KR960007881B1 - Membrane for prevention of reflection - Google Patents

Abstract

The multilayered film comprises the first layer film with medium refractive index alumina and the thickness of 0.5 O0=F0.05 O0 , the second layer film with high refractive index zirconia and titania and the thickness of 0.5 O0=F0.05 O0 , the third film with low refractive index magnesium fluoride and the thickness of 0.25 O0=F0.025 O0., where O0 is standard wavelength of visible ray.

Description

Multi-layered Anti-reflective Film of High Refractive Index Optical Components

1 is a diagram showing the configuration of a multilayer antireflection film according to the high-refractive optical component of the present invention.

2A and 2B are characteristic diagrams showing the relationship between the wavelength and reflectance of the prior art.

3 is a characteristic diagram showing the relationship between the wavelength and reflectance of the present invention shown in FIG.

* Explanation of symbols for main parts of the drawings

1: substrate 2: first layer film

3: 2nd layer film 4: 3rd layer film

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multilayer antireflection film of an optical component. In particular, even when the refractive index of a substrate is high, the three-layer thin film structure (video) increases the transmittance of a camera lens and an optical device. The present invention relates to a multilayer antireflection film that enables the thickness control of the structure to be easily controlled even by the thickness control method.

In general, the antireflection film of an optical component can be largely separated into a single layer antireflection film and a multilayer antireflection film.

For the first time, with the pursuit of high performance of optical devices, when the structure of the optical system becomes complicated and the number of lenses increases, sufficient transmittance cannot be obtained with a single layer anti-reflection film, so that the defects of the single layer anti-reflection film, that is, the low reflection wavelength region, are narrow and the residual reflectance is high. Many multilayer anti-reflective films which improve the fault which is large are used.

As described above, the multilayer anti-reflection film has superior characteristics of light transmittance than the single-layer anti-reflection film. However, the multilayer anti-reflection film has a disadvantage in that manufacturing facilities are expensive, it is difficult to accurately control the thickness of each layer, and manufacturing cost is high.

One of the basic types of the multilayer anti-reflection film is a case of a low refractive index having a refractive index (n) of about n = 1.5 of a conventional substrate. Generally, three layers of different dielectric materials are deposited. Table 1 shows.

Table 1 describes the film thickness according to the basic configuration of the conventional multilayer antireflection film, wherein the multilayer antireflection film is formed from the first layer film having the optical film thickness of? / 4 from the glass substrate side, It consists of three layers of anti-reflective films which used the 3rd layer film which is a 2-layer film (lambda) / 4.

As the dielectric material of each layer, the intermediate refractive index material of the first layer film is CeF, LaF, SiO, etc., the second layer film of ZrO, TiO, TaSO, ZnS, etc., and the third layer film of MgF, SiO, etc. are low refractive index materials. This can be used.

On the other hand, as a conventional three-layer antireflection film, for example, its constituent material is composed of CeF (λ / 4) -ZrO (λ / 2) -MgF (λ / 4), but the conventional one has a drawback of low film strength. have.

On the other hand, when AlO is used instead of CeF as the one-layer film, it is known that the film strength is increased and such defects are improved.

Since the thickness of each layer is an integer multiple of lambda / 4, the membrane structure configured to satisfy the above conditions makes it very easy to control two membranes by specifying lambda when irradiating the amount of transmittance in the visible light region.

This is because in the optical film thickness control method, the thickness of each layer becomes maximum or minimum with respect to λ.

However, in the case of depositing ZrO on an oxide such as AlO, it is accompanied by a process of heating the bottom temperature to a certain temperature for the purpose of increasing the strength, so that the refractive index gradually decreases as the thickness of ZrO increases, resulting in an uneven film in the thickness direction. Therefore, there existed a fault which the peak reflection value of the reference wavelength ((lambda)) of a 3-layer antireflection film becomes large.

As a solution to this drawback, Japanese Patent Laid-Open No. 52-31204 has a very low low refractive index interposing several layers of MgF in the middle of ZrO.

Japanese Patent Nos. 51-33750 and 51-33751 have made equivalent films equivalent to ZrO (λ / 2) homogeneous in a plurality of layers containing MgF and CeO. However, all of these conventional materials have a large difference in refractive index of the constituent material from that of ZrO (ZrO: 2.05, MgF: 1.39, CeO: W.15). If there is a slight variation in the thickness of the intervening layer and a slight difference in the interposition This also greatly affects the reflective properties of the product after deposition, which makes it difficult to obtain stable high yields.

Thereafter, a more improved type of multilayer anti-reflection film which solves the above problems is disclosed in Japanese Patent Laid-Open No. 61-51283, which shows the film thickness according to the basic structure thereof.

