WO2019240040A1

WO2019240040A1 - Method for producing optical element and optical element

Info

Publication number: WO2019240040A1
Application number: PCT/JP2019/022740
Authority: WO
Inventors: 多田一成; 粕谷仁一
Original assignee: コニカミノルタ株式会社
Priority date: 2018-06-14
Filing date: 2019-06-07
Publication date: 2019-12-19
Also published as: JPWO2019240040A1; JP7335556B2

Abstract

Provided are a method for producing an optical element capable of achieving both superhydrophilicity and a photocatalytic effect and also having saltwater resistance, and an optical element produced by the method. A method for producing an optical element 100 in which two or more multilayer films MC are formed on a glass substrate GL which is a light-transmitting substrate, the multilayer film MC including at least one low-refractive-index layer L and at least one high-refractive-index layer H, the method comprising: an uppermost layer formation step of forming a low-refractive-index layer L having salt water spray resistance and superhydrophilicity as an uppermost layer 10 farthest from the glass substrate GL; a functional layer formation step of forming a high-refractive-index layer H mainly composed of a metal oxide having a photocatalytic function as a functional layer 20 under the uppermost layer 10; a mask formation step of forming a metal mask 50 on a surface 10a of the uppermost layer 10 after the uppermost layer formation step; and a through hole formation step of forming a plurality of through holes 30 for exposing the surface of the functional layer 20 in the uppermost layer 10 by etching.

Description

Optical element manufacturing method and optical element

The present invention relates to an optical element manufacturing method in which a multilayer film is formed and an optical element manufactured by the method.

For example, in-vehicle cameras are mounted on vehicles for driving support of vehicles. More specifically, a camera that captures the back and sides of the vehicle is mounted on the body of the automobile, and the image captured by the camera is displayed at a position where the driver can visually recognize it. Contributes to safe driving.

By the way, in-vehicle cameras are often mounted outside the vehicle, and dirt such as water droplets or mud often adheres on the lens. Depending on the degree of water drops and dirt adhering to the lens, the image captured by the camera may become unclear. In view of this, a technique has been developed in which a photocatalytic substance is applied to the object side surface of a lens to clean organic substances adhering to the surface by ultraviolet irradiation. For example, it is conceivable to apply Ti nanoparticles having a photocatalytic effect on the object side surface of an imaging lens mounted on a vehicle-mounted camera.

Patent Document 1 discloses an antireflection article having antireflection properties in which a film having reduced reflectance and having self-cleaning properties is formed without impairing the photocatalytic performance of the photocatalytic particles. The antireflection article of Patent Document 1 includes a fine uneven layer made of resin, an inorganic layer made of SiO ₂ , and a photocatalyst layer made of TiO _{2 on} one surface of a transparent substrate, and the surface of the photocatalyst layer is fine. It has irregularities.

By the way, since an imaging lens or the like mounted on a vehicle-mounted camera is used in a harsh environment, sufficient environmental resistance is required. More specifically, there is a possibility that the exposed optical surface of the imaging lens may be damaged or eroded by impacts, wind pressure, and sand dust splashed by traveling. Furthermore, there is a risk of surface deterioration or alteration due to chemicals such as detergents and waxes used in salt water, acid rain, car washing, etc. contained in the sea breeze.

However, the antireflective article of Patent Document 1 achieves all of the photocatalytic effect, saltwater resistance, hydrophilicity, low reflection characteristics, and scratch resistance functions required for a lens for an in-vehicle camera as described above. Not. Specifically, in the antireflective article of Patent Document 1, the TiO ₂ layer is provided on the top and has a photocatalytic effect. The TiO ₂ layer has a moth-eye structure to reduce the reflectance. However, salt water resistance and hydrophilicity are weak. Further, the antireflection article of Patent Document 1 may be broken in structure by rubbing and has low scratch resistance.

JP 2014-71323 A

An object of the present invention is to provide a method for producing an optical element that can achieve both superhydrophilicity and a photocatalytic effect and also has saltwater resistance, and an optical element produced by the method.

