JPS6281605A - Optical filter made of multilayered dielectric film and its production - Google Patents

Abstract

PURPOSE:To obtain an optical filter having high stability and reliability for a long period by laminating an amorphous SiO2 layer and an anatase type TiO2 layer on a substrate. CONSTITUTION:A multilayered film contg. an amorphous SiO2 layer and an amorphous TiO2 layer is formed on a substrate and heat treated at 190-500 deg.C in the air to convert the amorphous TiO2 layer into an anatase type TiO2 layer. Thus, a very stable optical filter made of a multilayered film is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION Object of the Invention (Field of Industrial Application) The present invention relates to a dielectric multilayer optical filter, and particularly to an environmentally resistant dielectric multilayer optical filter using SiO2 and TiO2.

(Prior art) Conventionally, multilayer optical filters using dielectric materials, especially SiO
The optical properties of optical filters using □ film and TiO□ film are as follows:
It is known to be significantly affected by changes in the environment.

This means that optical properties measured under one environment may differ from those measured under another environment.
For example, this means that it will be different under the actual environment of use, which is a major drawback of multilayer optical filters.

In addition, when these optical filters are processed such as cutting and back polishing, they are affected by heat and moisture, causing variations in optical characteristics, making multilayer optical filters difficult to use. That is, although a multilayer film is usually formed by vacuum deposition,
By introducing air into the vacuum chamber after vapor deposition, the center wavelength of the filter shifts by 20 nm or more longer, and due to changes over time, the wavelength shifts further by about 40 nm longer. It is believed that this is because the vapor deposited film is a porous film that absorbs water vapor and the like.

On the other hand, it has been proposed to stabilize the multilayer film by manufacturing it by electron beam evaporation and then annealing it in air (Japanese Patent Laid-Open No. 13780-1989).
No. 9). In this method, the substrate temperature is maintained at about 350° C., so the deposited layer is partially crystallized, has low deposition strength, and has internal strain, so it is attempted to stabilize it by annealing. However, the porous structure of the film did not change, and it was not possible to prevent the center wavelength from shifting from about 5 nm or more shorter when dry to about the same length when rainy.

The present applicant had previously invented a high-frequency ion bombardment device (Japanese Patent Application No. 74306/1983), which does not require heating of the substrate and has a honey-like adhesive that is not affected by humidity or other factors. is obtained. However, this film is amorphous and has the disadvantage that its properties change when heated.

(Problems to be Solved by the Invention) The present invention aims to provide a multilayer optical filter that is hardly affected by the environment described above and has a structure that can be manufactured extremely easily.

Structure of the Invention (Means for Solving the Problems) The present invention provides a method of manufacturing a duck in which a multilayer film including an amorphous 5in2 film and an amorphous TiO2 film is laminated on a substrate, and the temperature of the duck in the air is 190°C or higher and 500°C or lower. The present invention is characterized in that an extremely stable multilayer optical filter including an amorphous SiO2 film and anatase TlO2 film is obtained by transforming the amorphous TiO film into an anatase TlO2 film by heat treatment in a temperature range.

(Function) S deposited without heating the substrate by a plasma ion process using a high frequency ion bombardment device.
It was confirmed by X-ray diffraction that both of the multilayer films made of iO and TiO were amorphous. Although this multilayer film is a valuable filter in itself, it
It has the disadvantage that its optical properties change when heated to 90° C. or higher.

When this multilayer film is heated in a temperature range of 190° C. or more and 500° C. or less, amorphous TiO in the multilayer film undergoes phase transition to anatase TiO2. After being transformed into this anatase TlO2 film, it is stable even when heated at 500°C. Therefore, by heating to this extent, a thermally extremely stable filter can be obtained.

(Example) Amorphous Si○2 and amorphous TiO2 were deposited by a plasma ion process using a high-frequency ion bombardment device as described above without heating the substrate.
Both films are amorphous in the multilayer film consisting of
Confirmed by line diffraction. Curve (a) in Figure 1
is an example of the spectral transmittance characteristics of a bandpass filter manufactured in this manner, and FIG. 2 is an example of the measurement of its X-ray diffraction pattern, showing that it has a typical amorphous structure.

This filter does not deteriorate in air at temperatures below approximately 185°C, and can be used at temperatures of 85°C, humidity of 85%, and 50°C.
Even after a 0-hour high-temperature, high-humidity test, a 2-hour temperature cycle test at 80°C and -40°C, and a 10-cycle temperature cycle test, there is no significant change in its spectral properties. Multilayer films have been shown to be excellent filters.

However, it has been found that when this filter is heated in air to a temperature of about 190° C. or higher, anatase TiO□ grows within the amorphous TiO2 layer. At 200° C., several tens of hours are required to complete the phase transition of the amorphous TiO layer, while at 250° C., several hours are sufficient. Figure 3 shows an example of an X-ray diffraction pattern after heat treatment in air at 250°C for 5 hours, and the spectral characteristics after such a phase transition are as shown in curve (b) in Figure 1. It was confirmed that there was a change.

A dielectric multilayer optical filter that has undergone such heat treatment is
A dielectric multilayer film that exhibits sufficient environmental resistance without causing significant changes in spectral characteristics even after heating to 500°C in air, the high temperature and high humidity test, and the temperature cycle test described above. I was able to confirm that it was an optical filter.

Effects of the Invention According to the present invention, with the above structure, the dielectric multilayer optical filter also has its constituent SiO□ film and TiO2 film laminated as an amorphous SiO□ film and an amorphous TiO2 film, and then heats this as a whole. Through the simple process of 1. This makes it possible to easily obtain a dielectric multilayer optical filter that does not require any special treatment, has optical characteristics that do not change even when exposed to various environments, is extremely reliable, and is stable over a long period of time. .

[Brief explanation of drawings]

Figure 1 is a spectral characteristic curve diagram of a dielectric multilayer filter;
3 and 3 are X-ray diffraction pattern diagrams of the multilayer film before and after heat treatment, respectively. Patent applicant Japan Vacuum Optical Co., Ltd. Applicant agent Patent attorney Fumio Sato/1IJl*, U1 Ml Figure

Claims (1)

[Claims] 1) Amorphous SiO_2 film and anatase T on the substrate
Dielectric multilayer optical filter characterized by laminating iO_2 films 2) After laminating an amorphous SiO_2 film and an amorphous TiO_2 film on a substrate, heating at 190°C or higher in air
By heat treatment at a temperature range of 500℃ or less,
The above amorphous TiO_2 film was converted into anatase TiO_2
A method for producing a dielectric multilayer optical filter characterized by altering it into a film