JP6383976B2 - Antireflection structure and manufacturing method thereof - Google Patents

Description

  The present invention relates to an antireflection structure and a method for manufacturing the same.

  In recent years, in display devices such as mobile phones, personal digital assistants (PDAs), tablet PCs, and flat-screen televisions such as liquid crystal televisions, cover glasses (protective glasses) have been used to protect the display and improve aesthetics. Is increasing. A cover glass of a thin TV such as a liquid crystal TV may be subjected to processing such as antireflection on the surface. In addition, in an optical lens used in an optical device such as a camera, antireflection processing is often performed on the surface of the optical lens in order to improve transmittance and suppress flare and ghost caused by stray light.

  As an antireflection structure on the surface of a glass substrate, a fine concavo-convex structure (hereinafter also referred to as a fine structure), which is also called a moth-eye structure, is known. In a structure having such an antireflection structure, a fine structure having an appropriate period and height is formed, and high antireflection performance is exhibited in a wide wavelength region and an incident angle without scattering of light. As the shape of the convex portion, a cone shape whose volume gradually increases from the incident medium (for example, air) side toward the glass substrate side is preferable. Further, in order to suppress light scattering and obtain sufficient antireflection performance, a fine structure having a height of 250 nm or more and a period of visible light wavelength (380 nm to 780 nm) or less is required.

  As a method of forming a fine structure on the surface of a glass substrate, a method of dry-etching the glass substrate using metal fine particles such as gold and silver as a mask has been proposed (see, for example, Patent Document 1 and Non-Patent Document 1). . In this method, it is possible to form a fine structure without using a complicated lithography technique.

  However, in the methods disclosed in Patent Document 1 and Non-Patent Document 1, it is difficult to form a fine structure having a cone shape and a sufficient height and a uniform height and period.

Special table 2013-515970 gazette

G. C. Park et.al., APPLIED OPTICS Vol.51 (2012) 5890

  In the process of considering the cause, the inventors of the present invention, when using a dry etching technique using a silver fine particle layer as a mask, depending on the composition of the glass constituting the glass substrate, the shape and height of the resulting microstructure And found that the uniformity is different. And as a result of considering the cause of the difference in the shape of such a fine structure, the following knowledge was obtained. In the present specification, “glass substrate containing A” means a substrate made of glass containing A in the composition.

  That is, in a glass substrate containing an alkali metal oxide, the glass in the vicinity of the surface of the glass substrate (hereinafter referred to as a surface layer or a surface layer portion) is applied by an electric field applied in a dry etching process when forming a fine structure on the surface. The silver fine particles formed as a mask move to the surface glass of the glass substrate and diffuse so that the alkali metal moves inside and exchanges with the moved alkali metal. Thus, the silver ions diffused into the glass on the surface layer of the glass substrate can function as a mask for dry etching even if silver fine particles deposited on the glass substrate disappear by dry etching. A fine structure having is obtained.

  On the other hand, in the glass substrate that does not contain an alkali metal such as quartz glass used in the method disclosed in Patent Document 1, there is no movement of the alkali metal in the glass substrate in the dry etching step, and the silver ion Since diffusion into the glass substrate hardly occurs, only the silver fine particle layer deposited on the surface of the glass substrate functions as a mask. Therefore, the glass substrate can be dry etched only for the time until the silver fine particle layer disappears, and a sufficiently high fine structure cannot be formed.

  In the borosilicate glass or soda lime glass used in the method disclosed in Non-Patent Document 1, silver fine particles become silver ions and diffuse into the glass substrate in the dry etching process. Therefore, the height and period of the fine structure are not uniform. As a result, there is a problem that incident light is scattered in the fine structure portion and this portion looks white.

  The present invention has been made to solve such a problem, and an object thereof is to provide an antireflection structure having high antireflection performance in which light scattering is suppressed, and a method for manufacturing the same.

  As a result of intensive studies based on the above findings, the present inventors have found that a glass substrate having a composition with a relatively high alkali metal content and capable of achieving a high exchange rate for alkali metal ions and silver ions is obtained. The present inventors have found that the above problem can be solved because silver ions can be uniformly diffused in a glass substrate, and the present invention has been completed.

Each of the antireflection structures of the present invention is an antireflection structure having a base portion made of glass and a fine structure portion, and the base portion has the fine structure portion on the surface, and the fine structure portion is , Having a fine concavo-convex structure with a period of less than or equal to the wavelength of visible light, the glass in the base portion containing a total of 15% or more of alkali metal oxides in terms of oxide-based mass percentage, and Al ₂ O ₃ Ri silicate glass der containing more than 7%, the glass in the microstructure portion contains silver, said glass in the microstructure portion of the content of silver to the total of alkali metal and silver content The ratio is 3 mol% or more and 6 mol% or less .