In order to achieve at least one of the objects described above, an optical element manufacturing method reflecting one aspect of the present invention is an optical element manufacturing method in which two or more multilayer films are formed on a light-transmitting substrate. The multilayer film has at least one low-refractive index layer and at least one high-refractive index layer, and has low salt spray resistance and super hydrophilicity as the uppermost layer farthest from the substrate. The uppermost layer forming step for forming the refractive index layer, the functional layer forming step for forming a high refractive index layer mainly composed of a metal oxide having a photocatalytic function as a functional layer under the uppermost layer, and the uppermost layer forming step Thereafter, a mask forming step of forming a metal mask on the surface of the uppermost layer and a through hole forming step of forming a plurality of through holes that expose the surface of the functional layer in the uppermost layer by etching are provided. Here, the low refractive index layer means a layer having a refractive index of 1.7 or less. The high refractive index layer means a layer having a refractive index of 1.9 or more. Moreover, having salt water tolerance means that the film thickness reduction value is 20 nm or less after the salt water spray test described later. Also, having super hydrophilicity means that the contact angle of 10 μl of water droplets on the optical element is 15 ° or less. In the above, for convenience of explanation, the uppermost layer forming step and the functional layer forming step are described in this order, but actually, the uppermost layer forming step is performed after the functional layer forming step.

In order to realize at least one of the above objects, an optical element reflecting one aspect of the present invention is manufactured by the above-described optical element manufacturing method, and has an island-shaped through hole structure in the uppermost layer.

It is a figure which shows typically the cross section of the optical element concerning this embodiment. FIG. 2A is a diagram schematically showing a cross section of an optical element manufactured by forming a particulate metal mask, and FIG. 2B is a schematic cross section of an optical element manufactured by forming an island metal mask. 2C is a SEM image of the surface of the uppermost layer in FIG. 2B, and FIG. 2D is a diagram schematically showing a cross section of an optical element formed by forming a porous metal mask. . It is a figure explaining the manufacturing method of an optical element. 4A to 4C are conceptual diagrams for explaining a process of forming a through-hole by forming a particulate metal mask in an optical element manufacturing method, and FIG. 4D is an example in which an island-shaped metal mask is formed. FIG. 4E is a conceptual diagram illustrating an example in which a porous metal mask is formed. FIG. 5A is an SEM image of a sample on which a particulate metal mask is formed, FIG. 5B is an SEM image showing a state where through holes are formed by etching the sample of FIG. 5A, and FIG. 5C is an island shape FIG. 5D is an SEM image of a sample on which a porous metal mask is formed. 6A to 6C are views in which the SEM images of the optical element whose uppermost layer is processed into an island shape are enlarged step by step.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a diagram schematically showing a cross section of an optical element according to the present embodiment. An optical element 100 shown in FIG. 1 is a multilayer film MC having a structure in which low refractive index layers L and high refractive index layers H are alternately laminated on a glass substrate (glass substrate) GL which is a substrate having light transmittance. It is what has. The low refractive index layer L means a layer having a refractive index of 1.7 or less. The high refractive index layer H means a layer having a refractive index of 1.9 or more. The glass substrate GL is not limited to a flat plate and may include a lens. However, the high refractive index layer H may be in contact with the glass substrate GL. Such an optical element 100 can be used as an in-vehicle lens or a communication lens. In FIG. 1, the layer located between the glass substrate GL and the functional layer 20 may be replaced with an equivalent film of an intermediate refractive index layer instead of a high refractive index layer or a low refractive index layer.

In FIG. 1, the uppermost layer 10 farthest from the glass substrate GL is a low refractive index layer L, and a high refractive index layer H provided below the uppermost layer 10, which is adjacent to the uppermost layer 10 in this embodiment. The high refractive index layer H is a metal oxide functional layer 20 having a photocatalytic function. By using the low refractive index layer L having a relatively high strength as the uppermost layer 10, scratch resistance can be improved. Moreover, since the functional layer 20 exhibits a photocatalytic function using active oxygen excited by UV light through or through the uppermost layer 10, the functional layer 20 is preferably placed as close as possible to the uppermost layer 10. By providing the functional layer 20 adjacent to the uppermost layer 10, for example, a photocatalytic function can be effectively exhibited. In addition, by using a metal oxide having a photocatalytic effect and a photoactive effect as the functional layer 20, surface organic substances can be removed and the super hydrophilicity of the uppermost layer 10 can be maintained. For the functional layer 20, for example, TiO ₂ or the like is used. When the functional layer 20 using TiO ₂ is formed using IAD (Ion Assisted Deposition (hereinafter referred to as IAD)), the photocatalytic effect is enhanced.

