JPH10148703A - Optical thin film with small absorption loss - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an optical thin film having small absorption loss without changing the film forming conditions to such hazardous conditions to decrease the absorption loss, by depositing an aluminum oxide (Al2 O3 ) as the first layer on a substrate and then alternately depositing high refractive index layers and middle or low refractive index layers as the second and succeeding layers. SOLUTION: This optical thin film is produced by depositing Al2 O3 layer 12 as the first layer from the substrate side on a substrate 11 and then alternately depositing high refractive index layers 13 and middle or low refractive index layers 14 as the second and succeeding layers on a substrate 11, and the obtd. optical thin film has small absorption loss. The high refractive index layer 13 preferably consists of titanium oxide (TiO2 ), TiO2 -contg. material or a material containing TiO2 and zirconium oxide (ZrO2 ). For example, an Al2 O3 layer 12 having 0.1λ optical film thickness is formed on a quartz glass 11 and then successively a mixture layer 13 of TiO2 and ZrO2 having 0.05λ optical film thickness and an Al2 O3 layer 14 having 0.36λ optical film thickness are formed thereon. As for the substrate 11, quartz glass having extremely small absorption loss is the most preferable.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical thin film having very little absorption loss for visible light.

[0002]

2. Description of the Related Art Almost all of current optical components are provided with an antireflection film made of a dielectric on the surface thereof. Recently, with the advancement of the film design technology, it is possible to design films with high required specifications, and these are composed of several tens of laminated films.

[0003] In many cases, strong light intensity is required, and the efficiency of the film has become important. A factor that influences the film efficiency is an absorption loss. In general, a film material having low absorption at a used wavelength is used to reduce the absorption loss. However, even when a substance having a small absorption loss is used, in the case of a multilayer film, some absorption loss phenomenon may occur near the interface of the film.

[0004] In designing a thin film using an optical constant inherent to a film material, it is impossible to investigate whether this phenomenon occurs at the design stage, and the absorption loss differs between the design value and the actual value. This causes problems in quality and performance. When such a phenomenon occurs, it is customary to change the film forming conditions to reduce the absorption loss.

In such a case, first, film forming conditions such as a film forming temperature and a film forming rate are changed to find an optimum condition for each layer. In order to satisfy the ratio, oxygen is introduced in a larger amount than usual, thereby making it difficult for substances to scramble for oxygen.

[0006]

However, when oxygen is introduced in a larger amount than usual, the risk of ignition of the oil of the vacuum pump increases. Further, the deterioration of the degree of vacuum lowers the mechanical strength and environmental resistance of the film. Therefore, the present invention has been made in view of such a problem, and it is an object of the present invention to provide an optical thin film having a small absorption loss without changing a film forming condition that involves a risk in order to reduce the absorption loss. Aim.

[0007]

According to the present invention, there is firstly provided a "aluminum oxide as a first layer counted from a substrate side on a substrate, and a high refractive index layer, an intermediate refractive index layer or a low refractive index as a second layer and thereafter. An optical thin film (Claim 1) having a small absorption loss, which is obtained by laminating alternate layers of a rate layer. Further, the present invention secondly provides an "optical thin film having low absorption loss according to claim 1 wherein the third layer counted from the substrate side is aluminum oxide (claim 2)".

[0008] The present invention is also characterized in that the high refractive index layer is made of titanium oxide, a material containing titanium oxide, or a material containing titanium oxide and zirconium oxide.
Or the optical thin film with low absorption loss according to claim 2 (claim 3) "
I will provide a.

[0009]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows Embodiment 1 of the present invention.
2 is a schematic cross-sectional view of an optical thin film having a small absorption loss. The optical thin film having a small absorption loss according to the present invention has a structure in which an Al ₂ O ₃ layer 12, a high refractive index layer 13, a low refractive index layer or an intermediate refractive index layer 14 is sequentially laminated on a substrate 11.

More specifically, an Al ₂ O ₃ layer having an optical thickness of 0.1λ and a Ti having an optical thickness of 0.05λ are formed on quartz glass.
In this configuration, a mixture layer of O ₂ and ZrO ₂ and an Al ₂ O ₃ layer having an optical thickness of 0.36λ are sequentially laminated. Although various optical glasses can be used for the substrate, quartz glass having very small absorption loss is most suitable for measuring the absorption loss of the thin film.

As materials for the high refractive index layer, zirconium oxide (ZrO ₂ ), titanium oxide (TiO ₂ ), tantalum oxide (Ta ₂ O ₅ ), niobium oxide (Nb ₂ O ₅ ), hafnium oxide (HfO ₂ ), oxide Cerium (CeO ₂ ) and the like or a mixture thereof are mentioned. Silicon oxide (SiO ₂ ), magnesium fluoride (Mg)
F ₂ ), aluminum fluoride (AlF ₃ ) and the like.