In the antireflection structure of the present invention, the ratio of the total content of alkali metal oxides to the content of Al ₂ O _{3 in} the oxide-based mass percentage display in the glass in the base portion is 1.0 to 1.9 is preferred. Further, the alkali metal oxide is preferably a Na ₂ O and _{K 2} O.
And the glass in the base portion is a mass percentage display based on oxide,
Al ₂ O ₃ from 7% to 20%,
Na ₂ O 0-25%,
K ₂ O 0 to 25%
The SiO ₂ 45% ~68%,
0-10% of CaO,
And other oxides containing 0-33%, it is not preferable to contain 15% to 25% in total of Na ₂ O and _{K 2} O.

  The display device of the present invention includes the antireflection structure of the present invention described above. The optical apparatus of the present invention is characterized by having an optical lens having the antireflection structure of the present invention described above on its surface.

The method for producing an antireflective structure of the present invention is a method for producing the antireflective structure of the present invention, containing a total of 15% or more of alkali metal oxides in terms of oxide-based mass percentage, and A silver film is formed on the surface of a glass substrate made of silicate glass containing 7% or more of Al ₂ O _3, and the silver film is heat-treated to form a silver pattern having a shape in which a large number of minute islands are scattered. The method includes a step of forming, a step of dry etching the glass substrate using the silver pattern as a mask, and a step of removing the silver pattern.

  According to the present invention, an antireflection structure having high antireflection performance with reduced light scattering can be obtained.

It is sectional drawing which shows an example of the manufacturing method of the reflection preventing structure of this invention. 2 is a SEM photograph of a silver pattern in Example 1. 4 is a SEM photograph of a cross section of the antireflection structure obtained in Example 1. 6 is a SEM photograph of a cross section of the antireflection structure obtained in Example 4. 6 is a SEM photograph of a cross section of the antireflection structure obtained in Example 5. 6 is a SEM photograph of a cross section of the antireflection structure obtained in Example 6.

Embodiments of the present invention will be described below.
The antireflection structure of the present invention has a fine concavo-convex structure (microstructure) having a period equal to or less than the wavelength of visible light on the surface of a glass substrate. The glass substrate used in the present invention is made of silicate glass containing a total of 15% or more of alkali metal oxides and 7% or more of Al ₂ O ₃ in terms of mass percentage based on oxide.
First, the composition of the silicate glass constituting the glass substrate will be described. In the following glass compositions, “%” represents “mass%” unless otherwise specified.

<Glass composition>
In the formation of a fine structure on the surface of a glass substrate using a dry etching technique using silver fine particles as a mask, the present inventors include a total of 15% or more of alkali metal oxides and 7% of Al ₂ O ₃ . It has been found that by using a silicate glass substrate containing at least%, it is possible to form a highly uniform microstructure having a sufficient height and good shape. As the alkali metal oxides, for _{example, Li 2 O, Na 2 O} , K 2 O, Cs 2 O may be mentioned, Na ₂ O and _{K 2} O Among these are preferred.

The total content of alkali metal oxides may be 17% or more, or 19% or more. Further, the total content of alkali metal oxides may be 25% or less, 23% or less, or 20% or less.
The content of Al ₂ O ₃ may be 9% or more, or 11% or more. Further, it may be 20% or less, 16% or less, or 13% or less.

  In a glass substrate made of silicate glass having the above composition, silver constituting a silver layer (for example, a silver pattern) formed as a mask on the glass substrate is ionized by an electric field applied during dry etching, and the glass substrate Move in and spread. In addition to the silver layer formed on the glass substrate, the silver ion diffusion region formed in the glass substrate functions as a mask for dry etching. Therefore, the dry etching mask functions effectively for a long time, and each protrusion has a cone shape and a sufficient height, and a uniform fine structure is formed with a period of less than the wavelength range of visible light. . The height, shape, and period of the fine structure will be described in more detail later.

As the alkali metal oxide, R ₂ O (wherein R is at least one selected from the group consisting of Li, Na, K, and Cs. Preferably, at least one selected from Na and K) is contained. The diffusion of silver ions and the formation of a fine structure in the glass composition will be further described. Due to the electric field during dry etching, alkali metal ions (hereinafter also referred to as R ions, where R is the same as the description of R in R ₂ O) move and diffuse inside the substrate. With the diffusion, the silver constituting the silver layer on the glass substrate is ionized to form monovalent silver (Ag) ions (hereinafter also referred to as silver ions) and penetrates and diffuses into the surface layer of the glass substrate. Thus, since a diffusion region of silver ions having a lower etching rate can be formed in the glass substrate as compared with a region of the glass substrate where silver ions are not diffused, a favorable fine structure is realized.
As the R ions move on the surface of the glass substrate, the ionized silver penetrates and diffuses into the glass substrate because the valence of the R ions is equal to that of the silver ions, the ionic radius of the R ions, and the silver ions. This is because the ion radius is close. That is, when R ions on the surface layer of the glass substrate move inside, silver ions penetrate into the glass substrate and diffuse so as to exchange with these ions.