“Photocatalytic function” refers to the strong oxidizing power generated by the incidence of sunlight or artificial light, which effectively removes toxic substances such as organic compounds and bacteria that come in contact, It refers to a self-cleaning function such as preventing the oil from staying on the surface and washing with water or the like without fixing oily stains, such as titanium dioxide. Note that “adjacent to the uppermost layer” means that the function is not hindered between the uppermost layer 10 and the functional layer 20 in addition to the case where the uppermost layer 10 and the functional layer 20 are in close contact with each other. This includes the case where a layer (for example, a layer of 20 nm or less) is provided.

As shown in FIGS. 2A to 2D, the low refractive index layer L of the uppermost layer 10 has a plurality of through holes 30 for causing the functional layer 20 to be the adjacent high refractive index layer H to exhibit a photocatalytic function. . Although details will be described later, the through hole 30 is formed by dry etching. The ratio of the total cross-sectional area of the plurality of through holes 30 to the surface area of the low refractive index layer L of the uppermost layer 10 (the total area of the through holes 30 when the optical element 100 is viewed from above) (hereinafter referred to as the through hole density or For example, when the through hole 30 is formed using an island-shaped metal mask 50 described later, the film drop-off rate is about 50%. Moreover, the cross section of the through-hole 30 has a random shape.

In addition, the optical element 100 of the present embodiment desirably satisfies the following conditional expression.
10 nm ≦ TL ≦ 350 nm (1)
50 nm ≦ Tcat ≦ 700 nm (2)
here,
TL: film thickness of uppermost layer 10 Tcat: film thickness of high refractive index layer H or functional layer 20 adjacent to uppermost layer 10

When the value of conditional expression (1) is not more than the upper limit, the photocatalytic effect can be exhibited by exchanging active oxygen excited by UV light through the plurality of through holes 30 provided in the uppermost layer 10. On the other hand, if the value of conditional expression (1) is equal to or greater than the lower limit, the superhydrophilic function of the uppermost layer 10 can be easily maintained and a strong uppermost film can be formed, so that sufficient scratch resistance can be secured. The optical element 100 preferably satisfies the following formula.
50 nm ≦ TL ≦ 250 nm (1 ′)

If within the range of conditional expression (1 '), it is easy to keep the reflectance within 2%. Further, when the value of the conditional expression (1 ′) is less than or equal to the upper limit, the photocatalytic function of the functional layer 20 is easily expressed on the outermost surface of the functional layer 20.

When the value of conditional expression (2) is equal to or greater than the lower limit, the film thickness of the functional layer 20 can be ensured, so that a sufficient photocatalytic effect can be expected. On the other hand, as the thickness of the functional layer 20 increases, the photocatalytic effect can be expected. However, since it becomes difficult to obtain desired spectral characteristics required for the multilayer film, the value of the conditional expression (2) is less than the upper limit. It is desirable to do. The optical element 100 preferably satisfies the following formula.
50 nm ≦ Tcat ≦ 600 nm (2 ′)

The high refractive index layer H or the functional layer 20 adjacent to the uppermost layer 10 is formed of an oxide (for example, TiO ₂ ) whose main component is Ti. Ti oxides such as TiO ₂ have a very high photocatalytic effect. In particular, anatase TiO ₂ is desirable as a material for the functional layer 20 because of its high photocatalytic effect.

