JP2013019929A - Anti-reflection coating and anti-reflection coating deposition method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an anti-reflection coating having high scratch resistance through forming a MgFthin film by a sputtering method while maintaining a reflectance characteristic free from trouble in actual use.SOLUTION: An anti-reflection coating includes a porous SiOlayer having a refraction index of 1.34-1.44 at wavelength 500 nm and a MgFlayer with a film thickness of 5-50 nm, formed adjacent to a surface of the porous SiOlayer farther from a substrate. The anti-reflection coating deposition method includes a first process for setting a deposition pressure to be 0.5-10 Pa and depositing SiOby sputtering, and a second process for depositing MgFon the SiOdeposited at the first process, by sputtering granular MgFof a grain size 0.1-10 mm as a target in an Ogas atmosphere.

Description

  The present invention relates to an antireflection film and a method for forming an antireflection film.

  Conventionally, when an optical thin film such as an antireflection film, a half mirror, or an edge filter is manufactured, a vacuum deposition method has been mainly used from the viewpoints of easiness of the method and film formation speed. On the other hand, the sputtering method has many advantages such as automation, labor saving, applicability to a large area substrate, and high adhesion to the substrate, and has been widely applied in the recent coating field.

Here, as a typical low refractive index material for the optical thin film, a fluoride such as MgF ₂ can be cited. When MgF _{2 is formed} by sputtering, it is dissociated into Mg and the like and F, and since F is insufficient in the film, there is a disadvantage that absorption of visible light occurs. It was a major obstacle to application.

  On the other hand, Patent Document 1 describes a thin film forming method in which a fluoride film having no light absorption is formed by a sputtering method. The fluoride thin film produced by this forming method has no practical problem in terms of light absorption.

Japanese Patent No. 3808117 JP-A-8-292302

However, the fluoride thin film produced by the forming method described in Patent Document 1 has high scratch resistance when the produced MgF ₂ film is as thin as about 50 nm, but is necessary for the outermost layer of the multilayer antireflection film. When the film thickness was about 100 nm, there was a problem that the scratch resistance was lowered and scratches were easily generated.

On the other hand, Patent Document 2 describes a method of forming SiO ₂ or Al ₂ O ₃ as a surface protective layer on the MgF ₂ layer in order to improve scratch resistance. However, the film thickness of the surface protective layer is required to be 30 nm or more in order to exert the effect as the surface protective layer in more severe use, for example, use under the condition of a load of 500 gf / cm ^2. The reflectance characteristic as an antireflection film is deteriorated.
In addition, since SiO ₂ and Al ₂ O ₃ used as the surface protective layer have a low water repellency compared to MgF ₂ , cloudiness due to moisture and a shift in reflection characteristics are likely to occur.

The present invention has been made in view of the above-described circumstances, and forms an MgF ₂ thin film by a sputtering method, and maintains a reflectance characteristic that has no practical problem, and has high scratch resistance and antireflection. The object is to provide a membrane.

In order to solve the above-described problems and achieve the object, the antireflection film according to the present invention includes a porous SiO ₂ layer having a refractive index of 1.34 to 1.44 at a wavelength of 500 nm, and a porous SiO ₂ layer substrate. And an MgF ₂ layer having a thickness of 5 to 50 nm formed so as to be adjacent to a distant surface.

The film forming method according to the present invention includes a first step of the SiO ₂ deposited by sputtering by setting the film formation pressure to 0.5～10Pa, on the SiO ₂ was deposited in the first step, the particle size 0. And a second step of sputtering MgF ₂ in an O ₂ gas atmosphere using 1 to 10 mm granular MgF ₂ as a target.

An antireflection film and an antireflection film forming method according to the present invention include forming an MgF ₂ thin film by a sputtering method and maintaining an antireflection film having high scratch resistance while maintaining a reflectance characteristic that is not problematic in practice. There is an effect that it can be provided.

3 is a cross-sectional view showing a layer structure of a multilayer antireflection film according to Example 1. FIG. It is a graph which shows the optical characteristic of the antireflection film of Example 1 and Comparative Examples 1-3. It is the table | surface which compared the characteristic of the antireflection film of Example 1 and Comparative Examples 1-3. It is a graph which shows the optical characteristic of the antireflection film of Example 2 and Comparative Examples 4-6. It is the table | surface which compared the characteristic of the antireflection film of Example 2 and Comparative Examples 4-6.

