JPH07120602A - Infrared antireflection film forming method - Google Patents

Abstract

PURPOSE:To provide a method for forming an infrared antireflection film excellent in optical characteristic, durability and adhesion to a silicon substrate by applying a specific dilute nitric acid solution or dilute hydrochloric acid solution to the surface of the silicon substrate to form a reformed layer of silicon, and then forming a zinc sulfide layer while irradiating the silicon substrate with electron beams. CONSTITUTION:An oxidized layer on the outermost surface of a silicon substrate 11 is removed by applying a dilute nitric acid solution or a dilute hydrochloric acid solution of 0.1-20wt.% to the surface of the silicon substrate 11. Partial silicon-oxygen bonding is ruptured to the depth of several tens of Angstrom angstroms in the surface oxidized layer after removal to form a reformed layer 12. At the time of forming a zinc sulfide layer 13 on this reformed layer 12, the zinc sulfide layer 13 is formed while irradiating the silicon substrate 11 with electron beams so as to be able to obtain a fine zinc sulfide film, thereby obtaining the infrared antireflection film excellent in durability and adhesion to the silicon substrate 11.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an antireflection film for optical parts, and more particularly to a method for forming an infrared antireflection film on a silicon substrate used as an infrared optical material.

[0002]

2. Description of the Related Art Silicon (Si) has been well known as an infrared optical material. However, the refractive index of silicon is higher than that of ordinary optical glass (about 3.
Therefore, the reflection is high (about 30% on one side), and an antireflection film is indispensable for use as an optical component.

A conventional infrared antireflection film for a silicon substrate and a method for forming the same will be described below with reference to the drawings. Zinc sulfide (ZnS) as a single-layer antireflection film
Is generally composed of a cross-section structure (Fig. 5)
Shown in. In FIG. 5, 51 is a silicon substrate and 52 is a zinc sulfide layer. The optical thickness of the antireflection film is λ 0/4 (λ
0 is the central wavelength of the antireflection wavelength region) and is usually formed by a vacuum vapor deposition method. Since the single-layer antireflection film composed of the zinc sulfide layer 52 has low adhesion and moisture resistance to the substrate 51, the silicon substrate 51 is heated during vapor deposition or the silicon substrate 51 is vapor deposited before vapor deposition in order to improve them. Ion bombardment is performed. In addition, the antireflection film may be multi-layered. For example, regarding the two-layer antireflection film, it is proposed that the first layer is a titanium oxide layer and the second layer is a zinc sulfide, counted from the substrate side. (For example, JP-A-56-106202)

[0004]

As described above, zinc sulfide (ZnS) is often used as the material for the antireflection coating for infrared rays. This zinc sulfide (ZnS) evaporates by sublimation when heated above 1000 ° C. However, a thin film can be formed relatively easily. However, the ZnS film deposited on the substrate surface at room temperature has a weak adhesive force and is weak against humidity. In order to solve this, a method of heating the substrate temperature to about 150 ° C. and performing vapor deposition is adopted, but this method is effective to some extent for a relatively thin film for visible region (up to about 0.2 μm). However, the film thickness is 1 as an antireflection film in the infrared region.
If the thickness is around μm, the effect of adhesion and moisture resistance is small, and cracks may occur in the film, so the effect of improvement is small. Also, the effect of improving the ion bombardment is small. Furthermore, the two-layer antireflection film consisting of a titanium oxide layer and a zinc sulfide layer improves the moisture resistance of ZnS, but this is also equivalent to a relatively thin film thickness in the near infrared region. The adhesion between the titanium oxide layer and the silicon substrate in the prevention film is also not excellent.

As described above, the conventional infrared antireflection film has
There were problems such as poor adhesion with a silicon substrate, poor moisture resistance, and lack of stability in optical characteristics. The present invention has been made in consideration of the above conventional problems, and an object of the present invention is to provide a method for forming an infrared antireflection film having excellent adhesion to a silicon substrate, durability, and optical characteristics.

[0006]

In order to solve the above-mentioned problems, the present invention provides a surface of a silicon substrate in an amount of 0.1 to 20 wt%.
Infrared reflection is prevented by applying a dilute nitric acid solution or dilute hydrochloric acid solution to form a modified layer of silicon obtained by this, and then forming a layer of zinc sulfide while irradiating the silicon substrate with an electron beam. A method for forming a film is used.

