JPH07180048A - Production of optical film - Google Patents

Abstract

PURPOSE:To obtain an optical film having no absorption and a low refractive index by forming a film of AlF3 or MgF2 by sputtering using aluminum or magnesium as a target material and chlorine-contg. gas, fluorine-contg. gas and inert gas as process gases. CONSTITUTION:Aluminum or magnesium as a target material is allowed to react with chlorine-contg. gas to form a chlorine compd. This chlorine compd. is allowed to react with fluorine-contg. gas and the fluorine is substd. for the chlorine to form a fluoride. Since AlF3 or MgF2 is formed through the two-stage reaction process, the objective optical film having a refractive index of <=1.4 and no absorption is formed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing an optical film having a low refractive index of 1.4 or less.

[0002]

2. Description of the Related Art Conventionally, when forming an optical thin film typified by an antireflection film, a vacuum vapor deposition method has been generally used in which a film forming material is heated by an electron beam or the like and adhered to a substrate. In this case, one of a material having a low refractive index such as MgF ₂ or a material having a high refractive index such as ZrO ₂ , TiO ₂ , Ta ₂ O ₅ or a multilayer film in which these materials are combined is used. However, in recent years, since more efficient production has been required, even with these optical thin films, mass productivity, labor saving of processes, stabilization of quality, cost reduction, etc. can be achieved as compared with the vacuum deposition method. In view of this, there is an increasing demand for coating by a sputtering method, which is advantageous in terms of the aspect.

Above all, as a method of forming a film having a low refractive index of 1.4 or less by a sputtering method,
For example, the invention described in JP-A-4-289165 has been proposed. The above invention is a method of sputtering an alkaline earth metal fluoride film such as MgF ₂ using a mixed gas of an inert gas such as Ar and a fluorine-based gas such as CF ₄ .

[0004]

However, in the vacuum deposition method, M, which is used as the most general low refractive index material, is used.
When gF ₂ is formed by a sputtering method, the composition ratio of the film deviates from the stoichiometric ratio and becomes a Mg-rich film, so that absorption in the visible region occurs in the film.

In order to solve this drawback, the above-mentioned Japanese Patent Laid-Open No. 4-2 is used.
In the invention described in 89165, sputtering is performed using a mixed gas of an inert gas and a fluorine-based gas. However, when fluoride is used as the target,
It cannot be said that the introduction of a fluorine-based gas suppresses the dissociation of fluorine. Moreover, when a fluoride is used as a target, it is also very difficult to increase the film formation rate.

Therefore, the present invention was developed in view of the above-mentioned drawbacks of the prior art. A film having a low refractive index of 1.4 or less and no absorption in the visible region is formed by a sputtering method. An object is to provide a method for producing an optical film that can be formed into a film.

[0007]

According to the present invention, aluminum (Al) or magnesium (Mg) is used as a target for film formation, and a gas containing chlorine, a gas containing fluorine and an inert gas are simultaneously used as a process gas. The film is introduced into the film forming chamber and is sputtered to form AlF ₃ or Mg.
This is a method of forming F ₂ into a film.

[0008]

In the formation of the fluoride, first, the chlorine-based gas and the target material react with each other to form a chlorine compound, the fluorine gas reacts with the chlorine compound, chlorine is replaced with fluorine, and the fluoride is formed. Through such a two-step reaction process, it is possible to form an optical film of AlF ₃ , MgF ₂ or the like having a refractive index of 1.4 or less and no absorption by a sputtering method.

[0009]

Example 1 FIG. 1 is a graph showing the spectral characteristics of the antireflection film formed in this example. A glass substrate having a refractive index of 1.52 was set in a vacuum chamber and evacuated to 1 × 10 ^-3 Pa, and then CCl ₄ , with a partial pressure of 1 × 10 ^-1 Pa, 1 × 10 ^-1 Pa.
CF ₄ and 5 × 10 ^-2 Pa Ar were introduced into the vacuum chamber through MFC (gas flow controller). The substrate was not heated, and Al was used as a target to form an AlF ₃ film by a DC (direct current) or RF (high frequency) sputtering method with an input power of 200 W.

Film formation was performed until the optical film thickness reached 130 nm while monitoring the film thickness with an optical film thickness meter. When the refractive index of the formed film was measured by an ellipsometer, it was 1.385 at a wavelength of 500 nm. The absorption of the film in the visible region was 1% or less. This film has the same optical performance as a MgF ₂ single-layer antireflection film formed by ordinary vacuum deposition.