Embodiments of an antireflection film and a method for forming an antireflection film according to the present invention will be described below in detail with reference to the drawings. In addition, this invention is not limited by the following embodiment.
First, the operation and effect of the present invention will be described.

In the antireflection film of the present invention, the SiO ₂ has a lower refractive index Following MgF ₂ in the porous structure, and the porous SiO ₂ layer was adjusted to a refractive index substantially equal to that of MgF _2, and the film thickness 50nm following MgF ₂ layers , Is used. The MgF ₂ layer is formed so as to be adjacent to a surface far from the substrate of the porous SiO ₂ layer. As a result, high scratch resistance is achieved while maintaining reflectance characteristics that are practically acceptable.

By using a porous SiO ₂ layer, the same reflectance characteristics can be obtained even if the film thickness of the MgF ₂ layer is less than half that of the conventional one, so that the scratch resistance can be improved. Further, by forming MgF ₂ as an upper layer of porous SiO ₂ , water repellency as an antireflection film can be ensured, so that no clouding occurs due to moisture and reflection characteristics do not shift.

The film density of SiO ₂ can be changed by adjusting the pressure during film formation. Specifically, by increasing the film forming pressure, the film density of SiO ₂ can be lowered, and thereby a porous SiO ₂ having a refractive index of 1.34 to 1.44 can be produced. .

MgF ₂ can be formed by sputtering using granular MgF ₂ as a film raw material. More specifically, while maintaining the temperature of the MgF ₂ surface as a target between 650 ° C. and 1100 ° C. and performing sputtering while introducing a gas containing at least one of oxygen and nitrogen, at least one of MgF ₂ is obtained. The part is jumped out in a molecular state, and a film is formed with MgF ₂ in this molecular state.

Examples will be described below. First, Example 1 and Comparative Examples 1 to 3 as a multilayer antireflection film will be described.
Example 1
FIG. 1 is a cross-sectional view illustrating a layer structure of a multilayer antireflection film according to the first embodiment. As shown in FIG. 1, the multilayer antireflection film of Example 1 has a layer structure in which an intermediate layer 20 and a final layer 30 are laminated in this order on a substrate 10.
As the substrate 10, S-LAH58 (manufactured by OHARA) is used.
The intermediate layer 20 is laminated in the order of the SiO ₂ layer 21, the Nb ₂ O ₅ layer 22, the SiO ₂ layer 23, and the Nb ₂ O ₅ layer 24 from the substrate side. The intermediate SiO ₂ layers 21 and 23 are formed by, for example, a method of performing reactive sputtering in a mixed gas of Ar and O ₂ using a Si target, or plasma oxidizing a Si film formed by sputtering using a Si target. It is formed by a method, a method of forming an oxide film by high-frequency sputtering of a SiO ₂ target, a method of forming a film of SiO ₂ by a vacuum evaporation method, or a method of forming a film on a heated substrate by decomposition of a reactive gas. .
The Nb ₂ O ₅ layers 22 and 24 may be formed by, for example, a method of performing reactive sputtering in a mixed gas of Ar and O ₂ using an Nb target, or plasma oxidizing an Nb film formed by sputtering using an Nb target. And a method of forming an oxide film by high-frequency sputtering of a Nb ₂ O ₅ target, or a method of forming Nb ₂ O ₅ by a vacuum evaporation method.
The intermediate SiO ₂ layers 21 and 23 may be either porous SiO ₂ or normal SiO ₂ , and have any film thickness that provides good reflectivity characteristics as the entire antireflection film.

The final layer 30 which is the outermost layer of the multilayer antireflection film is adjacent to a porous SiO ₂ layer 31 having a refractive index of 1.34 to 1.44 at a wavelength of 500 nm and a surface far from the substrate of the porous SiO ₂ layer. And a formed MgF ₂ layer 32 having a film thickness of 5 to 50 nm.
Also, the final layer 30 includes a first step of the SiO ₂ deposited by sputtering by setting the film formation pressure to 0.5～10Pa, on the SiO ₂ was deposited in the first step, the particle size 0.1 The second step of forming a MgF ₂ film by sputtering in an O ₂ gas atmosphere using a granular MgF ₂ of 10 mm as a target.

The porous SiO ₂ layer 31 of the final layer 30 in Example 1 is a state in which the flow rate of Ar gas, the flow rate of O ₂ gas, and the exhaust rate from the chamber in which sputtering is performed are adjusted using Si as a target in the first step. Thus, reactive sputtering is performed at a film forming pressure of 10 Pa to form a SiO ₂ layer having a thickness of 75 nm.

