JP3361621B2 - Anti-reflection coating for infrared region - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an infrared antireflection film.

[0002]

2. Description of the Related Art Recently, optical devices using infrared rays have been actively used, for example, for nighttime monitoring and temperature measurement. With the expansion of this application, the development of a high-performance antireflection coating for the infrared region has been demanded. By the way, the refractive index of the lens material and the window material which are the substrate of the antireflection film for infrared region is quite high. A single material having a high refractive index causes a large loss of reflection and cannot be used as it is. Especially, Ge having a refractive index of 4 and Si having a refractive index of 3.4 are often used as a lens material in the infrared region.
As the performance of optical equipment has improved, Te with a refractive index of 5 and GaAs with a refractive index of 3.3 and Ge, Si, As, S
Chalcogenide glass having a refractive index of 3 or more obtained by blending e, Te and the like has also been applied as a material for lenses and windows. Therefore, it is becoming more important how to coat the substrate material having a high refractive index with the antireflection film.

Conventionally, the simplest method of forming these antireflection films is ns ^{1/2 where} the refractive index of the substrate is ns.
There is a method in which a film having a refractive index of 1 is coated on the substrate with an optical film thickness (= refractive index x film thickness) of about 1/4 of the wavelength to be transmitted. Here, the wavelength to be transmitted in the infrared ray is a band called "atmosphere window" in which water vapor is not absorbed and light rays can be transmitted to a long distance.
.About.5 .mu.m, 8 to 12 .mu.m, and the optical film thickness is usually adjusted to about 1/4 of any of the central wavelengths of 2.25 .mu.m, 4 .mu.m and 10 .mu.m. However, while the antireflection film made of this single-layer film (one-layer film) can be easily manufactured, the antireflection effect over the entire band cannot be expected.

As a solution to these problems, at present, an antireflection property over the entire band is provided by a multilayer antireflection film. For example, as disclosed in JP-A-64-15703, JP-A-2-135401, JP-B-2-11121, and JP-B2-137761, a ZnS layer, a Ge layer, and a It is known to form four layers of a ZnS layer and a metal fluoride layer, and to partially improve this. In Japanese Patent Publication No. 2-11121, ZnS is further laminated on the metal fluoride which is the outermost layer of the above structure, but this is an improvement for protecting the metal fluoride having poor durability. Is.

Further, Japanese Patent Laid-Open No. 4-221901 discloses
SiO ₂ is arranged on the first layer closest to the substrate, and Ge and Z are sequentially arranged.
A four-layer film of nS and metal fluoride is formed. Furthermore, as another example of the antireflection film in the infrared region, Japanese Patent Laid-Open No.
Japanese Patent No. 136901 discloses an antireflection film including four layers of a metal fluoride layer, a Si or Ge layer, a metal fluoride layer, and a MgF ₂ or CaF ₂ layer in this order from the substrate.

[0006]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
In the case of technology such as Japanese Patent Laid-Open No. 703, Japanese Patent Laid-Open No. 4-221
As already pointed out in Japanese Patent No. 901, for example, ZnS of the technology has poor adhesion to the substrate, and therefore the film structure of the technology has a difficulty in durability. Further, in the case of the technique disclosed in Japanese Patent Laid-Open No. 4-221901, a wavelength of about 2
The absorption of the SiO ₂ layer for infrared light at ˜3 μm is a problem. This absorption is absorption of H ₂ O contained in SiO ₂ , and the occurrence of this absorption is unavoidable in the electron beam evaporation method and the sputtering method which are commonly used film forming methods, and it is high as an antireflection film including this region. Characteristics cannot be expected. Further, in the technique of the above-mentioned Japanese Patent Laid-Open No. 4-136901, the metal fluoride is multi-layered, but in order to form the metal fluoride into a dense film, it is necessary to elevate the substrate temperature for vapor deposition.
Generally, in this case, the tensile stress generated inside the film becomes high, and when three layers of metal fluoride are laminated in this way, there is a problem that durability such as cracks is lacking.

That is, the present invention has been made to solve the above problems, and an object thereof is to provide an antireflection film having excellent antireflection properties and durability.

[0008]

In the infrared antireflection film of the present invention, the substrate is selected from Ge, Si, GaAs and Te.
One type of chalcogenide glass with a refractive index of 3 or more
Is provided on the substrate, and Al ₂ O ₃ is provided in order from the substrate side.
Layer, Ge layer, ZnS layer, consisting of four layers of metal fluoride layer
An infrared antireflection film, wherein the metal fluoride is Mg
F ₂ , CeF ₃ , YF ₃ , ThF ₄ , CaF ₂ and Cry
It is an infrared antireflection film characterized by being a kind selected from olite (Na ₃ AlF ₆ ) .

[0009]

[0010]

[0011]

When the substrate is Ge, the range of the optical film thickness of each layer is 45 to 1 for the Al ₂ O ₃ layer.
80 nm, 180 to 570 nm for Ge layer, Zn
The antireflection film having an S layer of 400 to 1300 nm and a metal fluoride layer of 640 to 1160 nm is preferable.

When the substrate is made of Ge, the range of the optical film thickness of each layer is set to 35 to 35 for the Al ₂ O ₃ layer.
90 nm, 135-300 nm for Ge layer, Zn
The antireflection film having an S layer of 300 to 800 nm and a metal fluoride layer of 350 to 700 nm is preferable.

When the substrate is made of Ge, the range of the optical film thickness of each layer is 60 to 60 for the Al ₂ O ₃ layer.
105 nm, 270-380 nm for Ge layer, Z
The antireflection film having an nS layer thickness of 710 to 820 nm and a metal fluoride layer thickness of 630 to 800 nm is preferable.