Further, 0.1 to 20 w is formed on the surface of the silicon substrate.
A dilute nitric acid solution or dilute hydrochloric acid solution of t% is applied, a modified layer of silicon obtained by this is formed, and then a dielectric layer is formed thereon, and then an electron beam is applied to the silicon substrate. However, a method of forming an infrared antireflection film by forming a layer of zinc sulfide is used.

Further, 0.1 to 20 w is formed on the surface of the silicon substrate.
A t% dilute nitric acid solution or dilute hydrochloric acid solution is applied to form a modified layer of silicon obtained by this, and then a dielectric layer is formed thereon while irradiating an ion beam, and thereafter,
A method of forming an infrared antireflection film by forming a layer of zinc sulfide while irradiating a silicon substrate with an electron beam.

[0009]

The infrared antireflection film obtained by the above method has the following functions. The structure of the formed infrared antireflection film is 2
Although it has a three-layer structure or a three-layer structure, the first layer counting from the substrate side is a modified layer of silicon obtained by applying 0.1 to 20 wt% diluted nitric acid solution or diluted hydrochloric acid solution to the surface of the silicon substrate. The material of the antireflection film can be formed thereon with good adhesion. It is removed by applying 0.1-20 wt% dilute nitric acid solution or dilute hydrochloric acid solution on the surface of the silicon substrate, and (1) first etching the oxide layer on the outermost surface of the silicon substrate.
(2) Dozens of Å (angstrom-
Part of the silicon-oxygen bonds are broken at the depth of (b) to form an activated layer (modified layer).

It has been found that when a zinc sulfide or a dielectric layer is formed on the modified layer, a film having excellent adhesion is formed. Also, when forming a zinc sulfide layer on the modified layer, a dense zinc sulfide film can be obtained by forming a zinc sulfide layer while irradiating the silicon substrate with an electron beam, and adhesion and durability to the substrate can be obtained. It is possible to obtain an excellent infrared antireflection film.

Further, by forming a dielectric layer on the modified layer and then forming a zinc sulfide layer while irradiating the silicon substrate with an electron beam, a dense zinc sulfide film can be obtained, and the adhesion to the substrate is improved. Also, an infrared antireflection film having excellent durability can be obtained.

Further, when the dielectric layer is formed on the modified layer, the dielectric layer is vapor-deposited while being irradiated with an ion beam to form a dense dielectric layer in which internal stress is relaxed. When forming the zinc sulfide layer on the dielectric layer, a dense zinc sulfide film can be obtained by forming the zinc sulfide layer while irradiating the silicon substrate with the electron beam.
It is possible to obtain an infrared antireflection film having excellent adhesion to a substrate and durability.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. (Embodiment 1) FIG. 1 shows the structure (cross-sectional view) of an infrared antireflection film according to a first embodiment of the present invention. In FIG. 1, 11 is a silicon (Si) substrate, 12 is a silicon reforming layer formed by reforming the silicon substrate 11, and 13 is a zinc sulfide layer.

The conditions for forming each layer are as follows. The silicon modified layer 12 was formed to a thickness of about 50 Å by applying a 0.1 to 20 wt% dilute nitric acid solution or dilute hydrochloric acid solution on the surface of the silicon substrate 11. Next, the zinc sulfide layer 13 is formed to have an optical thickness of λ / 4 (λ = 7000 nm) at a deposition rate of about 6 to 8Å / sec, and an electron beam is applied to the silicon substrate 11 at a current density of 4 to 6 μA / cm 2. It was formed while irradiating. FIG. 4 shows the spectral reflection characteristics (per surface) of Example 1.
Is indicated by the curve a. For comparison, the characteristics without the antireflection film are shown in (d). As can be seen from the figure, the central wavelength (λ
= 7000 nm), the reflectance was 5% or less, and excellent characteristics as an infrared antireflection film were obtained. The following items were tested in order to confirm the adhesion and durability of the antireflection film obtained by this method. (A) Peeling test (high temperature of 40 ° C, relative humidity of 85%
After standing in a high humidity atmosphere for 168 hours, the adhesive tape is adhered to the surface of the optical component and peeled off. (B) High temperature test (leave in atmosphere of temperature 80 ° C. for 250 hours) (c) Low temperature test (leave in atmosphere of temperature −20 ° C. for 250 hours) (d) Humidity resistance test (temperature 60 ° C., High temperature of 90% relative humidity
Leave in a high humidity atmosphere for 168 hours. (E) Thermal shock test (remaining in a low-temperature / high-temperature atmosphere at temperatures of -30 ° C and 80 ° C for 30 minutes alternately for about 24 hours) (f) Hydrogen sulfide gas test (hydrogen sulfide concentration 3 ppm, 40
Leave for 24 hours in the atmosphere of ° C. ) (G) Sulfurous acid gas test (sulfurous acid gas concentration 10 ppm, 4
Leave in an atmosphere of 0 ° C. for 24 hours. ) The results of the above reliability test are shown in (Table 1).