  The ease of diffusion of silver ions into the glass substrate varies depending on the content of R ions in the glass substrate and the rate at which silver ions exchange with R ions in the glass (hereinafter referred to as ion exchange rate). In the present application, the movement of R ions (alkali metal ions) and the entry of silver ions into the sites occupied by the R ions is expressed as “exchange” or “ion exchange”.

Since the glass substrate used as a starting material in the production of the antireflection structure of the present invention has a glass composition containing a total of 15% or more of alkali metal oxides and 7% or more of Al ₂ O ₃ , The ion exchange rate is high, and silver ions can be diffused to a deep region inside the glass substrate. Next, the operation of the _Al 2 _{O 3} which is contained in the glass substrate.

In the case of a silicate glass containing alkali metal ions, non-crosslinked oxygen is generated to retain the alkali metal ions. Since non-crosslinked oxygen has a high negative charge density, it strongly attracts alkali metal ions. When Al is contained in the silicate glass, non-bridging oxygen can be reduced. That is, Al has four coordinations in the glass substrate and is bonded to four oxygens. As a result, a region including four bridging oxygens centered on Al has a negative charge and can hold alkali metal ions. Further, the negative charge density in the region including the four bridging oxygens centering on Al is lower than the negative charge density of the non-bridging oxygens. Accordingly, the alkali metal ions are weakly attracted to the periphery of Al, and can easily move. Therefore, by setting the content of Al ₂ O ₃ in the glass substrate to 7% or more and reducing the amount of non-bridging oxygen strongly attracted with alkali metal ions, silver ions and alkali metal ions in the glass substrate are reduced. The ion exchange rate can be increased.

If the content of Al ₂ O ₃ in the glass substrate becomes too high, Al becomes 6-coordinated, so that the amount of non-bridging oxygen increases. The amount of non-crosslinked oxygen in the glass substrate is also correlated with the content of alkali metal ions, and is the sum of the content of alkali metal oxides with respect to the content of Al ₂ O ₃ in terms of oxide-based mass percentage. When the ratio (hereinafter referred to as R ₂ O / Al ₂ O ₃ ) is in the range of 1.0 to 1.9, the amount of non-bridging oxygen is minimized, and at this time, the above-described ion exchange rate is maximized. _{Incidentally, R 2} O in the R 2 _O / _Al 2 O ₃ indicates the total content of alkali metal oxides. For example, when R is Na and K, R ₂ O = Na ₂ O + K ₂ O.

That is, in the composition of the glass substrate used in the present invention, R ₂ O / Al ₂ O ₃ is preferably 1.0 to 1.9. R ₂ O / Al ₂ O ₃ is more preferably 1.0 to 1.85, and further preferably 1.3 to 1.85. In the glass composition, if R ₂ O / Al ₂ O ₃ is in the range of 1.0 to 1.9, the ion exchange rate at which silver ions exchange with alkali metal ions can be made sufficiently high, Silver ions can be diffused into deep regions inside the glass substrate. Also, by ionizing and diffusing most of the silver constituting the silver layer formed on the glass substrate into the glass substrate, a three-dimensional distribution of silver diffusion regions can be formed inside the glass substrate. . By using the three-dimensional silver diffusion region as a mask, a fine structure having a satisfactory shape and sufficient height and excellent as an antireflection structure can be obtained.

When the glass constituting the glass substrate used as the starting material is not a silicate glass containing a total of 15% or more of alkali metal oxides and 7% or more of Al ₂ O ₃ , silver ions are contained in the glass substrate. Therefore, the desired fine structure having excellent antireflection properties cannot be obtained.

For example, a general soda lime glass substrate has a low Al ₂ O ₃ content of less than 7%, and thus has a low ion exchange rate. Therefore, reflecting the microscopic distribution of alkali metal ions in the glass substrate, local diffusion of silver ions occurs, resulting in non-uniform diffusion of silver ions into the glass substrate, resulting in a microstructured shape. Disturbance occurs, and the uniformity of the shape tends to decrease.
In order to obtain sufficient antireflection performance, the height of the fine structure needs to be 250 nm or more. However, when a soda lime glass substrate is used, the higher the fine structure, the more the shape is disturbed. Since it becomes prominent, light scattering occurs and it looks whitish.

