JPH0588005A - Silicon dioxide thin film - Google Patents

Abstract

(57) [Summary] [Purpose] To improve durability against high temperature and high humidity without changing the refractive index of silicon dioxide itself. [Structure] Silicon dioxide containing 0.5 to 10% by weight of metal tin is used as a low refractive index material for covering the substrate. With this structure, the durability of the silicon dioxide thin film is significantly improved without changing the refractive index of the silicon dioxide thin film, and the silicon dioxide thin film is suitable as an optical thin film.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a silicon dioxide thin film for coating a substrate such as a reflecting mirror.

[0002]

_2. Description of the Related Art Generally, a silicon dioxide (SiO ₂ ) thin film is widely used as a protective film for a substrate having aluminum as a reflecting surface and a low refractive index substance in an optical multilayer film. When this SiO ₂ thin film is applied as a protective film of, for example, an aluminum mirror, a vacuum vapor deposition method is mainly adopted, and its vapor deposition means is direct vapor deposition by electron beam heating or reactive vapor deposition by resistance heating in an oxygen atmosphere. There is.

However, S formed by the above means
Each of the iO ₂ thin films has the following drawbacks.

That is, as shown in FIG. 10, an aluminum mirror surface coated with a protective film of 0.2 μm of SiO ₂ and an aluminum mirror surface of 0.2 μm of aluminum oxide (Al
₂ O ₃ ) When a thin film protective film is left in an atmosphere of high temperature and high humidity (temperature 50 ° C, humidity 90%), it becomes clear from the change in the maximum reflectance of both thin films. Si
It can be seen that the O ₂ thin film is extremely inferior in moisture resistance as compared with the Al ₂ O ₃ thin film. Therefore, as a simple protective film, Si
The use of an Al ₂ O ₃ thin film instead of the O ₂ thin film is considered as a temporary improvement measure.

[0005]

However, the above-mentioned A
When the l ₂ O ₃ thin film is used as an optical thin film as a low refractive index material (particularly, a cold mirror or a bandpass filter), the refractive index of Al ₂ O ₃ is 1.63 and that of SiO ₂ is 1.4.
Since it is considerably higher than that of No. 6, even if it is a multilayer film having the same number of layers, it has a drawback that the width of the reflection region and the reflectance are lowered as compared with the multilayer film containing SiO ₂ .

The present invention has been made in view of the above circumstances and has durability against high temperature and high humidity which is equal to or higher than that of the Al ₂ O ₃ thin film without changing the refractive index of the SiO ₂ thin film. The present invention aims to provide a silicon dioxide thin film having

[0007]

In order to achieve the above object, the present invention is characterized in that silicon dioxide containing 0.5 to 10% by weight of metallic tin is used as a low refractive index material for coating a substrate. To do.

[0008]

Since the present invention is constructed as described above, the durability of the silicon dioxide thin film is remarkably improved without changing the refractive index of the silicon dioxide thin film.

[0009]

Embodiments of the present invention will be described below with reference to the drawings.

First, as shown in FIG. 1, silicon dioxide (SiO 2) as a low refractive index material is formed on a substrate 1 made of an aluminum mirror surface.
₂ ) mixed with metallic tin (Sn) and deposited to form a thin film 2
The refractive index of was investigated. FIG. 2 shows the mixing weight ratio of SiO ₂ and Sn and the corresponding refractive index of the SiO ₂ thin film 2. The thin film 2 was formed by the vacuum evaporation method under the following vapor deposition conditions.

(1) Degree of vacuum 1 × 10 ^{-4 to} 5 × 10 ^-4 To
rr (1.3 to 6.7 × 10 ^-2 Pa) (2) Substrate temperature 250 to 300 ° C. (3) Evaporation source electron beam (4) Evaporating agent Mixture of SiO ₂ and Sn.

Further, a similar thin film 2 of SiO ₂ can be easily deposited by a binary vapor deposition method different from the above vapor deposition method.

As shown in FIG. 2, SiO containing Sn
Thin film 2 of _2, the amount of which is additive Sn is in respect SiO ₂ 10 wt% or less of SiO ₂ refractive index 1.4
It was found that it showed a value almost equal to 6 and did not change the refractive index.