[0015]

[Table 1]

As can be seen from (Table 1), the infrared antireflection film according to this example is excellent in adhesion to the substrate and durability. (Embodiment 2) FIG. 2 shows a structure (cross-sectional view) of an infrared antireflection film according to a second embodiment of the present invention. In FIG. 2, 21 is a silicon substrate, 22 is a silicon modified layer, and 23 is a titanium dioxide layer.

The conditions for forming each layer are as follows. The formation of the silicon modified layer 22 is similar to that of the first embodiment, and the silicon modified layer 22 is formed on the surface of the silicon substrate 21 to a thickness of about 50 Å.
Was formed. Next, the titanium dioxide layer 23 is formed with an optical film thickness λ /
4 (λ = 5000nm) thickness vapor deposition rate about 4-5Å /
It was formed in sec. When the titanium dioxide layer 23 is formed, an argon ion beam is applied to the silicon substrate 21 at an accelerating voltage of 0.5.
It was formed by irradiation with kV and an ion current density of 10 to 20 .mu.A / cm @ 2. Spectral reflection characteristics of Example 2 (per surface)
Is shown by the curve b in FIG. Center wavelength (λ = 5000
nm), the reflectance was 5% or less, and excellent characteristics as an infrared antireflection film were obtained. The following items were tested in order to confirm the adhesion and durability in this example. (A) Peeling test (high temperature of 40 ° C, relative humidity of 85%
After leaving in a high humidity atmosphere for 500 hours, the adhesive tape is adhered to the surface of the optical component and peeled off. (B) High temperature test (leaving in an atmosphere of temperature 80 ° C. for 500 hours) (c) Low temperature test (leaving in an atmosphere of temperature −20 ° C. for 500 hours) (d) Moisture resistance test (temperature 60 ° C., High temperature of 90% relative humidity
Leave for 500 hours in a high humidity atmosphere. (E) Thermal shock test (remaining in low temperature / high temperature atmosphere of temperature −30 ° C., 80 ° C. for 30 minutes alternately for about 96 hours) (f) Hydrogen sulfide gas test (hydrogen sulfide concentration 3 ppm, 40
Leave for 96 hours in the atmosphere of ° C. ) (G) Sulfurous acid gas test (sulfurous acid gas concentration 10 ppm, 4
Leave in an atmosphere of 0 ° C. for 96 hours. ) The results of the above reliability test are shown in (Table 2).

[0018]

[Table 2]

As can be seen from (Table 2), the infrared antireflection film according to this example is excellent in adhesion to the substrate and durability. (Embodiment 3) FIG. 3 shows the structure (cross-sectional view) of an infrared antireflection film according to a third embodiment of the present invention. In FIG. 3, 31 is a silicon substrate, 32 is a silicon modified layer, 33 is a titanium dioxide layer, and 34 is a zinc sulfide layer.

The conditions for forming each layer are as follows. The formation of the silicon modified layer was the same as in Example 1, and the silicon modified layer 32 was formed on the surface of the silicon substrate 31 to a thickness of about 50Å. Next, the titanium dioxide layer 33 is formed with an optical film thickness of about 200.
It was formed to a thickness of Å at a vapor deposition rate of about 4 to 5 Å / sec. Next, a zinc sulfide layer 34 was formed at a vapor deposition rate of about 6 to 8 Å / sec so that the optical film thickness including the titanium dioxide layer 33 was λ / 4 (λ = 6000 nm). The titanium dioxide layer 33 is formed while irradiating the silicon substrate 31 with an argon ion beam under the same conditions as in the second embodiment, and the zinc sulfide layer (thin film) is formed under the same conditions as in the first embodiment. It was formed while irradiating the silicon substrate with the beam. Spectral reflection characteristics (per surface) of Example 3 are shown by a curve c in FIG. Center wavelength (λ = 6000n
In m), the reflectance was 5% or less, and excellent characteristics as an infrared antireflection film were obtained. The following tests were conducted to confirm the adhesion and durability of this example. (A) Peeling test (high temperature of 40 ° C, relative humidity of 85%
After leaving in a high humidity atmosphere for 250 hours, the adhesive tape is adhered to the surface of the optical component and peeled off. (B) High temperature test (leave in atmosphere of temperature 80 ° C. for 250 hours) (c) Low temperature test (leave in atmosphere of temperature −20 ° C. for 250 hours) (d) Humidity resistance test (temperature 60 ° C., High temperature of 90% relative humidity
Leave in a high humidity atmosphere for 168 hours. (E) Thermal shock test (remaining in a low temperature / high temperature atmosphere at temperatures of -30 ° C. and 80 ° C. for 30 minutes alternately for about 24 hours) (f) Hydrogen sulfide gas test (hydrogen sulfide concentration 3 ppm, 40
Leave for 24 hours in the atmosphere of ° C. ) (G) Sulfurous acid gas test (sulfurous acid gas concentration 10 ppm, 4
Leave in an atmosphere of 0 ° C. for 24 hours. ) The results of the above reliability test are shown in (Table 3).