[0011]

Example 2 FIG. 2 is a graph showing the spectral characteristics of the antireflection film formed in this example. A glass substrate having a refractive index of 1.52 was set in a vacuum chamber and evacuated to 1 × 10 ^-3 Pa, and then CCl ₄ , with a partial pressure of 1 × 10 ^-1 Pa, 1 × 10 ^-1 Pa.
CF ₄ and Ar of 5 × 10 ^-2 Pa were introduced into the vacuum chamber through the MFC. The substrate is not heated and the target is M
Mg was used to form a MgF ₂ film by DC or RF sputtering with an input power of 200 W.

Film formation was performed until the optical film thickness reached 130 nm while monitoring the film thickness with an optical film thickness meter. When the refractive index of the formed film was measured by an ellipsometer, it was 1.390 at a wavelength of 500 nm. The absorption of the film in the visible region was 1% or less. This film has the same optical performance as a MgF ₂ single-layer antireflection film formed by ordinary vacuum deposition.

[0013]

Example 3 FIG. 3 is a graph showing the spectral characteristics of the antireflection film formed in this example. After setting a glass substrate having a refractive index of 1.7 in a vacuum chamber and evacuating to 1 × 10 ⁻³ Pa,
BCl _{3 having} a partial pressure of 1 × 10 ⁻¹ Pa and C having a partial pressure of 1 × 10 ⁻¹ Pa
F ₄ and 5 × 10 ⁻² Pa Ar were introduced into the vacuum chamber through the MFC. The substrate was not heated, and Mg was used as a target to form a MgF ₂ film by a DC or RF sputtering method with an input power of 200 W.

Film formation was performed until the optical film thickness reached 130 nm while monitoring the film thickness with an optical film thickness meter. When the refractive index of the formed film was measured by an ellipsometer, it was 1.390 at a wavelength of 500 nm. The absorption of the film in the visible region was 1% or less. This film has the same optical performance as a MgF ₂ single-layer antireflection film formed by ordinary vacuum deposition.

[0015]

[Embodiment 4] FIG. 4 is a graph showing the spectral characteristics of an antireflection film having a five-layer structure formed in this embodiment. A glass substrate with a refractive index of 1.6 is set in a vacuum chamber and 1 × 10 ^-3 P
After exhausting to a, CCl _{4 with} a partial pressure of 1 × 10 ⁻¹ Pa,
CF _{4 at} 1 × 10 ⁻¹ Pa and Ar at 5 × 10 ⁻² Pa were introduced into the vacuum chamber through the MFC. No substrate heating,
The target is Mg, and the optical film thickness is 45 nm while monitoring the film thickness of MgF ₂ by an optical film thickness meter by DC or RF sputtering method with an input power of 200 W.
The first layer was formed until

Then, the O 2 having a partial pressure of 2 × 10 ^-1 Pa is placed in the vacuum chamber.
₂ and 5 × 10 ⁻¹ Pa of Ar was introduced through MFC, the substrate was not heated, Zr was used as a target, and DC or RF sputtering method with an input power of 200 W was used to form ZrO ₂ by an optical film thickness meter. While monitoring the thickness, the second layer was formed until the optical film thickness reached 40 nm. Hereinafter, similarly, MgF ₂ and ZrO ₂ are each formed under the above film forming conditions, and the third layer is made of MgF ₂ with an optical film thickness of 55 n.
The fourth layer was formed of ZrO ₂ having an optical film thickness of 270 nm, and the fifth layer was formed of MgF ₂ having an optical film thickness of 126 nm.

[0017]

As described above, according to the method for producing an optical film of the present invention, Al or Mg is used as a target, and a gas containing chlorine, a gas containing fluorine and an inert gas are used as process gases. An optical film having a low refractive index without absorption can be provided by forming a film using the sputtering method.

[Brief description of drawings]

FIG. 1 is a graph showing Example 1.

FIG. 2 is a graph showing Example 2.

FIG. 3 is a graph showing Example 3.

FIG. 4 is a graph showing Example 4.

Front page continued (72) Inventor Nobuaki Mitamura 2-43-2 Hatagaya, Shibuya-ku, Tokyo Olympus Optical Co., Ltd. (72) Inventor Issei Tokuda 2-43-2 Hatagaya, Shibuya-ku, Tokyo Olympus Optical Industry Co., Ltd. (72) Inventor Bunji Akimoto 2-43-2 Hatagaya, Shibuya-ku, Tokyo Olympus Optical Industry Co., Ltd. (72) Inventor Yoshiki Nitta 2-43-2 Hatagaya, Shibuya-ku, Tokyo Olympus Optical Co., Ltd. (72) Inventor Nobuyoshi Toyohara 2-34-2 Hatagaya, Shibuya-ku, Tokyo Olympus Optical Co., Ltd.

Claims (1)

[Claims] 1. A sputtering method using aluminum or magnesium as a target material and a gas containing chlorine, a gas containing fluorine and an inert gas as a process gas to form AlF ₃ or MgF ₂ as a film. Method for manufacturing optical film.