The uppermost layer 10 is a layer having salt spray resistance and super hydrophilicity, and is mainly formed of, for example, SiO ₂ . Having salt spray resistance means that the film thickness reduction value is 20 nm or less after the salt spray test described below. Moreover, having super hydrophilicity means that the contact angle of 10 μl of water droplets on the optical element 100 is 15 ° or less. The uppermost layer 10 preferably contains 90% or more of SiO ₂ . UV light is hard to be incident at night or outdoors, and the hydrophilic effect is reduced with an oxide mainly composed of Ti, but even in such a case, the superhydrophilic effect can be exhibited by forming the top layer 10 from SiO _2. In addition, the scratch resistance is further improved. When SiO ₂ is used for the uppermost layer 10, scratch resistance is improved by performing a heat treatment at 500 ° C. for 2 hours after film formation.

The uppermost layer 10 may be formed of a mixture of SiO ₂ and Al ₂ O ₃ (however, the composition ratio of SiO ₂ is 90% by weight or more). Thereby, a hydrophilic effect can be exhibited even at night or outdoors, and scratch resistance is further enhanced by using a mixture of SiO ₂ and Al ₂ O ₃ . When a mixture of SiO ₂ and Al ₂ O ₃ is used for the uppermost layer 10, scratch resistance is improved by performing a heat treatment at 200 ° C. or higher for 2 hours after film formation. It is preferable to use the IAD method when a part or all of the uppermost layer 10 is formed. Thereby, the scratch resistance is improved.

Each layer of the multilayer film MC is formed by an evaporation method, and any one of the layers is preferably formed by an IAD method. Scratch resistance can be further improved by film formation by the IAD method.

In particular, the uppermost layer 10 is formed by an IAD method, a chemical vapor deposition (CVD) method, a sputtering method, or the like.

The film density of the low refractive index layer L which is the uppermost layer 10 is 98% or more. Here, the film density means the space filling density. By setting the film density of the low refractive index layer L of the uppermost layer 10 to 98% or more, resistance to salt water (that is, salt spray resistance) can be further improved.

The optical element 100 preferably satisfies the following conditional expression.
1.35 ≦ NL ≦ 1.55 (3)
here,
NL: Refractive index at the d-line of the material of the low refractive index layer L

By satisfying conditional expression (3), an optical element 100 having desired optical characteristics can be obtained. Here, the d line means light having a wavelength of 587.56 nm. As a material for the low refractive index layer L, SiO ₂ having a refractive index of 1.48 at d-line or MgF ₂ having a refractive index of 1.385 at d-line can be used.

The optical element 100 preferably satisfies the following conditional expression.
1.6 ≦ Ns ≦ 2.2 (4)
here,
Ns: Refractive index at d line of glass substrate GL

In optical design, by satisfying conditional expression (4) as the refractive index at the d-line of the glass substrate GL, the optical performance of the optical element 100 can be enhanced after having a compact configuration. By forming the multilayer film MC of the present embodiment on the glass substrate GL satisfying the conditional expression (4), it can be used for a lens exposed to the outside world, and has excellent environmental resistance and optical performance. It can be compatible.

Hereinafter, a method for manufacturing the optical element 100 will be described with reference to FIG. First, the low refractive index layer L and the high refractive index layer H as the multilayer film MC are alternately laminated on the glass substrate (glass substrate) GL (multilayer film forming step: step S11). However, in step S11, a layer excluding the uppermost layer 10 and the functional layer 20 is formed in the multilayer film MC. That is, the layers up to the low refractive index layer L adjacent to the lower side of the functional layer 20 are formed. The multilayer film MC is formed using various vapor deposition methods, IAD methods, sputtering methods, and the like. Depending on the configuration of the optical element 100, the formation of the multilayer film MC in step S11 may be omitted.

Next, the high refractive index layer H to be the functional layer 20 is formed on the multilayer film formed in step S11 (functional layer forming step: step S12). The high refractive index layer H as the functional layer 20 is formed using various vapor deposition methods, IAD methods, sputtering methods, and the like. The high refractive index layer H as the functional layer 20 is formed of a material mainly containing a metal oxide having a photocatalytic function (specifically, an oxide mainly containing Ti such as TiO ₂ ). When obtaining anatase-type TiO ₂ having a strong photocatalytic effect, it is desirable to form a film at a temperature of 200 ° C. or higher by using an IAD method or a sputtering method.