This structure is formed into five layers of anti-reflection films by dividing the two-layer film into three kinds of deposition materials.

Table 2 shows a slightly modified three-layer basic anti-reflective coating having a thickness of antireflection coating from the glass substrate as the first layer film (λ / 4), the second layer film (λ / 2), and the third layer film (λ / 4). As a constitution, the material of the first layer film is made of AlO, and the second layer film is made of a mixture of λ / 4 ZrO, λ / 8 ZrO and TiO, and λ / 8 so that the whole of the second layer film is 0.5λ. A laminating agent made of a ZnO material, and the material of the third layer film is made of MgF.

The above constitution is made in view of the conventional problem. Even after the deposition thickness of the intervening material layer is slightly changed by interposing a mixture layer of TiO and ZrO, which is a material having a slightly higher refractive index than ZnO, in the ZnO layer as the second layer, In other words, it is composed of a multilayer anti-reflection film which is hardly affected due to a slight variation in manufacturing conditions, in which large dispersion does not occur in the reflective properties of the product.

The mixing ratio of the mixture of ZrO and TiO is in the range of weight ratio (TiO / ZnO) = 0.07 to 0.13. When the mixing ratio is 0.07 or more and 0.13 or less, the heterogeneous effect is sufficiently obtained, but when the mixing ratio is 0.13 or more, the refractive index becomes high and the low reflection region is narrowed. In the case where the mixture contains lower oxides such as ZnO and TiO, the weight ratio is added to ZrO and TiO, respectively, so as to have a mixing ratio as described above.

On the other hand, the film thickness of the mixture was described as λ / 8, but specifically, for example, when the weight ratio of TiO / ZrO = 0.11, the thickness range should be formed within 0.09 to 0.14λ, and the peak reflectance below 0.09λ. There is no effect of lowering the surface area and the reflection area becomes narrower at 0.14 lambda or more.

2A and 2B show spectral transmittances of wavelengths and reflectances of the respective constituent films specified in Tables 1 and 2 as the prior art. The spectral transmittances for the Table 1 components are indicated by dotted lines (X, X), and Table 2 components. The spectral transmittance for is indicated by the curve (Y, Y) indicated by the solid line.

FIG. 2A shows a case where an antireflection film of a glass substrate having a refractive index n = 1.52 is deposited, and FIG. 2B shows a case where an antireflection film is deposited on a glass substrate having a refractive index n = 1.59, respectively.

As can be seen from the figure, in the case of Table 1, that is, in the case of the curve (X, X), the low reflection region is narrowed in the dot where the refractive index of the mixture material, which is the second layer, is larger than ZrO, and the curve (X, X) is TiO. The lower the mixing ratio of, the lower the refractive index but the heterogeneous improvement effect is also the opposite results.

In the deposition process, the refractive index can be changed by lowering the substrate temperature, introducing oxygen, etc., but it is not an advantageous method because it is required to reduce the deposition rate, the instability of the film strength, and precisely control the conditions of the production process.

In the case of Table 2, that is, the curves Y and Y, the peak reflectance is lower than that of the curves X and X in terms of reflection characteristics, and the low reflection region is widened.

However, as shown in FIGS. 2A and 2B, the larger the refractive index of the optical component is, the greater the reflectance is (n = 1.52) compared to the case of n = 1.59). Even in the case of high refractive index, the following problems occur.

In other words, since it is difficult to obtain sufficient spectral transmittance with a three-layer film, there is a problem in that a dielectric material of about 4 to 8 layers must be deposited, and a λ / 4 integer multiple structure is broken, which causes a very thin film. You need to go.

For example, in the case of the five anti-reflective films (described in Table 2) illustrated in Japanese Patent Publication No. 51-51283, the optical thicknesses of the three and four layers are respectively 0.12 lambda and 0.13 lambda, and in special cases 0.03 lambda There is also.

In such a case, not only accurate thickness control is difficult by the conventional optical thickness control method, but also an increase in manufacturing cost.

At this time, the present invention has been made in view of the above, and even in the case of a high refractive optical component (multilayer antireflection film having a refractive index of 1.75 to 1.85), the spectral transmittance is improved in the visible region. It is to provide a multi-layered anti-reflection film that can easily control the thin film thickness even with a conventional optical thin film thickness control method.

In order to achieve the above object, a multilayer antireflection film of the present invention is formed by depositing three layers of different materials, and has a film thickness of 0.50λ ± 0.05λ from a glass substrate group of optical components. And a third layer film of 0.25λ ± 0.025λ. Is the reference wavelength of visible light.