Here, as conditions for setting the refractive index of the porous SiO ₂ layer 31 to 1.34, the flow rate of Ar gas is 40 sccm, the flow rate of O ₂ is 20 sccm, and the exhaust rate is adjusted by adjusting the degree of opening and closing of the main valve. This adjusts the film forming pressure to 10 Pa. Further, a film is formed by reactive sputtering with a DC output of 800 W. Here, “sccm” is an abbreviation for standard cc / min, and indicates a flow rate per minute at 1 atmosphere under a constant temperature.
The refractive index of the porous SiO ₂ layer 31 can be adjusted in the range of 1.34 to 1.44 by adjusting the degree of opening and closing of the main valve and setting the film forming pressure to 0.5 to 10 Pa.

Subsequently, as a second step, MgF ₂ having a particle diameter of 1 to 3 mm is used as a target on the porous SiO ₂ layer 31 formed in the first step, and O ₂ gas is introduced to form a MgF film by sputtering. _Two layers 32 are formed to a thickness of 20 nm. More specifically, after evacuating the chamber to 7 × 10 ⁻⁵ Pa, plasma is generated in a state where O ₂ gas is introduced to 4 × 10 ⁻¹ Pa, and MgF ₂ is heated by this plasma to perform sputtering. I do.
When the refractive index of the porous SiO ₂ layer 31 is 1.44, the film thickness is preferably 45 nm, and the film thickness of the MgF ₂ layer 32 formed on the SiO ₂ layer 31 is preferably 50 nm.
In this case, the thickness of the intermediate layer 30 is adjusted so that the optical characteristics (reflectance characteristics) are the best.

(Comparative Example 1)
In the antireflection film of Comparative Example 1, an MgF ₂ layer having a thickness of 55 nm is formed on the intermediate layer as the final layer, and SiO ₂ having a refractive index of 1.46 is provided on the surface far from the substrate of the MgF ₂ layer. The protective layer has a thickness of 30 nm. MgF ₂ and SiO ₂ are formed by sputtering. The substrate and the intermediate layer have the same configuration as in the first embodiment. The film thickness of the intermediate layer is adjusted so that the optical characteristics (reflectance characteristics) are the best.

(Comparative Example 2)
In the antireflection film of Comparative Example 2, only MgF ₂ having a thickness of 95 nm is formed on the intermediate layer as the final layer. MgF ₂ is formed by sputtering. The substrate and the intermediate layer have the same configuration as in the first embodiment. The film thickness of the intermediate layer is adjusted so that the optical characteristics (reflectance characteristics) are the best.

(Comparative Example 3)
In the antireflection film of Comparative Example 3, as the final layer, SiO ₂ having a refractive index of 1.46 is formed with a film thickness of 45 nm on the intermediate layer, and MgF ₂ is formed with a film thickness of 50 nm on this SiO _2. doing. Here, SiO ₂ with a refractive index of 1.46 is not porous, unlike the SiO ₂ of the final layer of Example 1. MgF ₂ and SiO ₂ are formed by sputtering. The substrate and the intermediate layer have the same configuration as in the first embodiment. The film thickness of the intermediate layer is adjusted so that the optical characteristics (reflectance characteristics) are the best.

Next, the characteristics and effects of Example 1 and Comparative Examples 1 to 3 are compared.
FIG. 2 is a graph showing optical characteristics of the antireflection films of Example 1 and Comparative Examples 1 to 3. FIG. 2 shows the reflectance as an antireflection film in the visible region, where the horizontal axis represents the wavelength of irradiation light (unit: nm) and the vertical axis represents the reflectance (unit:%).
As shown in FIG. 2, the multilayer antireflection film of Example 1 obtained high optical characteristics equivalent to those of Comparative Example 2 in which the final layer was made of only the MgF ₂ layer. This is because the refractive index can be adjusted in the range of 1.34 to 1.44 by making the SiO ₂ porous, so that the MgF ₂ has a thin film thickness of 50 nm or less with high scratch resistance. Even so, it is shown that high optical characteristics similar to those of the antireflection film of Comparative Example 2 can be obtained.

