process was performed using the fine concave-convex layer as a mask, and samples 2-1 to 2-8 with a moth-eye structure made of a silicon oxide layer were produced. The etching process first involved physical etching, followed by chemical etching. The concave portions of the fine concave-convex layer were penetrated by physical etching to expose the silicon oxide layer. Then, the silicon oxide layer exposed in the concave portions of the fine concave-convex layer was etched by chemical etching. The conditions for physical etching and chemical etching were as follows:

[0093] -Physical etching conditions- ICP (Inductively Coupled Plasma) output: 300W, bias output: 120W Etching pressure: 3Pa Etching gas: Ar (100 sccm), CHF3 (10 sccm) Substrate temperature: 10℃ Etching time: 45 seconds.

[0094] - Chemical etching conditions - ICP output: 500W, bias output: 15W Etching pressure: 0.6 Pa Etching gas: SF6 (40sccm), CHF3 (40sccm) Substrate temperature: 10℃ Etching time: 1 to 35 minutes (varies depending on the sample) The etching times for each of Samples 2-1 to 2-8 are shown in Table 2 below.

[0095] Table 2 shows the chemical etching time, haze measurement results, image sensory evaluation results, water contact angle measurement results, unevenness height measurement results, and unevenness period measurement results for Samples 2-1 to 2-8.

[0096] [Table 2]

[0097] In this test 1, the results of the sensory evaluation using the image evaluation method indicated that a haze of 3.2% or less is desirable, 1.5% or less is even more desirable, and 0.44% or less is the most desirable. Although low haze and a small water contact angle are inversely related, it was confirmed that a range in which both low haze (haze of 3.2% or less) and a small water contact angle (contact angle of 5° or less) are achieved exists when the unevenness height is 120 nm to 300 nm and the unevenness period is 80 nm to 220 nm. It was also confirmed that haze tends to decrease as the unevenness height and unevenness period become smaller.

[0098] "Test 2" In the above Samples 1-1 to 1-8, aluminum nitride was used as the mask material. In contrast, Sample A was prepared using aluminum oxide as the mask material and compared with the case where aluminum oxide was used. Specifically, Sample A was prepared by depositing an aluminum oxide film instead of the aluminum nitride film in Sample 1-8 to form a fine uneven layer. Sample A was prepared by depositing an aluminum oxide film with a thickness of 40 nm and performing hot water treatment under the same conditions as Sample 1-8. That is, the hot water treatment conditions for Sample A were a hot water treatment temperature of 100°C and an immersion time of 180 seconds. Figure 8 (1A) is a surface SEM image of Sample 1-8, and Figure 8 (1B) is a cross-sectional SEM image of Sample 1-8. Figure 8 (2A) is a surface SEM image of Sample A, and Figure 8 (2B) is a cross-sectional SEM image.

[0099] 8(1A) to (2B) show that when hot water treatment is performed under the same conditions, both the height and period of the irregularities of an aluminum nitride film are smaller than those of an aluminum oxide film. Specifically, the fine irregularity layer of Sample 1-8 had an irregularity period of 86 nm and an irregularity height of 176 nm, while the fine irregularity layer of Sample A had an irregularity period of 300 nm and an irregularity height of 280 nm. Furthermore, the haze of Sample A was approximately 3% to 5%, which was significantly larger than that of Samples 1-1 to 1-8.

[0100] Furthermore, Sample A (a sample in which aluminum oxide was used instead of aluminum nitride in Sample 1-8) was etched under the same conditions as Samples 2-1 to 2-8 to produce Samples 3-1 to 3-8. The asperity height and asperity period of Samples 3-1 to 3-8 were also measured in the same manner as Samples 2-1 to 2-8. Figure 9 is a graph showing the dependence of the moth-eye structure on the mask material. Samples 2-1 to 2-8, which are aluminum nitride film masks, and Samples 3-1 to 3-8, which are aluminum oxide film masks, are plotted on a graph with the asperity period (the moth-eye asperity period in Figure 9) on the vertical axis and the asperity height (the moth-eye asperity height in Figure 9) on the horizontal axis. Figure 9 shows that, when comparing samples with the same asperity height, the asperity period is smaller when an aluminum nitride film is used as the mask material.

[0101] From the results of Tests 1 and 2, when a finely textured layer made of alumina hydrate is used as a mask in producing the multilayer film of the present disclosure, it is considered preferable to use aluminum nitride rather than aluminum oxide as the mask material from the viewpoint of suppressing haze.

[0102] "Test 3" A plurality of samples 4-1 to 4-5 were prepared with different thicknesses of the titanium oxide layer, and the photocatalytic function was evaluated. Samples 4-1 to 4-5 were produced by forming a titanium oxide layer having a thickness shown in Table 3 on an optical substrate, and then forming a silicon oxide layer having a moth-eye structure. The conditions for producing the silicon oxide layer having the moth-eye structure for Samples 4-1 to 4-5 were the same as those for Sample 2-4.