  Moreover, since the total content of alkali metal oxides is less than 15% in a general borosilicate glass substrate, the amount of silver ions that can diffuse into the glass substrate is small. Therefore, it is difficult to form a fine structure having a desired cone shape, and high antireflection performance cannot be obtained. The reason for this is considered that the diffusion region of silver ions is limited to a region shallow from the surface. Since the borosilicate glass substrate has a small diffusion amount of silver ions, the silver ions serving as a mask for dry etching remain in a shallow region on the surface and do not diffuse so much in the depth direction. As a result, it is considered that the shape obtained by dry etching is not a conical shape, but tends to be a columnar shape whose cross-sectional area does not change much in the depth direction.

  Furthermore, in the alkali-free glass substrate conventionally used for the liquid crystal panel, since the alkali metal oxide is not substantially contained in the glass substrate, silver ions do not enter and diffuse into the glass substrate. . And since the etching rate of an alkali free glass substrate is low compared with silver, the silver pattern which is a mask is etched faster than a glass substrate, and formation of a fine structure itself is difficult. Further, even in a quartz glass substrate having a higher etching rate than that of a non-alkali glass substrate, since the alkali metal oxide is not substantially contained in the glass substrate, silver ions do not diffuse into the glass substrate. Therefore, it is difficult to form a sufficiently high microstructure.

On the other hand, the glass substrate used in the present invention is composed of a silicate glass containing a total of 15% or more of alkali metal oxides and containing 7% or more of Al ₂ O _3. It has a good shape and can form a uniform fine structure.

It is preferable that the silicate glass which comprises the glass substrate used for this invention has the following compositions, for example.
That is, with oxide-based mass percentage display,
Al ₂ O ₃ 7% to 20%
Na ₂ O 0-25%,
K ₂ O 0 to 25%
The SiO ₂ 45% ~68%,
0-10% of CaO,
And 0 to 33% of other oxides, and a total of 15 to 25% of Na ₂ O and K ₂ O is preferable.
The total content of Na ₂ O and K ₂ O is preferably 17% to 23%, more preferably 19% to 21%. Further, the Al ₂ O ₃ content is preferably 9% to 16%, more preferably 11% to 13%.

SiO ₂ is a component that forms a glass skeleton. If it is less than 45%, the heat resistance and chemical durability of the glass substrate may be lowered. Moreover, there exists a possibility that it cannot etch easily with the fluorine-containing compound used as etching gas at the time of forming a fine structure. More preferably, it is 50% or more, More preferably, it is 55% or more. However, if it exceeds 68%, the high-temperature viscosity of the glass is increased, and there is a possibility that a problem that the solubility is deteriorated may occur. More preferably, it is 65% or less, More preferably, it is 62% or less.

  CaO reacts with a fluorine-containing compound used as an etching gas to form calcium fluoride. Calcium fluoride has higher binding energy than other elemental fluorides contained in glass, and is difficult to etch. Since the side etching of the fine structure is suppressed by the formation of calcium fluoride, CaO may be contained in order to form a cone shape. The content is more preferably 2% or more, and further preferably 3% or more. However, if it exceeds 10%, the devitrification temperature of the glass may increase. More preferably, it is 9% or less, More preferably, it is 8% or less.

The silicate glass which comprises the glass substrate used for this invention may contain another component in the range which is not contrary to the objective of this invention. For example, you may contain 0 to 33% of other oxides. Specifically, one or more of the following oxides may be contained, for example, B ₂ O ₂ is 0 to 1%, MgO is 0 to 10%, SrO is 0 to 19%, and BaO is 0 to 12%. , ZrO ₂ may be contained in an amount of 0 to 11%. By containing these components in the above range, solubility, devitrification, and the like during production of the glass substrate can be improved.

<Method for producing antireflection structure>
The method for producing an antireflection structure according to the present invention is a method for producing an antireflection structure having a fine concavo-convex structure having a period of less than or equal to the wavelength of visible light on the surface of a glass substrate. Then, a silver film is formed on the surface of a glass substrate made of a silicate glass containing a total of 15% or more of alkali metal oxides and containing 7% or more of Al ₂ O ₃ , and heat-treating the silver film, A step of forming a silver pattern having a shape in which a large number of minute islands are scattered, a step of dry-etching the glass substrate using the silver pattern as a mask, and a step of removing the silver pattern, To do. That is, in the manufacturing method of the present invention, a silver pattern is formed on the surface of a glass substrate, dry etching is performed, the silver pattern is removed, and an antireflection structure is obtained.
Below, the manufacturing method of the reflection preventing structure of this invention is demonstrated based on drawing.
In the manufacturing method of the present invention, first, as shown in FIG. 1A, a glass substrate 1 is prepared, and a silver film 2 is formed on the glass substrate 1. The composition of the glass substrate 1 is as described in the item of the glass composition. Although the thickness of the glass substrate 1 is not specifically limited, For example, what is necessary is just 0.05 mm-10 mm, and 0.5 mm-6 mm are preferable.