Next, the low refractive index layer L to be the uppermost layer 10 is formed on the functional layer 20 (uppermost layer forming step: step S13). The low refractive index layer L as the uppermost layer 10 is formed using any one of the IAD method, the CVD method, and the sputtering method. The low refractive index layer L as the uppermost layer 10 is formed of SiO ₂ or a mixture of SiO ₂ and Al ₂ O ₃ . In order to enhance the salt spray resistance, the functional layer 20 is formed under the condition that the film density is 98% or more. In order to obtain the uppermost layer 10 having a film density of 98% or more, it is desirable to form a film at a temperature of 200 ° C. or more by using an IAD method or a sputtering method. By the above, the intermediate body 40 (the thing in which the through-hole 30 is not formed in the uppermost layer 10) which formed multilayer film MC on the glass base material GL is formed.

After the uppermost layer forming step, a metal mask 50 is formed on the surface 10a of the uppermost layer 10 (mask forming step: step S14). As shown in FIGS. 4A and 5A, the metal mask 50 is formed in a particle shape on the surface 10 a of the uppermost layer 10. Thereby, a nano-sized metal mask 50 can be formed on the uppermost layer 10. As shown in FIGS. 4D and 5C, the metal mask 50 may be formed in an island shape. Further, as shown in FIGS. 4E and 5D, the metal mask 50 may be formed in a porous shape. The metal mask 50 includes a metal part 50a and an exposed part 50b. The film thickness of the metal mask 50 is 1 nm or more and 30 nm or less. Although it depends on the film forming conditions, for example, when the metal mask 50 is formed so as to have a film thickness of 2 nm by using an evaporation method, the metal mask 50 is likely to be in the form of particles. Further, when the metal mask 50 is formed to have a film thickness of 12 nm to 15 nm by using, for example, a vapor deposition method, the metal mask 50 tends to have an island shape. Furthermore, if the film thickness is 10 nm using, for example, a sputtering method, the metal mask 50 tends to be porous. By forming the metal thinly in the above-mentioned range, the optimum metal mask 50 in the form of particles, islands, or porous can be easily formed. The metal mask 50 is made of, for example, Ag or Al.

Next, a plurality of through holes 30 are formed in the low refractive index layer L of the uppermost layer 10 (through hole forming step: step S15). As shown in FIGS. 4B and 5B, dry etching using an etching apparatus (not shown) is used for etching. Alternatively, a film forming apparatus used for forming the multilayer film MC or the metal mask 50 may be used. In the through hole forming step, a plurality of through holes are formed using the material of the uppermost layer 10, specifically, a gas that reacts with SiO ₂ . In this case, SiO _{2 of the} uppermost layer 10 can be removed without damaging the metal mask 50. As the etching gas, for example, CHF ₃ , CF ₄ , SF ₆ or the like is used. As a result, a plurality of through holes 30 exposing the surface of the functional layer 20 in the uppermost layer 10 are formed. That is, the uppermost layer 10 corresponding to the exposed portion 50b of the metal mask 50 is etched to form the through holes 30, and the surface of the functional layer 20 is partially exposed.

After the through hole forming process, as shown in FIG. 4C, the metal mask 50 is removed (mask removing process: step S16). Specifically, the metal mask 50 is removed by wet etching using acetic acid or the like. Further, the metal mask 50 may be removed by dry etching using Ar or O ₂ as an etching gas, for example. If the etching of the metal mask 50 is performed using dry etching, a series of steps from the formation of the multilayer film MC to the etching of the metal mask 50 can be performed in the same film forming apparatus.

Through the above steps, the optical element 100 having the plurality of through holes 30 in the uppermost layer 10 can be obtained.

According to the method for manufacturing an optical element described above, after forming the uppermost layer 10, by forming the plurality of through holes 30 for expressing the photocatalytic function in the functional layer 20, both super hydrophilicity and the photocatalytic function are achieved. be able to. The through hole 30 is of a size that allows the functional layer 20 to exhibit a photocatalytic function, is not visually recognized by the user, and has resistance to salt water.