Subsequently, the durability of the SiO ₂ thin film 2 in an environment of high temperature and high humidity when the added amount of Sn was 10% by weight or less was evaluated, and the evaluation results shown in FIG. 3 were obtained. That is, FIG. 3 shows that a 0.2 μm SiO ₂ thin film 2 (the amount of Sn added is 0.
3%, 0.5%, 1%, 3%, 7%, and 10% by weight) aluminum mirrors with respective protective films formed are left in an atmosphere of high temperature and high humidity (temperature 50 ° C., humidity 90%) It shows a change in the maximum reflectance of the film.

As shown in FIG. 3, as compared with the Al ₂ O ₃ protective film, the protective film of the SiO ₂ thin film 2 in which the amount of Sn added is 0.3% by weight is the same as the Al ₂ O ₃ protective film of 250. After 240 hours, the reflectance was reduced to 85% and the sample became unusable, and the addition amount of Sn was 0.5 to 10% by weight.
It has been found that the O ₂ protective film has the same durability as the Al ₂ O ₃ protective film at 0.5% by weight, and the durability increases as the amount of addition increases.

Therefore, the addition amount of Sn is 0.5% by weight.
When it is less than 10% by weight, the durability is remarkably lowered as compared with the Al ₂ O ₃ protective film, and when it exceeds 10% by weight, the refractive index becomes high, and the film is used as an optical thin film. In this case, the width and reflectance of the reflection area will be reduced.
Thus, the amount of Sn added to the SiO ₂ thin film 2 is preferably 0.5 to 10% by weight.

Further, 0.2 is formed on the substrate 1 made of an aluminum mirror surface.
A high-temperature and high-humidity aluminum mirror having each protective film in which tin dioxide (SnO ₂ ) was added to the μm SiO ₂ thin film 2 (the amount of each added SnO ₂ was 1, 5, 10 and 15% by weight) FIG. 4 shows the change in the maximum reflectance of the film when left in the atmosphere of (temperature 50 ° C., humidity 90%). Here, the protective film in which SnO ₂ was added to the SiO ₂ thin film 2 was formed by the vacuum evaporation method under the following vapor deposition conditions.

(1) Degree of vacuum 1 × 10 ^{-4 to} 5 × 10 ^-4 To
rr (1.3 to 6.7 × 10 ^-2 Pa) (2) Substrate temperature 250 to 300 ° C. (3) Evaporation source electron beam (4) Evaporating agent A mixture of SiO ₂ and SnO ₂ .

As is clear from FIGS. 3 and 4, Si
It has been found that the protective film obtained by adding metallic tin (Sn) to the O ₂ thin film 2 is superior in durability to the protective film obtained by adding tin oxide (SnO ₂ ). It is presumed that this is because the number of non-bridging oxygen remaining in silicon oxide (SiO ₂ ) can be reduced in metallic tin (Sn) compared with tin oxide (SnO ₂ ), and chemical stability is improved. To be done.

Next, an example in which the Sn-containing SiO ₂ thin film 2 is applied as an optical thin film as a low refractive index material, for example, a multilayer film in a cold mirror will be described with reference to FIGS. 5 to 9.

In FIG. 5, a reflecting substrate 3 is a reflecting mirror for a halogen lamp, which is made of, for example, hard glass, and has a recessed portion 4 of a parabolic shape whose one surface is expanded. A halogen lamp 5 serving as a light source is mounted in the center of the recess 4, and a multilayer film 6 which is a visible-light-reflecting infrared-transmissive film is deposited on the inner surface of the recess 4.

The multilayer film 6 is a Sn-containing SiO ₂ thin film.
2 is a low refractive index material, and titanium dioxide (TiO ₂ :
It has a high refractive index material having a refractive index of 2.31) and is composed of 17 alternating layers of TiO ₂ / SiO ₂ alternating layers. This multilayer film 6 was formed by a vacuum evaporation method under the following evaporation conditions.

(1) Degree of vacuum 1 × 10 ^{-4 to} 5 × 10 ^-4 To
rr (1.3 to 6.7 × 10 ^-2 Pa) (2) Substrate temperature 250 to 300 ° C (3) Evaporation source electron beam.