  Although the formation method of the silver film 2 is not specifically limited, For example, a dry coating method is used. Examples of the dry coating method include a PVD method (Physical Vapor Deposition) and a CVD method (Chemical Vapor Deposition). The PVD method is preferable, and among the PVD methods, the vacuum deposition method, the sputtering method, and the ion plating method are preferable. Further, among these, the sputtering method is particularly preferable because it is excellent in controllability of a thin film of several tens of nm and has high versatility.

The film thickness of the silver film 2 is preferably 20 nm or less, and more preferably 15 nm or less so that a silver pattern having a desired shape that will serve as a dry etching mask in a subsequent step can be obtained.
That is, in order to form a fine structure having a period equal to or less than the wavelength of visible light by dry etching on the surface of a glass substrate, a silver pattern that serves as a mask has a number of minute islands (hereinafter referred to as minute islands). Without being connected to each other, it is necessary to form in a shape interspersed at a pitch of 50 nm to 400 nm, preferably 100 nm to 300 nm. The pattern shape of the silver pattern and the period (pitch) in which the micro islands are scattered can be controlled by the film thickness of the silver film 2. If the film thickness of the silver film 2 is 20 nm or less, the micro islands are It is possible to form a silver pattern having a desired shape scattered in a cycle. Moreover, the film thickness of the silver film 2 should just be 2 nm or more in order to form the silver pattern of the thickness which functions as a mask, and 4 nm or more is preferable.

  Next, the glass substrate 1 on which the silver film 2 is formed is heat-treated, and as shown in FIG. 1B, a shape in which a large number of small islands 3a serving as a mask for dry etching are scattered at a predetermined cycle is formed. A silver pattern 3 is formed.

The heat treatment may be performed under the condition that the silver pattern 3 having the above shape is formed from the silver film 2. Since silver has poor wettability with glass, it flows even at a temperature below the melting point of silver, and a pattern having a shape in which fine islands 3a are scattered is formed. The heat treatment temperature is preferably 100 ° C. or higher, and more preferably 150 ° C. or higher. The heat treatment temperature is preferably 500 ° C. or lower which is lower than the softening point of the glass substrate 1. The heat treatment time is preferably 5 minutes or longer, and more preferably 10 minutes or longer. From the viewpoint of productivity, the heat treatment time is preferably within 1 hour. The heat treatment atmosphere is not particularly limited, and can be, for example, the air, a nitrogen atmosphere, a vacuum atmosphere, or the like.
The heat treatment may be performed simultaneously with the formation of the silver film 2. For example, the silver film 2 can be formed by sputtering while heating the glass substrate 1 by sputtering, whereby the silver film 2 and the silver pattern 3 can be formed simultaneously by heat treatment.

  Thus, after forming the silver pattern 3 on the surface of the glass substrate 1, as shown in FIG.1 (c), the glass substrate 1 is dry-etched by using the silver pattern 3 as a mask, and the fine structure 4 is formed in the surface. .

  The dry etching can be performed by ICP (Inductively Coupled Plasma) type reactive ion etching. Other discharge type plasma etching apparatuses such as a CCP (Capacitive Coupled Plasma) type and an ECR (Electron Cyclotron Resonance) type may be used. For etching the glass substrate 1 having a low etching rate, ICP capable of generating high-density plasma is preferable.

The power of the RF (high frequency) power source for generating ICP plasma may be 10 W to 2 kW, and preferably 50 W to 500 W. The power of the bias RF power supply on the substrate side may be 10 W to 1 kW, and preferably 50 W to 500 W.
As an etching gas, a gas that can secure an etching selectivity between the silver pattern 3 and the glass substrate 1 may be used. For example, fluorine-containing compounds such as fluorocarbons can be used. Specifically, CF ₄ , CHF ₃ , SF ₆ or the like can be given. Further, a diluent gas such as He may be mixed with the etching gas. The pressure in the chamber of the etching gas or diluted etching gas is preferably 0.1 Pa to 10 Pa. The etching time can be determined by the etching depth. In order to manufacture the antireflection structure, a time during which the glass substrate 1 is etched to a depth of 250 nm to 500 nm is preferable.

