JPH04247864A - Silicon dioxide thin film - Google Patents

Abstract

PURPOSE:To improve the durability to a high temp. and high humidity without applying a change to the refractive index of the silicon dioxide itself. CONSTITUTION:This silicon dioxide thin film is constituted by using the silicon dioxide contg. 0.5 to 15wt.% tantalum oxide as a low-refractive index material coating a substrate. The durability of the silicon dioxide thin film is greatly improved without changing the refractive index of the silicon dioxide thin film if the silicon dioxide thin film is constituted in such a manner. In addition, the silicon dioxide thin film is adequate as an optical thin film as well.

Description

[Detailed description of the invention]

[Purpose of the invention]

0001

BACKGROUND OF THE INVENTION 1. 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 In general, silicon dioxide (SiO2) thin films are widely used as protective films for substrates with aluminum reflective surfaces and as low refractive index materials in optical multilayer films. When this SiO2 thin film is deposited, for example, as a protective film on an aluminum mirror, a vacuum evaporation method is mainly adopted, and the evaporation means include direct evaporation using electron beam heating, or reactive evaporation using resistance heating in an oxygen atmosphere. be.

However, the S film formed by the above method
All iO2 thin films have the following drawbacks.

Specifically, as shown in FIG. 9, a 0.2 μm SiO2 protective film is deposited on an aluminum mirror surface, and a 0.2 μm aluminum oxide (Al2O2) protective film is deposited on the aluminum mirror surface.
3) The product coated with a thin protective film is exposed to high temperature and high humidity
When left in an atmosphere with a temperature of 50°C and humidity of 90%,
As is clear from the change in the maximum reflectance of both thin films, SiO2
It can be seen that the thin film has extremely poor moisture resistance compared to the Al2O3 thin film. Therefore, as a mere protective film, S
A possible improvement measure is to use an Al2 O3 thin film instead of the iO2 thin film.

[0005]

[Problem to be solved by the invention] However, the above A
When using an l2O3 thin film as a low refractive index material for optical thin films (especially cold mirrors, bandpass filters, etc.), the refractive index of Al2O3 is 1.63 and SiO2
1.46, so even if the multilayer film has the same number of layers, it has the disadvantage that the width of the reflective region and reflectance are lower than that of a multilayer film containing SiO2.

The present invention has been made in view of the above circumstances, and while conventional SiO2 thin films have a low refractive index, they have the disadvantage of poor moisture resistance. Al2 O3 At a high temperature comparable to or higher than that of a thin film,
An object of the present invention is to provide a silicon dioxide thin film having durability against high humidity.

[Configuration of the invention]

[0008]

[Means for Solving the Problems] In order to achieve the above object, the present invention is characterized in that silicon dioxide containing 0.5 to 15% by weight of tantalum oxide is used as a low refractive index material to coat the substrate. It is something to do.

[0009]

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

0010

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

First, as shown in FIG. 1, silicon dioxide (Si) as a low refractive index material is deposited on a substrate 1 made of an aluminum mirror surface.
Tantalum oxide (Ta2O5) was mixed with O2) and deposited, and the refractive index of the thin film 2 was investigated. FIG. 2 shows the mixing weight ratio of SiO2 and Ta2O5 and the corresponding refractive index of the SiO2 thin film 2.
Thin film 2 was formed by vacuum evaporation under the following evaporation conditions.

(1) Degree of vacuum 1×10−4 to 5×10−4T
orr (1.3 to 6.7 x 10-2 Pa) (2) Substrate temperature 250 to 300°C (3) Evaporation source Electron beam (4) Evaporation agent A mixture of SiO2 and Ta2 O5.

[0013] Here, the melting point of SiO2 is 1700°C,
Since the melting point of Ta2O5 is relatively close to 1500°C, the evaporation of these mixtures is easy, and T
A thin film 2 of SiO2 containing a2 O5 is deposited. Furthermore, a similar SiO2 thin film 2 can be easily deposited by a binary vapor deposition method different from the above-mentioned vapor deposition method.

As shown in FIG. 2, a thin film 2 of SiO2 containing Ta2O5 is formed by adding Ta2O5 as an additive.
It has been found that when the amount of 5 added is 15% by weight or less based on SiO2, the refractive index shows a value almost equal to 1.46 of SiO2, and the refractive index does not change.

Next, the durability of the SiO2 thin film 2 in a high temperature and high humidity environment was evaluated when the amount of Ta2O5 added was 15% by weight or less, and the evaluation results shown in FIG. 3 were obtained. That is, in FIG. 3, a substrate 1 made of an aluminum mirror surface is coated with 0.
2μm SiO2 thin film 2 (added Ta2O5
The amounts of are 0.3, 0.5, 1, 3, 7, 12, respectively.
This graph shows the change in the maximum reflectance of the film when an aluminum mirror coated with a protective film of 50°C and 15% by weight is left in an atmosphere of high temperature and humidity (temperature 50°C, humidity 90%). .

As shown in FIG. 3, compared to the Al2 O3 protective film, the SiO2 thin film 2 with added Ta2 O5 in an amount of 0.3 wt.
The reflectance was 85 after 200 hours compared to 250 hours for the protective film.
%, making it unusable, and the SiO2 protective film containing 0.5 to 15 wt.
It was found that durability comparable to that of the Al2 O3 protective film was obtained at 5% by weight, and that the durability increased as the amount added increased.