Although the functional layer 20 exhibits a photocatalytic function, since it is the high refractive index layer H, in order to maintain the antireflection characteristics of the optical element 100, the uppermost layer 10 that is the low refractive index layer L on the functional layer 20. It is necessary to provide. Therefore, when the density of the uppermost layer 10 is high, there is a problem that the photocatalytic function of the functional layer 20 is not expressed. On the other hand, when the film density of the uppermost layer 10 is lowered, there is a problem that the salt water resistance and scratch resistance of the uppermost layer 10 are lowered. Like the optical element 100 according to the present embodiment, by providing a plurality of through holes 30 in the uppermost layer 10, the photocatalytic function of the functional layer 20 is exhibited while maintaining antireflection properties, super hydrophilicity, and scratch resistance. be able to.

As described above, the optical element 100 has a multilayer film having anti-reflection properties and excellent salt water resistance and scratch resistance, and can exhibit super hydrophilicity and a photocatalytic effect. Or it is used suitably for building materials.

(Example)
(1) Conditions for forming the uppermost layer through-hole and evaluation of the optical element Specific examples of the optical element 100 according to this embodiment will be described below. In forming the multilayer films of the following examples and comparative examples, a film forming apparatus (BES-1300) (manufactured by Syncron Co., Ltd.) was used, and NIS-175 was used as an IAD ion source.

A nine-layer multilayer film was formed on a glass substrate by heating at 370 ° C. by vapor deposition or IAD to prepare a sample. More specifically, as shown in Table 1, on a glass substrate TAFD5G (manufactured by HOYA Co., Ltd .: refractive index 1.835), a low refractive index layer using SiO ₂ , OA600 (manufactured by Canon Optron Co., Ltd.). A high refractive index layer using a material and a functional layer using TiO ₂ were stacked in the order shown in Table 1 to form a film. As the uppermost layer, SiO ₂ , MgF ₂ , or L5 (manufactured by Merck Ltd.) was used. Table 1 shows the film formation recipe and film configuration of each layer (the layer in contact with the glass substrate (glass substrate) is the first layer). Here, each film thickness (d (nm)) was made constant, and the film formation rate RATE (Å / SEC) of each film was also made constant.

OA 600 in Table 1 is a mixture of Ta ₂ O ₅ , TiO and Ti ₂ O ₅ , and the specific composition thereof is mainly composed of tantalum oxide as shown in Table 2.

L5 in Table 1 is a mixture of SiO ₂ and Al ₂ O ₃ , and the specific composition is as shown in Table 3.

The refractive index in Table 1 is calculated by depositing each layer of the multilayer film MC as a single layer and performing reflectance measurement by a method used for evaluation of antireflection characteristics described later. Using a thin film calculation software (Essential 率 Macleod) (Sigma Koki Co., Ltd.), the refractive index of the film obtained by adjusting the refractive index so as to fit the measured reflectance data is specified.

The film formation prescription is as shown in Table 1, but the formation conditions of the through holes in the uppermost layer were changed, and Examples 1 to 11 (Samples 1 to 11) and Comparative Examples 1 to 3 (Samples 12 to 14) Samples were prepared and subjected to the following tests. The film density of the uppermost layer was set to 98% or more in order to provide salt spray resistance. For Sample 14 of Comparative Example 3, an uppermost layer was not provided and the entire functional layer was exposed. The heating temperature was 370 ° C. and the starting vacuum was 3.00E-03 Pa (3.00 × 10 ⁻³ Pa).

Here, “APC” means that the partial pressure is adjusted by an abbreviation of “Auto Pressure Control”, and “SCCM” is an abbreviation of “standard cc / min”, which is 1 atm (atmospheric pressure 1013 hPa) and 1 at 0 ° C. This is a unit indicating how many cc per minute.

Table 4 below shows the evaluation results of samples 1 to 13 having different formation conditions for the uppermost layer through-holes (including “scrubbing” (scratch resistance evaluation) including sample 14).