Next, as shown in FIG.1 (d), the silver which remained on the surface of the glass substrate 1 is removed, and the antireflection structure 5 in which the fine structure 4 was formed in the surface is obtained.
The method for removing silver is not particularly limited as long as the silver on the surface of the glass substrate 1 can be removed without affecting the fine structure 4. For example, silver can be removed by dipping in an aqueous nitric acid solution. The concentration of nitric acid is preferably in the range of 1% by mass to 70% by mass, and preferably 5% by mass to 20% by mass. The immersion time may be a time until the silver on the surface of the glass substrate 1 can be removed, and is preferably 1 minute to 20 minutes.
Thus, on the surface of the glass substrate 1, each anti-reflection structure has a cone shape and a sufficient height, and has a highly uniform microstructure 4 having a period equal to or less than the wavelength region of visible light. 5 can be obtained. In FIGS. 1C and 1D, reference numeral 4a indicates a silver ion diffusion region.

<Antireflection structure>
Each of the antireflection structures of the present invention has a fine structure portion and a base portion made of glass. The base portion has the fine structure portion on the surface. The fine structure portion has a fine concavo-convex structure (fine structure) having a period equal to or shorter than the wavelength of visible light.
In the following description, a fine structure portion formed on the surface of a glass substrate is referred to as a fine structure portion. Further, a portion where the fine structure of the glass substrate is not formed is referred to as a base portion.

(Base part)
The glass in the base portion of the antireflection structure has the composition described in the item of the glass composition. This composition is substantially the same as the glass composition of the glass substrate used as a starting material in the above-described production method. Before and after forming the fine structure on the surface of the glass substrate, the glass composition in the vicinity of the surface of the glass substrate varies, but in the base portion of the antireflection structure, a portion sufficiently separated from the surface of the glass substrate (for example, 10 μm or more) The glass composition of is the same as that of the glass substrate used as the starting material.

(Fine structure part)
In the fine structure portion, the shape of the convex portion is preferably a cone shape in which the diameter or area of the cross section decreases toward the tip.
Moreover, in the fine structure portion, the period that is the distance between the apexes of adjacent convex portions is not particularly limited as long as it is equal to or less than the wavelength of visible light, but is preferably 50 nm to 400 nm, and more preferably 100 nm to 300 nm.
The height of the fine structure is preferably 250 nm or more, more preferably 270 nm or more, and further preferably 290 nm or more. Here, the height of the fine structure means the height from the bottom of the concave portion at the apex of the convex portion. The height of the microstructure can be measured, for example, as the length of the shortest line between the line connecting the vertices of the convex part and the line connecting the bottom point of the concave part in a cross-sectional photograph of the microstructure by an electron microscope. it can.

  Furthermore, the microstructure is preferably uniform. Here, that the fine structure is uniform means that the period of the fine structure is not more than the visible light wavelength and the height of the fine structure is constant.

  Alkali metal ions move in the microstructure by applying an electric field during dry etching in the formation process, and instead, silver ions from the silver pattern penetrate and diffuse to form a diffusion region of silver ions. ing. That is, the glass in the fine structure portion has a composition in which the content of alkali metal ions is reduced and the content of silver ions is increased compared to the glass in the base portion.

  In the glass composition of the microstructure, the ratio of the silver content to the total of the alkali metal and silver contents (hereinafter also referred to as surface silver concentration) may be 3 mol% or more. Moreover, 6 mol or less may be sufficient. Silver that has penetrated into and diffused into the glass substrate exists as silver ions in the glass of the fine structure portion, and thus exhibits an antibacterial effect. Moreover, since most silver is ionized in a glass substrate if it is the said range, coloring will not be seen by a fine structure part. Therefore, even when the antireflection structure is used as a cover glass of a display device, there is no possibility of reducing visibility.

  As described above, since the antireflection structure of the present invention has a fine structure portion having excellent characteristics on the base portion of the glass substrate, light scattering is suppressed and high antireflection performance is achieved.

  Examples of the present invention will be specifically described below, but the present invention is not limited to these examples. In the following examples, Examples 1 to 3 are examples, and Examples 4 to 7 are comparative examples.

Examples 1-7
In each example, a fine structure was formed on the surface of a glass substrate (thickness 2 mm) having the composition shown in Table 1 by the following method.

  First, the glass substrate was cut into a rectangle having a side of 5 cm, and then a silver film was formed on one surface using a sputtering method. Film formation was performed at room temperature, and a silver film having a thickness of 10 nm was formed. Next, the glass substrate on which the silver film was formed was heated to 200 ° C. in a vacuum to form a silver pattern having a shape in which a large number of small island portions were scattered. As for the silver pattern formed in Examples 1-7, the equivalent pattern was obtained irrespective of the kind of glass substrate. An SEM photograph of this silver pattern is shown in FIG. In the formed silver pattern, the average diameter of the island part was 100 nm to 200 nm, and the period of the dot part of the island part was 100 nm to 300 nm.

