JPH06230202A - Formation of thin film - Google Patents

Abstract

PURPOSE:To obtain a ZnS film not causing cracking, having high adhesive strength to an optical substrate and hard to scratch by forming a thin ZnS film on the surface of the optical substrate while irradiating the substrate with electron beams. CONSTITUTION:An Si substrate as an optical substrate transmitting IR is held by a substrate holder 3 so that it, confronts an evaporating source 2 and an electron gun 4 in a vacuum deposition vessel 1. This vessel 1 is evacuated and a ZnS film is formed on the unheated substrate fitted to the holder 3 in a prescribed optical thickness by depositing ZnS evaporated from the evaporating source 2 on the substrate at the prescribed rate of deposition while irradiating the substrate with electron beams from the electron gun 4. Since ZnS is irradiated with electron beams during film formation, internal stress is relaxed like the case of ion beam assisted deposition, cracking is inhibited and adhesive strength is enhanced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming an antireflection film for an infrared optical component used in, for example, an infrared detector.

[0002]

2. Description of the Related Art Germanium (Ge) and silicon (Si) are conventionally known as infrared optical materials, and their refractive indexes are Ge: n = 4.0 and Si: n = 3.0, respectively.
It is 4 (n: refractive index), and the reflection of the substrate itself is 17% and 31% per one side, respectively, and the reflection is extremely large. Therefore, when used as an optical component, antireflection is necessary.

In particular, as the antireflection film used for these, a single-layer antireflection film made of ZnS, a two-layer antireflection film made of ZnS, magnesium fluoride (MgF ₂ ) and the like are known. ZnS is one of the particularly useful optical materials because it is transparent in the infrared region up to about 25 μm, has a high refractive index, and can be deposited easily.

Among these, a conventional ZnS single-layer antireflection film is used as an example for a Si substrate, and a conventional Zn
The antireflection film of S and its forming method will be described.

[0005] The anti-reflection film 7 of ZnS on the surface of FIG. 2 is Si substrate 6 nd = λ _0/4 cross section when formed in a thickness of (nd:: optical thickness, lambda ₀ the center wavelength of the antireflection film) It is a figure. The ZnS antireflection film 7 is usually formed by a vacuum vapor deposition method using, for example, the vapor deposition apparatus shown in FIG. The vapor deposition vapor supplied from the evaporation source 2 forms a thin film on the substrate held by the holder 3. Reference numeral 5 is a heater for heating the substrate. Zn deposited on the substrate side at room temperature
The S film has weak adhesion and is easily scratched. However, it is well known as a general technique that if a substrate is heated to about 150 ° C. by a heater 5 and further subjected to glow discharge treatment within 5 minutes immediately before vapor deposition, a film with strong adhesion and scratch resistance is obtained ( For example, "Vacuum deposition" 9-3-1 ZnS, Tsuyoshi Sawaki, Nikkan Kogyo Shimbun).

[0006]

However, ZnS
Is a substance with a large internal stress, and even if the antireflection film is formed by the above method, if the film thickness is increased in accordance with a long wavelength region such as far infrared rays, there is a drawback that cracks are likely to occur after formation. It is hard to say that it is excellent in mass productivity. For this reason, recently, the inert gas ions generated by the ion source are accelerated to several hundreds to several kV and irradiated to the film being formed (hereinafter referred to as ion beam assist) to relax the internal stress of the film, At the same time, methods have been proposed for obtaining various properties that cannot be obtained by conventional methods, such as increasing packing density and improving adhesion. However, even with this method, the crystallinity of the ZnS film is rather improved and cracks occur.

In view of the above problems, the present invention aims to provide a method for forming a ZnS film which does not generate cracks and has a strong adhesive force and is not easily scratched.

[0008]

In order to achieve the above object, in the present invention, when a vapor deposition film made of ZnS is vapor-deposited on an optical material by vacuum vapor deposition, the film is irradiated with an electron beam and a thin film is formed. To form.

[0009]

The present invention can improve the crack resistance, adhesion and durability of the ZnS film by the method of forming a thin film having the above-mentioned structure.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below based on embodiments with reference to the drawings.

FIG. 1 shows a thin film forming apparatus equipped with an embodiment of the thin film forming method of the present invention, and a state at the time of forming an antireflection film in the apparatus. The optical substrate 6 is held by the substrate holder so as to face the evaporation source 2 and the electron gun 4.

The apparatus of the embodiment is intended to obtain an optical component whose cross-sectional view is shown in FIG. In FIG. 2, the substrate 6, which is an optical base, is Si, and 7 is a ZnS film.

The conditions for forming the ZnS film are as follows. After evacuating the inside of the vacuum deposition tank 1 to 2.0 × 10 ⁻⁵ Torr, the unheated substrate attached to the substrate holder 3 is irradiated with the electron beam from the electron gun 4 and evaporated from the evaporation source 2. the come ZnS, optical thickness _{nd = λ 0/4 (λ} 0 = 1
A thickness of 0 μm) was formed on the substrate at a vapor deposition rate of about 8 to 11 Å / sec.

By irradiating ZnS with an electron beam during formation, similar to the ion beam assist, internal stress is relaxed, cracks are suppressed, and the adhesion is improved. However, the crystallinity of ZnS, which is a drawback of performing ion beam assist, does not become too good.

The tests carried out to confirm the adhesion and durability of the antireflection film of the above-mentioned examples are as follows: (1) Adhesive tape peeling test (temperature 40 ° C., relative humidity 85
%, After leaving it in a high temperature / high humidity atmosphere for 1000 hours, adhere the adhesive tape to the surface of the optical component and peel it off. (2) Humidity test (temperature 40 ° C, relative humidity 95% high temperature /
It is left in a high humidity atmosphere for 1000 hours. (3) Thermal shock test (temperatures of -40 ° C. and 120 ° C. in a low temperature / high temperature atmosphere alternately for 30 minutes each for about 100 hours).

[0016]

[Table 1]

As can be seen from Table 1, the antireflection film of this example is excellent in adhesion and durability.

[0018]

As is apparent from the above description, the antireflection film of the optical component of the present invention has the following properties when the vapor deposition film made of ZnS is vapor-deposited to a desired thickness on the surface of the optical material: By forming a film while irradiating the film with an electron beam, it has the effect of preventing cracks from occurring, the adhesion force,
It is possible to improve the moisture resistance.

[Brief description of drawings]

FIG. 1 is a sectional view of a vapor deposition apparatus embodying an embodiment of a thin film forming method of the present invention.

FIG. 2 is a sectional view of an optical component formed by the apparatus of the embodiment.

FIG. 3 is a sectional configuration diagram of a conventional vapor deposition device.

[Explanation of symbols]

 1 Vacuum Deposition Tank 2 Evaporation Source 3 Substrate Holder 4 Electron Gun 5 Heater 6 Substrate 7 Zinc Sulfide (ZnS) Film

Claims (1)

[Claims] 1. When forming an antireflection film made of zinc sulfide (ZnS) on the surface of an optical base material transparent to infrared light, ZnS is irradiated onto the optical base material while irradiating an electron beam.
Forming a thin film.