[0017] Therefore, if the amount of Ta2O5 added is 0
．． If it is less than 5% by weight, the durability will be significantly lowered as described above compared to the Al2O3 protective film, and if it exceeds 15% by weight, the refractive index will increase, making it difficult to use it as an optical thin film. In this case, the width of the reflection region and the reflectance will be reduced. In this way, T to the SiO2 thin film 2
The amount of a2 O5 added is preferably 0.5 to 15% by weight.

Next, an example in which the SiO2 thin film 2 containing Ta2 O5 is applied as a low refractive index material to an optical thin film, such as a multilayer film in a cold mirror, will be described with reference to FIGS. 4 to 8.

In FIG. 4, the reflective substrate 3 is a reflective mirror for a halogen lamp made of, for example, hard glass, and has a concave portion 4 in the shape of a paraboloid of revolution expanded on one side. At the center of this recess 4 is a halogen lamp 5 that serves as a light source.
A multilayer film 6, which is a visible light reflecting and infrared transmitting film, is further applied on the inner surface of the recess 4.

The multilayer film 6 is made by laminating 17 layers of Ta2O5-containing SiO2 thin film 2 as a low refractive index material and titanium dioxide (TiO2: refractive index 2.31) as a high refractive index material. TiO2 film formed by
/SiO2 consisting of alternating layers. This multilayer film 6
A film was formed by a vacuum evaporation method under the evaporation conditions shown below.

(1) Degree of vacuum 1×10−4 to 5×10−4T
orr (1.3 to 6.7×10-2 Pa) (2) Substrate temperature 250 to 300°C (3) Evaporation source Electron beam.

Table 1 shows TiO2 /SiO2 alternating layers made of SiO2 containing 5% by weight of Ta2O5, Table 2
TiO2 by SiO2 without Ta2O5 in
/SiO2 alternating layers, and Al as a comparative example in Table 3.
TiO2 /Al2 with 2 O3 as a low refractive index substance
The film configurations of the O3 alternating layers are shown. These alternating films were formed under the above deposition conditions, and the spectral transmittance characteristics of these alternating films are shown in FIGS. 5 to 7.

[0023]

[Table 1]

[0024]

[Table 2]

[0025]

[Table 3] As is clear from FIGS. 5 to 7, Ta2O
TiO2 / made of SiO2 containing 5% by weight of 5
The spectral transmittance characteristics of the SiO2 alternating layers are similar to those of Ta2O5
There is almost no difference in optical properties from the spectral transmittance characteristics of TiO2 /SiO2 alternating layers made of SiO2 containing no SiO2 or TiO2 /Al2 O3 alternating layers. Therefore, it was found that the SiO2 thin film containing Ta2O5 can be used as an optical thin film.

Furthermore, the durability of each of the alternating layers of the above film structure was evaluated by a sunshine weather meter test under the following conditions.

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

The evaluation results by the sunshine weather meter test are shown in FIG. 8. As shown in FIG.
The SiO2 thin film containing a2O5 is SiO2
It was found that the durability against high temperature and high humidity was significantly improved compared to a single thin film or an Al2O3 thin film.

In the above embodiments, the method for forming the multilayer film was vacuum evaporation; however, the method is not limited to this, and may also include ion plating, ion assist, CVD (chemical vapor deposition), etc.
Other forming methods such as the Vapor Deposition method may also be used.

Further, in the above application example, an example was explained in which the multilayer film was applied to a visible light reflective infrared transmitting film in a cold mirror, but the invention is not limited to this, for example, it is applied to a film formed on the outer surface of a halogen light bulb that transmits visible light. It may be applied to a visible light transmitting infrared reflecting film that returns infrared rays to a filter, or an interference filter film that selectively transmits or reflects light in a specific wavelength range.

Furthermore, 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.

[0032]

Effects of the Invention As detailed above, the silicon dioxide thin film of the present invention has a structure in which silicon dioxide containing 0.5 to 15% by weight of tantalum oxide is used as the low refractive index substance coating the substrate. By doing so, durability can be significantly improved without changing the refractive index of silicon dioxide itself.

Furthermore, the optical properties required for cold mirrors, band-pass filters, etc. can be obtained, and the film is sufficiently suitable as an optical thin film for cold mirrors, band-pass filters, etc.

[Brief explanation of the drawing]

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

FIG. 2 is a curve diagram showing changes in the refractive index of a SiO2 thin film with respect to the mixing ratio of Ta2O5 added to SiO2.

FIG. 3 is a curve diagram showing the maximum reflectance of a SiO2 thin film added with Ta2O5 when left in a high temperature and high humidity environment.

FIG. 4 is a sectional view showing a cold mirror to which the present invention is applied.

FIG. 5 is a curve diagram showing the spectral transmittance characteristics of a TiO2/SiO2 alternating layer made of SiO2 containing 5% by weight of TiO2 and Ta2O5.

[Figure 6] TiO2 by TiO2 and SiO2 alone
FIG. 3 is a curve diagram showing spectral transmittance characteristics of alternating layers of /SiO2.

FIG. 7 is a curve diagram showing spectral transmittance characteristics of TiO2/Al2O3 alternating layers.

FIG. 8 is a curve diagram showing the highest reflectance according to a sunshine weather meter test for alternating layers having the film configurations shown in Tables 1 to 3;

FIG. 9 is a curve diagram showing the change in maximum reflectance of a conventional SiO2 protective film and an Al2O3 protective film at high temperature and high humidity.

[Explanation of symbols]

1...Substrate 2...SiO2 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 15% by weight of tantalum oxide is used as a low refractive index material covering a substrate.