The present invention is a basic three-layer anti-reflection film even in the case of high refractive index by changing the refractive index and the film thickness of the deposition material of the first layer, the second layer and the third layer on the glass substrate as an optical component by the above-described forming step. Since the thickness can be easily controlled by a conventional optical thin film thickness control method, it is possible to obtain a multilayer anti-reflection film having low manufacturing cost and excellent spectral transmittance characteristics (that is, low peak reflection).

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a diagram showing the configuration of a multilayer antireflection film according to the refractive index optical part of the present invention. Table 3 shows the film thickness according to its fundamental structure.

The figure shows a three-layer antireflection film composed of a first layer film 2 and a second layer film 3 having a thickness of 0.5 lambda and a third layer film 4 having a thickness of 0.25 lambda from the glass substrate 1 which is an optical component. Consists of.

The refractive index of the substrate can be formed in the range of 1.75 to 1.85 and the refractive index selected in this embodiment is 1.8.

As can be seen from Table 3, the dielectric material of each layer is AlO, which is the first refractive index film 2, and the high refractive index material of the second layer film 3, which is a mixture of TiO and ZrO, and the third layer film 4, respectively. MgF, which is a low refractive index material, has a refractive index of n = 1.64, n = 2.13, and n = 1.39.

That is, the multilayer antireflection film of the high refractive index optical part as described above must satisfy the following conditions.

For example, when the refractive index of the substrate is n = 1.8 and λ = 510 nm,

First layer refractive index n = 1.64 nd = 0.50λ

Second layer refractive index n = 2.13 nd = 0.50λ

Third layer refractive index n = 1.39 nd = 0.25λ

Here, n, n, n denotes the refractive index of the deposition material, λ is the reference wavelength of visible light, nd, nd, nd is the refractive index of the deposition material multiplied by the physical thickness, that is, the optical film thickness.

In the present invention, since the refractive index of the substrate is formed within the range of 1.75 to 1.85, the range of the optical film thickness is described in more detail.

nd = 0.50λ ± 0.05λ

nd = 0.50λ ± 0.05λ

nd = 0.25λ ± 0.05λ.

At this time, the values of ± 0.05λ and ± 0.025λ represent an allowable range of variable values that can be allowed within the minimum value 1.75 to the maximum value 1.85 of the refractive index used in the present invention for the median value of the refractive index n = 1.8.

The multilayer anti-reflection film of the three layers provided with the above structure has an optical multiple of λ / 4 even when the refractive index is high, so that the thickness can be easily controlled by a conventional optical thin film thickness control method. It is possible to provide a reflective film which is inexpensive and has excellent spectral transmittance characteristics.

FIG. 3 is a spectral characteristic diagram showing the relationship between the wavelength and reflectance of the preferred embodiment according to the present invention shown in FIG. 1, and curve A is a glass substrate 1 with a refractive index of 1.75. ) Shows the case where the copper refractive index is 1.8, and the curve C shows the case of the copper refractive index 1.85.

In the present invention, the refractive index selected as the average value is n = 1.8, and as shown in the drawing, the overall spectral characteristics are excellent in the visible light region, and in terms of reflection characteristics, the (X, X) and (Y, Y) The peak reflectance is lower than that of the case, and the low reflectance area is also wide, which has the advantages of (X, X) and (Y, Y).

As described above, according to the present invention, the first layer film (0.54λ) is made of AlO, the second layer film (0.50λ) is made of a mixture of ZrO and TiO, and the third layer film (0.25λ) is made of MgF. In the case of a high refractive index, that is, when the refractive index of the glass substrate is formed within 1.75 to 1.85, it is possible to obtain an excellent effect that the peak reflectance is lowered in terms of reflection characteristics and the low reflection region is wider in the drawing.

In addition, the film strength can be increased, and a conventional multilayer film in which a plurality of MgF layers are interposed in the ZrO layer, or a mixture of ZrO (λ / 4) and ZrO and TiO (λ / 8) and (λ / 8) The manufacturing process is more complicated than the conventional multilayer film made of each layer of ZrO, and it can be easily controlled by the conventional optical thin film thickness control method. Automation can be achieved, and the manufacturing cost can be reduced.

Claims (1)

A first layer film 2 made of a medium refractive index material on the glass substrate 1, a second layer film 3 made of a high refractive index material on the first layer film 2, and a third made of a low refractive index material on the second layer film In the multilayer antireflection film of the high refractive index optical part composed of the layer film 4, when the refractive index of the substrate 1 is formed in the range of 1.75 to 1.85, the thickness of the first layer film 2 is 0.50 lambda ₀ ± 0.50. and λ _0, the second layer film 3 thickness is 0.50λ ₀ 0.50λ ± _0, the thickness of the third-layer film 4 is 0.25λ ₀ ± 0.025λ layers of high-refractive-index optical component, characterized in that the ₀ Anti-reflective coating. Λ ₀ : reference wavelength of visible light