[0021]

[Table 3]

As can be seen from (Table 3), the infrared antireflection film according to this example has excellent adhesion to the substrate and durability. By providing the titanium dioxide layer between the silicon modified layer and the zinc sulfide layer, the adhesion to the substrate was improved as compared with Example 1. Further, in this wavelength region, zinc sulfide and titanium dioxide have almost the same refractive index, and if the film thickness is about 100Å, the absorption of titanium dioxide can be ignored up to a wavelength of about 1100 nm (11 μm). Although titanium dioxide was used as the dielectric in the above-mentioned examples, zirconium dioxide, lead oxide, tantalum oxide, yttrium oxide, zirconium titanate, cerium oxide, lead telluride, etc. can also be used. Further, by providing a dielectric layer between the silicon modified layer and the zinc sulfide layer, the adhesion with the substrate can be improved.

[0023]

As is apparent from the above description of the embodiments, according to the present invention, a layer consisting of a silicon modified layer and a zinc sulfide layer is formed on the surface of a silicon substrate to form an infrared antireflection film. It is possible to realize an infrared antireflection film having excellent adhesion to and durability. Further, if it is transparent in the used wavelength range, the dielectric can be used in place of zinc sulfide. The silicon modified layer is 0.1-2 on the surface of the silicon substrate.
It can be formed by applying 0 wt% dilute nitric acid solution or dilute hydrochloric acid solution. Since it is formed while irradiating the substrate with an electron beam when forming the zinc sulfide layer, it is formed while irradiating with an ion beam when forming the dielectric layer. As a result, a dense film can be obtained.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing the structure of an antireflection film of Example 1 of the present invention.

FIG. 2 is a cross-sectional view showing the structure of an antireflection film of Example 2 of the present invention.

FIG. 3 is a sectional view showing the structure of an antireflection film of Example 3 of the present invention.

FIG. 4 is an optical characteristic diagram of an example of the present invention.

FIG. 5 is a configuration diagram of a conventional infrared antireflection film.

[Explanation of symbols]

 11 Silicon Substrate 12 Silicon Modified Layer 13 Zinc Sulfide Layer

Claims (5)

[Claims] 1. A method for forming an infrared antireflection film, which comprises forming a modified layer on the surface of a silicon substrate with an acidic solution, and then forming a zinc sulfide layer while irradiating the silicon substrate with an electron beam. 2. A modified layer is formed on the surface of a silicon substrate by an acidic solution, and then a dielectric layer is formed thereon, and then a layer of zinc sulfide is formed while irradiating the silicon substrate with an electron beam. A method for forming an infrared antireflection film. 3. A modified layer is formed on the surface of a silicon substrate with an acidic solution, and then a dielectric layer is formed thereon by irradiating an ion beam, and thereafter, the silicon substrate is irradiated with an electron beam. While forming a layer of zinc sulfide, a method for forming an infrared antireflection film. 4. The infrared reflection according to claim 1, wherein the acidic solution is a 0.1-20 wt% dilute nitric acid solution or a 0.1-20 wt% dilute hydrochloric acid solution. Method of forming a protective film. 5. The dielectric material is zirconium dioxide, lead oxide,
Tantalum oxide, yttrium oxide, zircon titanate,
The method for forming an infrared antireflection film according to claim 2 or 3, which is either cerium oxide or lead telluride.