Next, the glass substrate on which the silver pattern was formed was etched using an ICP plasma etching apparatus (manufactured by ULVAC, apparatus name: CE-300R). The flow rate of CF ₄ as an etching gas was 50 sccm, the flow rate of He as a dilution gas was 50 sccm, and the pressure in the chamber during etching was 1 Pa. The power of the RF power source for ICP plasma generation was 80 W, and the power of the bias RF power source on the glass substrate side was 40 W. The etching rate of the glass substrate was calculated, and the etching time was adjusted from the value so that the etching depth of the glass substrate was 300 nm.

  Next, the etched glass substrate was immersed in a 10% by mass nitric acid aqueous solution for 3 minutes to remove silver remaining on the glass substrate surface. Thus, an antireflection structure comprising a glass substrate having a fine structure formed on the surface was obtained.

Next, with respect to the antireflection structure thus obtained, the ratio of silver content to the total of the content of alkali metal and silver in the antireflection performance, the height and uniformity of the microstructure, and the alkali content in the microstructure (surface silver concentration ) Were measured and evaluated as shown below. These results are shown in Table 1 together with the glass composition of the glass substrate (content ratio of each component, (Na ₂ O + K ₂ O) and (Na ₂ O + K ₂ O) / Al ₂ O ₃ )).

<Evaluation of antireflection performance>
For the antireflection structures of Examples 1 to 7 provided with a fine structure and the glass substrate before forming the fine structure in each example, the average transmittance at a wavelength of 500 nm to 700 nm was measured with a spectrophotometer (manufactured by JASCO Corporation, (Device name: ARM-500N). Then, a value ΔT (= T ₂ −T ₁ ) obtained by subtracting the transmittance T ₁ of the glass substrate not provided with the microstructure from the transmittance T ₂ of the antireflection structure provided with the microstructure. This ΔT was used as an evaluation standard for antireflection performance.

The reason why ΔT is used as an evaluation standard for antireflection performance is as follows.
In other words, spectral reflectance can be used as an evaluation criterion for antireflection performance. However, since the reflectance decreases even when light scattering is large, the low reflectance is directly evaluated as the high antireflection performance. I can't do it. On the other hand, since ΔT decreases when light scattering is large, a larger ΔT means a structure with higher antireflection properties in which light scattering is suppressed.

<SEM image taking and measurement of the height of the fine structure>
First, in Example 1, an SEM image of the surface of the silver pattern was taken. This surface SEM image is shown in FIG. Further, the antireflection structures obtained in Examples 1 to 7 were cleaved, and a cross section was photographed using a scanning electron beam having an acceleration voltage of 1.0 kV. The cross-sectional SEM image of Example 1 is shown in FIG. 3, and the cross-sectional SEM images of Examples 4 to 6 are shown in FIGS. SEM images were taken using FE-SEM (manufactured by Hitachi High-Tech, apparatus name: SU-70), and all SEM images were taken at a magnification of 40,000 times.

  Next, the height of the fine structure was calculated from the cross-sectional SEM image thus obtained. In the cross-sectional SEM image, the length of the shortest line between a line connecting the vertices of each convex portion of the fine structure (hereinafter referred to as the vertex line) and a line connecting the bottoms of the respective concave portions (hereinafter referred to as the bottom line). This is the height of the fine structure. 3 to 6, the vertex line and the bottom line are each indicated by a broken line, and the shortest line is indicated by an arrow.

  The uniformity of the fine structure was determined based on the cross-sectional SEM image. That is, in the cross-sectional SEM image, when a concavo-convex structure with a period of 100 nm to 300 nm is formed and the height of the fine structure is constant, the uniformity is good (◯), and the period of the fine structure is in the above range. Or the case where the period and height of the fine structure are not constant, the uniformity was judged as poor (x).

<Calculation of surface silver concentration>
Using an X-ray photoelectron spectrometer (manufactured by ULVAC-PHI Co., Ltd., apparatus name: PHI5000), on the surface of the fine structure portion of the antireflection structure obtained in Examples 1 to 7, silver (Ag) and an alkali metal The molar concentration of certain Na and K was measured. The measurement was performed under the conditions of an X-ray beam diameter of 100 μm, an output of 25 W, an acceleration voltage of 15 kV, and an extraction angle of 45 °. The surface silver concentration (mol%) was calculated from the measured values of the obtained molar concentrations of Ag, Na, and K. When this measurement condition is used, the average molar concentration of Ag, Na, and K in the range of 1 nm to 2 nm from the surface of the glass substrate is measured.

From the results in Table 1 and the cross-sectional SEM images of FIGS.
As can be seen from FIG. 3, the antireflection structure of Example 1 has a period of about 100 nm to 300 nm reflecting the pitch (interval) of the fine islands of the silver pattern showing the surface SEM image in FIG. A fine structure having sufficient height and uniformity in shape is obtained. The antireflection structure of Example 1 has a large ΔT and high antireflection performance.
Also, in the antireflection structures of Examples 2 and 3, as can be seen from Table 1, a fine structure with sufficient height and good uniformity is formed, ΔT is sufficiently large, and antireflection performance is high. It has become.