Examples of the material of the intermediate refractive index layer include aluminum oxide (Al ₂ O ₃ ) and germanium oxide (GeO ₂ ). The film forming method is performed at a film forming temperature of 300 ° C., 10 ^-4 to 10
^A film was formed by a vacuum evaporation method under a condition of a film formation rate of 5 ° / sec in a vacuum region of ^-6 Torr. FIG. 2 shows a schematic sectional view of the optical thin film of Comparative Example 1.

Optical film thickness of 0.05 on quartz glass 21
This is a configuration in which a mixture layer 22 of TiO ₂ and ZrO ₂ having λ and an Al ₂ O ₃ layer 23 having an optical thickness of 0.36 λ are sequentially laminated. FIG. 3 shows the amount of absorption loss when the thickness of the first layer of the optical thin film of Comparative Example 1 was changed. From this, it can be seen that the optical loss increases as the optical film thickness decreases, and that there is about 1% absorption loss in a practical optical film thickness range.

The absorption loss of the optical thin film of Embodiment 1 of the present invention was about 0.1%, and the absorption loss of the optical thin film of Comparative Example 1 was about 0.6%. Therefore, the optical thin film of the first embodiment of the present invention was able to significantly reduce the absorption loss as compared with Comparative Example 1. FIG. 4 is a schematic sectional view of the antireflection film according to the second embodiment of the present invention.

The antireflection film according to the second embodiment of the present invention comprises a low refractive index layer or an intermediate refractive index layer 32, 34, 3
6, 38 (first, third, fifth and seventh layers), high refractive index layers 33 and 3
This is a configuration in which seven alternate layers of 5, 37 (second, fourth, and sixth layers) are sequentially stacked. As a specific example, first on quartz glass,
An Al ₂ O ₃ layer is formed on the third and fifth layers, and TiO is formed on the second, fourth and sixth layers.
_This is a configuration in which a mixture layer of ZrO ₂ and ZrO ₂ is stacked as a seventh layer with an MgF ₂ layer.

FIG. 5 is a schematic cross section of the antireflection film of Comparative Example 2.
The figure is shown. The antireflection film of Comparative Example 2 is quartz glass
On top 41, first, third and fifth layers (42, 44, 46) Ti
O_TwoAnd ZrO_TwoLayers of the second and fourth layers (43, 4
5) Al _TwoO_ThreeThe layer is made of MgF as the sixth layer (47)._TwoLayers
This is a configuration in which the layers are stacked. Antireflection of Embodiment 2 of the present invention
The film and the antireflection film of Comparative Example 2 each satisfy optical characteristics.
Therefore, the optical film thickness is optimized.

The method of forming the anti-reflection film of the second embodiment of the present invention and the method of forming the anti-reflection film of the comparative example 2 were performed in the same manner as the optical thin film of the first embodiment of the present invention. FIG. 6 shows the spectral reflection characteristics of the antireflection film of the second embodiment of the present invention (broken line) and the antireflection film of the second comparative example (solid line). It can be seen that there is no difference in the spectral characteristics of the antireflection film of Example 2.

The absorption loss of the anti-reflection coating of the second embodiment of the present invention was about 0.1%, and the absorption loss of the anti-reflection coating of Comparative Example 2 was about 0.9%. Thus, the absorption loss can be reduced by providing aluminum oxide on the first layer counted from the substrate side on the substrate, and the spectral characteristics are not affected by optimizing the optical film thickness of each layer. You can see that it was not given.

[0019]

As described above, the optical thin film according to the present invention can significantly reduce the absorption loss by providing aluminum oxide as the first layer on the substrate, counting from the substrate side. By optimizing the thickness, the spectral characteristics are not affected at all.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of an optical thin film according to a first embodiment of the present invention.

FIG. 2 is a schematic sectional view of an optical thin film of Comparative Example 1.

FIG. 3 shows the amount of absorption loss when the thickness of the first layer of the optical thin film of Comparative Example 1 was changed.

FIG. 4 is a schematic sectional view of an antireflection film according to a second embodiment of the present invention.

FIG. 5 is a schematic sectional view of an antireflection film of Comparative Example 2.

FIG. 6 is a spectral reflection characteristic diagram of the antireflection film (dashed line) of Embodiment 2 of the present invention and the antireflection film (solid line) of Comparative Example 2.

[Explanation of symbols]

11, 21, 31, 41 ... optical substrate 12, 23, 43, 45 ... aluminum oxide layer 13, 33, 35, 37 ... high refractive index layer 14, 32, 34, 36, 38 ... and intermediate refractive index layer or low refractive index layer 22,42,44,46 ··· TiO ₂ and mixtures layer 47 · · · MgF ₂ and ZrO ₂

Claims (3)

[Claims] 1. An absorption structure in which aluminum oxide is formed as a first layer on a substrate and an alternate layer of a high refractive index layer, an intermediate refractive index layer or a low refractive index layer is formed on the second and subsequent layers counted from the substrate side. Optical thin film with low loss. 2. The optical thin film according to claim 1, wherein the third layer counted from the substrate side is aluminum oxide. 3. The optical thin film according to claim 1, wherein said high refractive index layer is made of titanium oxide, a material containing titanium oxide, or a material containing titanium oxide and zirconium oxide.