[0103] [Table 3]

[0104] The results of measuring the dependency of photocatalytic activity on ultraviolet irradiation energy (wax test) for Samples 4-1 to 4-5 are shown in Figure 10. The vertical axis in Figure 10 is the water contact angle θ2 measured after ultraviolet irradiation on the sample surface. For Samples 4-1 to 4-5, the water contact angle before the wax test was generally 5° or less, and the contact angle θ1 in the wax test was all around 60°. The smaller θ2 means a higher self-cleaning effect. For Samples 4-1 to 4-5, the titanium oxide layer was 300 nm or less, and the ultraviolet irradiation energy was 2 J / cm 2 It was confirmed that when the contact angle θ2 of water is less than 5°, a highly efficient self-cleaning effect is achieved.

[0105] Comparative samples were prepared by forming a titanium oxide layer and a silicon oxide layer on a whiteboard substrate. The comparative samples did not have a moth-eye structure on the surface of the silicon oxide layer, but instead had a silicon oxide layer with a smooth surface. Comparative samples were prepared with a fixed titanium oxide layer thickness of 300 nm and silicon oxide film thicknesses of 10 nm, 20 nm, 40 nm, 80 nm, and 100 nm, and a wax test was performed. Figure 11 shows the results of measuring the dependence of photocatalytic activity on UV irradiation energy for the comparative samples. The water contact angle of each comparative sample before the wax test was approximately 5° to 10°, and the contact angle θ1 after the wax test was approximately 60°. For the silicon oxide layer with a smooth surface, the thickness was 10 nm to 20 nm, and the UV irradiation dose was 6.5 J / cm. 2With the above, the water contact angle θ2 can be made 10° or less, the film thickness is 10 nm, and the ultraviolet irradiation amount is 7.0 J / cm 2 By doing this, the water contact angle θ2 could be reduced to about 5°. It was found that in the case of the comparative sample, a larger amount of UV irradiation was required to achieve a sufficient self-cleaning effect. It was also found that the thicker the silicon oxide layer, the less the photocatalytic function of the titanium oxide layer could be exerted.

[0106] A comparison of Figures 10 and 11 clearly shows that by providing a silicon oxide film with a moth-eye structure on its surface, it is possible to effectively exert the photocatalytic function of the titanium oxide layer provided underneath.

[0107] "Test 4" Samples 5-1 to 5-6 of optical members having a multilayer film including an intermediate layer, such as the optical member 2 shown in FIG. 2, were prepared and evaluated for their photocatalytic function and antireflection function. Sample 5-1 is a titanium oxide layer (TiO 2-x ) and silicon oxynitride layer (SiO x N y After forming an intermediate layer consisting of layers of titanium dioxide and titanium dioxide, a titanium oxide layer that exhibits photocatalytic function was formed, and then a silicon oxide layer (SiO2 moth-eye) with a moth-eye structure was formed. The conditions for forming the silicon oxide layer with a moth-eye structure were the same as those for Sample 2-4 described above. The layer structure of Sample 5-1 is shown in Table 4. Layers No. 3 and 4 are intermediate layers, and Layer No. 2 is a titanium oxide layer that exhibits photocatalytic function.

[0108] [Table 4]

[0109] In Sample 5-2, the thickness of the titanium oxide layer exhibiting photocatalytic function, Layer No. 2, of Sample 5-1 was changed to 250 nm, and in Sample 5-3, the thickness of the titanium oxide layer exhibiting photocatalytic function, Layer No. 2, of Sample 5-1 was changed to 500 nm.

[0110] Sample 5-4 had a structure in which, instead of the intermediate layer of Sample 5-1, an intermediate layer was provided, consisting of a total of six alternately stacked titanium oxide layers and silicon oxynitride layers. The layer structure of Sample 5-4 is shown in Table 5. Layers 3 to 8 are intermediate layers, and Layer 2 is a titanium oxide layer that exhibits photocatalytic function.

[0111] [Table 5]

[0112] Sample 5-5 was obtained by changing the thickness of the photocatalytic titanium oxide layer No. 2 of Sample 5-4 to 250 nm, and Sample 5-6 was obtained by changing the thickness of the photocatalytic titanium oxide layer No. 2 of Sample 5-4 to 500 nm.

[0113] Figure 12 shows the refractive index distribution of the moth-eye structure of a silicon oxide layer. The refractive index of the silicon oxide layer with the moth-eye structure varies between 1 and 1.46. The refractive index of the silicon oxide layer is highest on the optical substrate side and lowest on the surface side where light from outside the optical substrate is incident. In addition, the amount of change in refractive index per unit length from the optical substrate side to the surface side is very small. This type of refractive index distribution results in excellent wavelength band characteristics and incident angle characteristics of reflectance.

[0114] The reflectance of each sample was measured by the following method.

[0115] (reflectance) The reflectance was measured using a microspectrophotometer (USPM-PU: Olympus Optical Co., Ltd.) The reflectance for each wavelength was measured when light was incident on the optical member at an incident angle of 5° (vertical incidence).