Regarding the “photocatalytic effect”, a sample colored with a pen was irradiated with 20 J in total with UV irradiation in an environment of 20 ° C. and 80%, and the color change of the pen was evaluated stepwise. Specifically, The visualiser (manufactured by inkintelligent) was used as a pen. Here, when the color change degree is large (or the color disappears), the photocatalytic effect is sufficient, and the evaluation is indicated with a sign “O”, and when the color change degree is medium (or the color becomes light), the photocatalytic effect remains. As a result, the evaluation was represented by a symbol Δ, and the evaluation with a symbol “x” was regarded as having no photocatalytic effect if the color change degree was minimal (or the color did not disappear).

The “salt water resistance” was evaluated by performing a salt spray test using a salt dry / wet combined cycle tester (CYP-90) (manufactured by Suga Test Instruments Co., Ltd.). In the test, the following steps (a) to (c) were made one cycle, and eight cycles were performed.
(A) A sample having a salt water concentration of 5% at 25 ± 2 ° C. (NaCl, MgCl ₂ , CaCl ₂ , concentration (weight ratio) 5% ± 1%) at a spray layer temperature of 35 ° C. ± 2 ° C. Spray for 2 hours.
(B) After spraying, the sample is left for 22 hours in an environment of 40 ° C. ± 2 ° C. and 95% RH.
(C) Steps (a) and (b) are repeated four times, and then the sample is left for 72 hours in an environment of normal temperature (20 ° C. ± 15 ° C.) and normal humidity (45% RH to 85% RH).
After the above test, if the spectral characteristics of the sample are not changed (reflectance change is less than 2%), the evaluation is a sign ◯, and if the reflectance change is less than 4%, the evaluation is a sign Δ, and the reflectance change is In the case of 4% or more, the evaluation was made as x.

For the “contact angle” (superhydrophilicity evaluation), a contact angle measuring device (G-1) (manufactured by Elma Co., Ltd.) was used to drop 10 μl of water droplets on the sample, and the contact angle was measured. If the contact angle is 15 ° or less, it can be evaluated as having super hydrophilicity.

For “reflectance” (antireflection characteristic evaluation), the reflectance of the sample was evaluated with a maximum reflectance in a wavelength range of 420 nm to 670 nm using a reflectance measuring device (USPM-RUIII) (manufactured by Olympus Corporation). Here, when the reflectance was 5% or less, it was determined that the film had antireflection characteristics, and when the reflectance was over 5%, it was determined that the film had no antireflection characteristics.

For “scouring rub” (scratch resistance evaluation), a reciprocating rub test was performed 250 times with a load of 2 kg using a turtle scourer. Here, when the reflectance change of the sample is less than 2%, the evaluation is indicated by a symbol ◯, and when the reflectance change is 2% or more, the evaluation is indicated by a symbol ×.

As shown in Table 4, when the thickness of the metal mask was 1 nm or more and 30 nm or less, evaluation of the photocatalytic effect, salt water resistance, super hydrophilicity, antireflection property, and scratch resistance was improved. In addition, by providing the uppermost layer on the optical element, it can be seen that the result of the scratching test is good and the optical element has scratch resistance. In Comparative Example 1, when the thickness of the metal mask was 31 nm, the through hole did not reach the surface of the functional layer and the photocatalytic function was not sufficiently exhibited, so that the evaluation of the photocatalytic effect was poor. In Comparative Example 2, the thickness of the metal mask was thin, the exposed portion of the metal mask was increased, and the through hole density of the uppermost layer was too high, resulting in poor evaluation of super hydrophilicity and reflectance.

(2) SEM Image of Optical Element FIGS. 6A to 6C show SEM images of the optical element. 6B is an enlarged view of the image of FIG. 6A, and FIG. 6C is an enlarged view of the image of FIG. 6B.

In this example, the metal mask was formed of Ag using a sputtering method. In this sample, the thickness of the TiO ₂ layer was 282.2 nm, the thickness of the SiO ₂ layer was 87.2 nm, and the thickness of the Ag layer was 10 nm. In the through hole forming step, the uppermost SiO ₂ was dry-etched for 90 seconds. CHF ₃ was used as an etching gas. After the through hole forming step, a mask removing step was performed.