  On the other hand, the antireflection films of Comparative Example 1 and Comparative Example 3 show undesirable optical characteristics compared to the antireflection films of Example 1 and Comparative Example 2 (FIG. 2). Specifically, in the wavelength range of about 430 nm to 650 nm, the antireflection films of Comparative Example 1 and Comparative Example 3 have a higher reflectance than the antireflection films of Example 1 and Comparative Example 2.

FIG. 3 is a table comparing the characteristics of the antireflection films of Example 1 and Comparative Examples 1 to 3.
(1) “Cloudy” is the result of evaluating the occurrence of cloudy after the environmental resistance test.
The environmental resistance test is a test in which a target antireflection film is placed every 24 hours for a total of 7 days in an environment of a temperature of 70 degrees and a humidity of 40% and an environment of a temperature of 40 degrees and a humidity of 90%.
“Cloudy” is evaluated with ○ indicating that the change in transmittance before and after the environmental test is less than 0.3% at each wavelength of 450 nm to 650 nm, and x indicating 0.3% or more.

  (2) “Characteristic shift” was evaluated with a reflectance change amount of less than 0.1% before and after the environmental test described above as ○, and 0.1% or more as × at each wavelength of 450 nm to 650 nm. ing.

(3) “Scratch resistance” is evaluated by a method in which # 0000 steel wool is rubbed 100 times with a load of 500 gf / cm ^2. When there is, it is set as x.

  As shown in FIG. 3, Comparative Example 1 has a cloudiness and characteristic shift with “x”, and Comparative Example 2 has a scratch resistance with “x”, whereas Example 1 and Comparative Example 3 have a cloudiness. Both the characteristic shift and the scratch resistance are evaluated as “Good”.

According to FIG.2 and FIG.3, in Example 1 and Comparative Examples 1-3, it is a level which does not have a practical problem in all of cloudiness, a characteristic shift, and scratch resistance, exhibiting a high optical characteristic. This is only Example 1. In addition, this result shows that the final layer is formed so as to be adjacent to a porous SiO ₂ layer having a refractive index of 1.34 to 1.44 at a wavelength of 500 nm and a surface far from the substrate of the porous SiO ₂ layer. The same applies to the case of being composed of a MgF ₂ layer having a thickness of 5 to 50 nm.

Next, Example 2 and Comparative Examples 4 to 6 as single-layer antireflection films will be described.
(Example 2)
The single-layer antireflection film of Example 2 has a layer structure in which a final layer is formed on a substrate.
The same S-LAH58 (manufactured by OHARA) as in Example 1 is used as the substrate.

The final layer which is the outermost layer of the single-layer antireflection film is formed so as to be adjacent to a porous SiO ₂ layer having a refractive index of 1.34 to 1.44 at a wavelength of 500 nm and a surface far from the substrate of the porous SiO ₂ layer. And a MgF ₂ layer having a film thickness of 5 to 50 nm.
Also, the final layer, a first step of the SiO ₂ deposited by sputtering by setting the film formation pressure to 0.5～10Pa, on the SiO ₂ was deposited in the first step, the particle size 0.1 The second step of forming a MgF ₂ film by sputtering in an O ₂ gas atmosphere using 10 mm granular MgF ₂ as a target.

The porous SiO ₂ layer as the final layer in Example 2 was prepared by adjusting the flow rate of Ar gas, the flow rate of O ₂ gas, and the exhaust rate from the chamber in which sputtering is performed using Si as a target in the first step. Reactive sputtering is performed at a film forming pressure of 10 Pa to form a SiO ₂ layer having a thickness of 80 nm. Here, the conditions for setting the refractive index of the porous SiO ₂ layer to 1.34 are the same as those in the first embodiment. Further, the refractive index of the porous SiO ₂ layer can be adjusted in the range of 1.34 to 1.44 by adjusting the degree of opening and closing of the main valve and setting the film forming pressure to 0.5 to 10 Pa.

Subsequently, as in Example 1, as a second step, sputtering is performed by introducing O ₂ gas onto a porous SiO ₂ film formed in the first step, targeting granular MgF ₂ having a particle diameter of 1 to 3 mm as a target. An MgF ₂ layer is formed to a thickness of 20 nm by film formation.
When the refractive index of the porous SiO ₂ layer is 1.44, the film thickness is preferably 50 nm, and the MgF ₂ layer formed on the SiO ₂ layer is preferably 50 nm.