[0116] The measurement results of the reflectance of Sample 5-1 are shown in Figure 13. The measurement results of the reflectance of Sample 5-4 are shown in Figure 14. By combining the moth-eye structure and the intermediate layer, an optical component with extremely good anti-reflection properties was obtained.

[0117] The various evaluation results for Samples 5-1 to 5-6 are shown in Table 6. A thin photocatalyst layer made of titanium oxide can reduce the average reflectance, but the contact angle with water after the wax test is large, which is thought to reduce the self-cleaning effect. The photocatalyst layer with a thickness of 300 nm provided the best balance of properties.

[0118] [Table 6]

[0119] The following additional notes are provided regarding the above-described embodiments. (Appendix 1) A multilayer film provided on a substrate, a silicon oxide layer having a moth-eye structure on its surface and exhibiting hydrophilicity; a titanium oxide layer that exhibits a photocatalytic function and is disposed in contact with the silicon oxide layer; Multilayer film. (Appendix 2) The titanium oxide layer is disposed between the silicon oxide layer and the substrate. 1. The multilayer film according to claim 1. (Appendix 3) The silicon oxide layer has functional groups that exhibit hydrophilicity. 10. The multilayer film according to claim 1 or 2. (Appendix 4) The height of the moth-eye structure is 120 nm to 400 nm, The period is 80nm~220nm, 4. The multilayer film according to any one of claims 1 to 3. (Appendix 5) The thickness of the titanium oxide layer is 250 nm to 500 nm, The UV irradiation energy required for photocatalytic activity is 7J / cm 2 Below is the 5. The multilayer film according to any one of claims 1 to 4. (Appendix 6) 6. The multilayer film according to any one of claims 1 to 5, wherein the multilayer film has a water contact angle of 5° or less. (Appendix 7) 7. The multilayer film according to any one of claims 1 to 6, having a haze of 3.2% or less. (Appendix 8) an intermediate layer having an anti-reflection function between the substrate and the titanium oxide layer; 8. The multilayer film according to any one of claims 1 to 7. (Appendix 9) A multilayer film according to any one of Supplementary Notes 1 to 8; a substrate having a multilayer film formed on a surface thereof; An optical member, wherein the substrate is an optical substrate having a flat surface or an optical lens having a predetermined curvature. (Appendix 10) 10. The optical member according to claim 9, which has a reflectance of 0.05% or less when light having a wavelength of 400 nm to 700 nm is incident perpendicularly. (Appendix 11) An imaging device comprising the optical member according to claim 9 or 10. (Appendix 12) A method for producing a multilayer film according to any one of Supplementary Note 1 to Supplementary Note 9, comprising: a film-forming step of sequentially forming a titanium oxide layer and a silicon oxide layer on an optical substrate by a sputtering method; a mask forming step of forming a fine uneven layer made of alumina hydrate on the surface of the silicon oxide layer; and an etching step of etching the silicon oxide layer using the fine concave-convex layer as a mask. [Explanation of symbols]

[0120] 1, 2 Optical components 3, 4 Multilayer film 5. Aquarium 6 Pure water 10 Optical board 12 Middle Class 12a High refractive index layer 12b Low refractive index layer 20 Titanium oxide layer 30 silicon oxide layer 32 Moth-eye structure 40 Concave-convex structure layer (mask) 42 Al-containing thin film 101 Optical components 103 Multilayer film 120 interchangeable lenses 130 Camera 131 Camera Body 132 Shutter button 133 Power button 137 Mount

Claims

1. A multilayer film provided on a substrate, a silicon oxide layer having a moth-eye structure on its surface and exhibiting hydrophilicity; a titanium oxide layer that exhibits a photocatalytic function and is disposed in contact with the silicon oxide layer, Multilayer film.

2. The titanium oxide layer is disposed between the silicon oxide layer and the substrate. The multilayer film according to claim 1 .

3. The silicon oxide layer has a functional group that exhibits hydrophilicity. The multilayer film according to claim 1 .

4. the height of the moth-eye structure is 120 nm to 400 nm; The period is 80 nm to 220 nm. The multilayer film according to claim 1 .

5. The thickness of the titanium oxide layer is 250 nm to 500 nm, The ultraviolet irradiation energy required for photocatalytic activity is 7 J / cm 2 Below is the The multilayer film according to claim 1 .

6. 2. The multilayer film according to claim 1, wherein the contact angle of water is 5° or less.

7. 10. The multilayer film of claim 1, having a haze of 3.2% or less.

8. an intermediate layer having an anti-reflection function is provided between the substrate and the titanium oxide layer; The multilayer film according to claim 1 .

9. The multilayer film according to any one of claims 1 to 8, the substrate having the multilayer film formed on its surface, The optical member, wherein the substrate is a flat plate substrate having a flat surface or an optical lens having a predetermined curvature.

10. 10. The optical element according to claim 9, wherein the reflectance of light having a wavelength of 400 nm to 700 nm when incident perpendicularly is 0.05% or less.

11. An imaging device comprising the optical member according to claim 9.

12. The method for producing the multilayer film according to claim 1 .

Images