Thus, alkali metal total oxide in which Na 2 _O and K _{2 O} content is at least 15 mass%, and Al ₂ O ₃ glass substrate composition content is 7 mass% or more The antireflection structures of Examples 1 to 3 manufactured using the above have high antireflection performance with high ΔT and suppressed light scattering. And in the antireflection structural body of Examples 1-3, the surface silver density | concentration in a fine structure part is 3 mol% or more and 6 mol% or less.

On the other hand, in the antireflection structures of Example 4 and Example 5 in which the fine structure was formed using the substrate made of glass having an Al ₂ O ₃ content of less than 7%, as can be seen from FIG. 4 and FIG. It can be seen that there are locally high portions and deeply dug portions in the microstructure, and the shape and period are also disturbed. Moreover, as shown in Table 1, since the height of the fine structure is high but the uniformity is poor, light scattering occurs, ΔT is small compared to Examples 1 to 3, and the antireflection performance is low. .

In addition, in the antireflection structure of Example 6 in which the fine structure was formed using the quartz glass substrate made of only SiO ₂ , as shown in FIG. 6 and Table 1, the height of the fine structure was as low as about 200 nm, and ΔT was Compared to Examples 1 to 3, the antireflection performance is small and low.

Furthermore, although the content of Al ₂ O ₃ is 7% or more, in Example 7 in which a microstructure is formed using a glass substrate having a composition not containing an alkali metal, a sufficiently high microstructure can be formed. could not. As a result of measurement by AFM (manufactured by SII Nanotechnology, apparatus name: SPA-400), the height of the fine structure was only about 20 nm, and the period was as large as about 500 nm. ΔT showed a negative value, and the antireflection performance was extremely low.

  Since the antireflection structure of the present invention has a high antireflection performance in which light scattering is suppressed, a display device such as a mobile phone, a PDA, a tablet PC, or a flat-screen television such as a liquid crystal television, and a cover for the display device It can be applied to glass and the like. Further, since it has high antireflection performance with reduced light scattering and can be applied to a curved surface, it can also be applied to the surface of an optical lens. As described above, the optical lens to which the antireflection structure of the present invention is applied can be used in an optical apparatus such as a camera or a projector.

  DESCRIPTION OF SYMBOLS 1 ... Glass substrate, 2 ... Silver film, 3a ... Micro island part, 3 ... Silver pattern, 4 ... Fine structure, 4a ... Diffusion area | region of silver ion, 5 ... Antireflection structure.

Claims (7)

Both are antireflective structures having a base portion and a fine structure portion made of glass,
The base portion has the fine structure portion on the surface,
The fine structure portion has a fine concavo-convex structure with a period equal to or shorter than the wavelength of visible light,
Glass in the base unit, as represented by mass percentage based on oxides, containing 15% or more of alkali metal oxides in total, and Ri silicate glass der containing Al ₂ O ₃ 7% or more,
The glass in the microstructure part contains silver,
The antireflection structure according to claim 1 , wherein the ratio of the silver content to the total content of alkali metal and silver in the glass in the microstructure is 3 mol% or more and 6 mol% or less . The ratio of the total content of alkali metal oxides to the content of Al ₂ O _{3 in} the oxide-based mass percentage display in the glass of the base portion is 1.0 to 1.9. The antireflection structure as described. The antireflection structure according to claim 1, wherein the alkali metal oxide is Na ₂ O and K ₂ O. The glass in the base is a mass percentage display based on oxide,
Al ₂ O ₃ from 7% to 20%,
Na ₂ O 0-25%,
K ₂ O 0 to 25%
The SiO ₂ 45% ~68%,
0-10% of CaO,
And 0 to 33% of other oxides,
Na containing 15% to 25% of the ₂ O and _{K 2} O in total, the anti-reflection structure according to any one of claims 1 to 3. The display apparatus provided with the reflection preventing structure of any one of Claims 1-4 . An optical apparatus having an optical lens having the antireflection structure according to any one of claims 1 to 4 on a surface thereof. A method for producing the antireflection structure according to any one of claims 1 to 4 ,
A silver film is formed on the surface of a glass substrate made of a silicate glass containing a total of 15% or more of alkali metal oxides and containing 7% or more of Al ₂ O ₃ in terms of oxide-based mass percentage, A step of heat-treating the silver film to form a silver pattern in which a large number of minute islands are scattered;
Dry etching the glass substrate using the silver pattern as a mask;
A method for producing an antireflection structure, comprising the step of removing the silver pattern.