(Comparative Example 4)
In the antireflection film of Comparative Example 4, an MgF ₂ layer having a film thickness of 60 nm is formed on the substrate as the final layer, and SiO ₂ having a refractive index of 1.46 is surface-protected on the surface of the MgF ₂ layer far from the substrate. A layer of 30 nm is formed. MgF ₂ and SiO ₂ are formed by sputtering. The substrate has the same configuration as in the second embodiment.

(Comparative Example 5)
In the antireflection film of Comparative Example 5, only MgF ₂ having a film thickness of 101 nm is formed on the substrate as the final layer. MgF ₂ is formed by sputtering. The substrate has the same configuration as in the second embodiment.

(Comparative Example 6)
In the antireflection film of Comparative Example 6, as a final layer, the SiO ₂ having a refractive index of 1.46 was formed with a thickness of 50nm on the substrate, the MgF ₂ was deposited thereon to a thickness of 50nm on the SiO ₂ ing. Here, SiO ₂ with a refractive index of 1.46 is not porous, unlike the SiO ₂ of the final layer of Example 2. MgF ₂ and SiO ₂ are formed by sputtering. The substrate has the same configuration as in the second embodiment.

Next, the characteristics and effects of Example 2 and Comparative Examples 4 to 6 are compared.
FIG. 4 is a graph showing optical characteristics of the antireflection films of Example 2 and Comparative Examples 4 to 6. FIG. 4 shows the reflectance as an antireflection film in the visible region, as in FIG. 2, where the horizontal axis represents the wavelength of irradiation light (unit: nm) and the vertical axis represents the reflectance (unit:%).
As shown in FIG. 4, the multilayer antireflection film of Example 2 obtained high optical characteristics equivalent to those of Comparative Example 5 in which the final layer was made of only the MgF ₂ layer. This is because the refractive index can be adjusted in the range of 1.34 to 1.44 by making the SiO ₂ porous, so that the MgF ₂ has a thin film thickness of 50 nm or less with high scratch resistance. Even so, it is shown that high optical characteristics similar to those of the antireflection film of Comparative Example 5 can be obtained.

  On the other hand, the antireflection films of Comparative Example 4 and Comparative Example 6 show undesirable optical characteristics compared to the antireflection films of Example 2 and Comparative Example 5 (FIG. 4). Specifically, in the wavelength range of about 430 nm to 650 nm, the antireflection films of Comparative Example 4 and Comparative Example 6 have a higher reflectance than the antireflection films of Example 2 and Comparative Example 5.

FIG. 5 is a table comparing the characteristics of the antireflection films of Example 2 and Comparative Examples 4 to 6.
For Example 2 and Comparative Examples 4 to 6, as in Example 1 and Comparative Examples 1 to 3, “cloudiness”, “characteristic shift”, and “scratch resistance” were evaluated.
As shown in FIG. 5, Comparative Example 4 was evaluated with a cloudiness and a characteristic shift of “x” as in Comparative Example 1, and Comparative Example 5 was scratched with a rating of “x” as in Comparative Example 2. . As for Example 2 and Comparative Example 6, as in Example 1 and Comparative Example 3, all of cloudiness, characteristic shift, and scratch resistance are evaluated as “Good”.

According to FIG. 4 and FIG. 5, among Example 2 and Comparative Examples 4 to 6, while exhibiting high optical characteristics, there is no practical problem in any of cloudiness, characteristic shift, and scratch resistance. This is only Example 2. As a result, the final layer was formed so as to be adjacent to a porous SiO ₂ layer having a refractive index of 1.34 to 1.44 at a wavelength of 500 nm and a surface far from the substrate of the porous SiO ₂ layer. The same applies to the case of being composed of a MgF ₂ layer of ˜50 nm.

  As described above, the antireflection film and the method for forming the antireflection film according to the present invention are useful for realizing high scratch resistance while maintaining reflectance characteristics.

Claims (2)

A porous SiO ₂ layer having a refractive index of 1.34 to 1.44 at a wavelength of 500 nm;
An MgF ₂ layer having a film thickness of 5 to 50 nm formed so as to be adjacent to a surface far from the substrate of the porous SiO ₂ layer;
An antireflective film characterized by comprising: A first step in which the film forming pressure is set to 0.5 to 10 Pa and SiO _{2 is formed} by sputtering;
A second step of sputtering MgF ₂ in an O ₂ gas atmosphere using a granular MgF ₂ having a particle size of 0.1 to 10 mm as a target on the SiO ₂ formed in the first step;
A method for forming an antireflection film, comprising:

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