[0024] Table TiO ₂ / SiO ₂ alternating layer by SiO ₂ which contains Sn 3% by weight 1, TiO ₂ / SiO ₂ alternating layer by SiO ₂ containing no Sn in Table 2, and Table 3
In addition, as a comparative example, TiO using Al ₂ O ₃ as a low refractive index material
The film structures of the ₂ / Al ₂ O ₃ alternating layers are shown respectively. These alternating films are formed under the above vapor deposition conditions, and the spectral transmittance characteristics of these alternating films are shown in FIGS. 6 to 8.

[0025]

[Table 1]

[0026]

[Table 2]

[0027]

[Table 3]

As is apparent from the spectral transmittance characteristics shown in FIGS. 6 to 8, the spectral transmittance characteristics of the TiO ₂ / SiO ₂ alternating layer made of SiO ₂ containing 3% by weight of Sn are SiO ₂ containing no Sn _2. TiO ₂ / SiO ₂ alternating layers and T
Almost no difference is observed between the spectral transmittance characteristics of the alternating iO ₂ / Al ₂ O ₃ layer and the optical characteristics. Therefore, it was found that the SiO ₂ thin film containing Sn can be used as an optical thin film.

Further, with respect to each of the alternating layers having the above-mentioned film constitution, the durability was evaluated by the sunshine weather meter test under the following conditions.

(1) Temperature 63 ± 3 ° C. (2) Water jet conditions 18 minutes during 120 minutes irradiation.

The evaluation results by the sunshine weather meter test are shown in FIG. 9. As is clear from FIG. 9, the SiO ₂ thin film containing Sn has a higher temperature than the thin film of SiO ₂ alone or the Al ₂ O ₃ thin film.・ It was confirmed that the durability against high humidity was remarkably improved.

In the above embodiment, the method for forming the multilayer film is the vacuum evaporation method, but the method is not limited to this, and other forming methods such as an ion plating method and an ion assist method may be used.

Further, in the above application example, an example in which the multilayer film is applied to the visible light reflecting infrared ray transmitting film in the cold mirror has been described. It may be applied to a visible light transmitting infrared reflecting film that returns infrared rays to a filament or an interference filter film that selectively transmits or reflects light in a specific wavelength range.

Further, the present invention is not limited to the above-mentioned embodiments, and it goes without saying that various modifications can be made without departing from the gist of the present invention.

[0035]

As described above in detail, according to the silicon dioxide thin film of the present invention, silicon dioxide containing 0.5 to 10% by weight of metallic tin is used as the low refractive index material for coating the substrate. As a result, the durability can be significantly improved without changing the refractive index of silicon dioxide itself.

Further, the optical characteristics required for the cold mirror, the bandpass filter, etc. can be obtained, and it can be sufficiently adapted as an optical thin film for the cold mirror, the bandpass filter, etc.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a substrate made of an aluminum mirror according to an embodiment of the present invention.

FIG. 2 shows the ratio of SiO to the mixture ratio of Sn added to SiO ₂ .
FIG. 3 is a curve diagram showing changes in the refractive index of _two thin films.

FIG. 3 is a curve diagram showing the maximum reflectance of a SiO ₂ thin film containing Sn when left in a high temperature and high humidity environment.

FIG. 4 is a curve diagram showing the maximum reflectance of a SiO ₂ thin film added with SnO ₂ when left in a high temperature and high humidity environment.

FIG. 5 is a sectional view showing a cold mirror to which the present invention is applied.

FIG. 6 TiO ₂ / SiO ₂ + Sn (Sn: 3% by weight)
It is a curve figure which shows the spectral transmittance characteristic of an alternating layer.

FIG. 7 is a curve diagram showing a spectral transmittance characteristic of a TiO ₂ / SiO ₂ alternating layer.

FIG. 8 is a curve diagram showing a spectral transmittance characteristic of a TiO ₂ / Al ₂ O ₃ alternating layer.

FIG. 9 is a curve diagram showing the maximum reflectance by a sunshine weather meter test for alternate layers having the film configurations shown in Tables 1 to 3.

FIG. 10 is a curve diagram showing changes in the maximum reflectance of a conventional SiO ₂ protective film and an Al ₂ O ₃ protective film at high temperature and high humidity.

[Explanation of symbols]

1… Substrate 2… SiO ₂ thin film 3… Reflective substrate (substrate) 6… Multilayer film

Claims (1)

[Claims] 1. A silicon dioxide thin film characterized in that silicon dioxide containing 0.5 to 10% by weight of metallic tin is used as a low refractive index material for coating a substrate.