As shown in FIG. 6C and the like, a deep hole was formed in the uppermost layer by the through hole forming step, and the area of the hole also increased. Further, as in the above-described example, as a result of evaluating the photocatalytic function, the photocatalytic function of this sample was maintained. That is, it can be said that the through-hole reaches the surface of the functional layer, the surface of the functional layer is exposed, and the photocatalytic function is exhibited.

The optical element and the manufacturing method thereof as specific embodiments have been described above, but the manufacturing method of the optical element according to the present invention is not limited to the above. For example, in the above embodiment, the metal mask 50 is formed of Ag or Al, but may be formed of other metals as long as it can form a particulate, island, or porous thin film.

In the above embodiment, the film thicknesses of the uppermost layer 10 and the functional layer 20 are not limited to the ranges of the conditional expressions (1) and (2), but can be appropriately changed according to the optical design such as antireflection.

In the above embodiment, the multilayer film MC may include a metal film or a dielectric multilayer film that reflects one or more of visible light and near-infrared light. In this case, the optical element has reflection characteristics. Here, “reflection characteristics” means that the reflectance of light in the visible region or near infrared region is 70% or more, and desirably 85% or more. When a metal film is used, it is preferable that any one of Ag, Au, Cr, Al, Cu, and Ni is a main component. By using these appropriately, the usable area and the reflectance can be arbitrarily adjusted. “Main component” means that the content of the element is 51% by weight or more, preferably 70% by weight or more, more preferably 90% by weight, and still more preferably 100% by weight.

In the above embodiment, at least one of the high refractive index layers H may be formed of a specific material mainly containing any one of Ti, Ta, Hf, Zr, and Nb. Examples of substances that are effective in improving acid resistance include Ti, Ta, Hf, Zr, and Nb oxides. “Main component” means that the content of the element is 51% by weight or more, preferably 70% by weight or more, more preferably 90% by weight, and still more preferably 100% by weight. Since the multilayer film has sufficient acid resistance by using a material mainly composed of Ta, Hf, Zr, and Nb and having an appropriate film thickness, the multilayer film can also be provided on the glass substrate GL that is weak against acid.

Claims

A method of manufacturing an optical element in which a multilayer film having two or more layers is formed on a substrate having optical transparency,
The multilayer film has at least one low refractive index layer and at least one high refractive index layer,
A top layer forming step of forming the low refractive index layer having salt spray resistance and super hydrophilicity as the top layer farthest from the substrate;
A functional layer forming step for forming the high refractive index layer mainly composed of a metal oxide having a photocatalytic function as a functional layer under the uppermost layer;
After the uppermost layer forming step, a mask forming step of forming a metal mask on the surface of the uppermost layer;
A through hole forming step of forming a plurality of through holes exposing the surface of the functional layer in the uppermost layer by etching;
An optical element manufacturing method comprising:
The method of manufacturing an optical element according to claim 1, wherein the metal mask is formed on the surface of the uppermost layer in one of a particle shape, an island shape, and a porous shape.
The method of manufacturing an optical element according to any one of claims 1 and 2, wherein the thickness of the metal mask is 1 nm or more and 30 nm or less.
The optical element manufacturing according to any one of claims 1 to 3, wherein a film density of the low refractive index layer as the uppermost layer formed in the uppermost layer forming step is 98% or more. Method.
The top layer is mainly formed by SiO 2, method of manufacturing an optical element according to any one of claims 1 to 4.
The method for manufacturing an optical element according to claim 5, wherein, in the through hole forming step, the plurality of through holes are formed using a gas that reacts with SiO 2 .
The method for manufacturing an optical element according to any one of claims 1 to 6, further comprising a mask removing step of removing the metal mask after the through hole forming step.
The method of manufacturing an optical element according to any one of claims 1 to 7, wherein the metal mask is made of Ag.
Manufactured by the method for producing an optical element according to any one of claims 1 to 8,
An optical element having an island-shaped through hole structure in the uppermost layer.