When the substrate is Si, the range of the optical film thickness of each layer is 55 to 22 for the Al ₂ O ₃ layer.
0 nm, 100-470 nm for Ge layer, ZnS
The antireflection film having a layer of 380 to 1380 nm and a metal fluoride layer of 615 to 1170 nm is preferable.

When the substrate is made of Si, the range of the optical film thickness of each layer is 40 to 40 for the Al ₂ O ₃ layer.
130 nm, 90-230 nm for Ge layer, Zn
The antireflection film having an S layer of 200 to 870 nm and a metal fluoride layer of 390 to 680 nm is preferable.

When the substrate is made of Si, the range of the optical film thickness of each layer is 80 to 80 for the Al ₂ O ₃ layer.
120 nm, 220-280 nm for the Ge layer, Z
The antireflection film having an ns layer of 760 to 870 nm and a metal fluoride layer of 720 to 790 nm is preferable.

Further, when the substrate is GaAs, the range of the optical film thickness of each layer is 65% for the Al ₂ O ₃ layer.
210 nm, 110-440 nm for the Ge layer, Z
The antireflection film having an nS layer thickness of 480 to 1300 nm and a metal fluoride layer thickness of 810 to 1130 nm is preferable.

When the substrate is GaAs, the optical film thickness of each layer is 40 to 140 nm for the Al ₂ O ₃ layer and 80 to 230 n for the Ge layer.
The antireflection film having a thickness of 180 to 840 nm for the ZnS layer and 400 to 675 nm for the metal fluoride layer is preferable.

When the substrate is made of GaAs, the range of the optical film thickness of each layer is 85 to 125 nm for the Al ₂ O ₃ layer and 210 to 270 n for the Ge layer.
The antireflection film having a thickness of 770 to 875 nm for the ZnS layer and a metal fluoride layer of 710 to 785 nm is preferable.

When the substrate is Te, the range of the optical film thickness of each layer is 25 to 14 for the Al ₂ O ₃ layer.
0 nm, 300 to 950 nm for Ge layer, ZnS
The antireflection film having a thickness of 470 to 1200 nm and a metal fluoride layer of 750 to 1200 nm is preferable.

[0022]

In the infrared antireflection film of the present invention, since the antireflection film has four layers of Al ₂ O ₃ layer, Ge layer, ZnS layer and metal fluoride layer arranged in this order from the substrate side, Al ₂ O
Not only the durability is improved by the strong adhesive force of No. ₃ , but also by appropriately adjusting the film thickness, a substrate having a refractive index of 3 or more can have a high transmittance regardless of the refractive index of the substrate.

In addition, MgF ₂ , CeF ₃ , YF ₃ and Th
Since F ₄ , CaF ₂ and cryolite (Na ₃ AlF ₆ ) have a low refractive index and excellent durability, it is possible to arrange a film having a low refractive index in the outermost layer of the multilayer film by using the metal fluoride. Therefore, an antireflection film for infrared region having a high transmittance and a high durability can be obtained.

Further, since Ge, Si, GaAs and Te have high infrared light transmissivity, when they are used as a substrate, an optical component having high transmissivity can be obtained.

Further, since chalcogenide glass having a refractive index of 3 or more has a high infrared light transmissivity, when they are used as a substrate, an optical component having a high transmissivity can be obtained.

In the antireflection film, the substrate is made of Ge.
In that case, the range of the optical film thickness of each layer is 45 to 180 nm for the Al ₂ O ₃ layer and 180 for the Ge layer.
˜570 nm, 400-1300 n for ZnS layer
m and the metal fluoride layer were set to 640 to 1160 nm, and therefore, when the antireflection film is arranged on both surfaces of the substrate, it may have an average transmittance of 95% or more in the infrared region of 3 to 5 μm. it can.

In the antireflection film, the substrate is made of Ge.
In that case, the range of the optical film thickness of each layer is 35 to 90 nm for the Al ₂ O ₃ layer and 135 to 90 nm for the Ge layer.
300 nm, 300-800 nm for the ZnS layer,
Since the metal fluoride layer is 350 to 700 nm, when the antireflection film is arranged on both sides of the substrate, it may have an average transmittance of 97% or more in the infrared range of 2 to 2.5 μm. it can.

In the antireflection film, the substrate is Ge.
In that case, the range of the optical film thickness of each layer is 60 to 105 nm for the Al ₂ O ₃ layer and 270 for the Ge layer.
~ 380 nm, 710-820 n for the ZnS layer
m and the metal fluoride layer were set to 630 to 800 nm, so that when the antireflection film is arranged on both sides of the substrate,
It can have an average transmittance of 93% or more in the range of 2 to 5 μm in the infrared region.

In the antireflection film, the substrate is made of Si.
In that case, the range of the optical thickness of each layer is 55 to 220 nm for the Al ₂ O ₃ layer and 100 for the Ge layer.
~ 470 nm, 380-1380 n for ZnS layer
Since m and the metal fluoride layer are 615 to 1170 nm, when the antireflection film is arranged on both surfaces of the substrate, it may have an average transmittance of 95% or more in the infrared region of 3 to 5 μm. it can.

In the antireflection film, the substrate is made of Si.
In that case, the range of the optical film thickness of each layer is 40 to 130 nm for the Al ₂ O ₃ layer and 90 to 90 nm for the Ge layer.
230 nm, 200-870 nm for the ZnS layer,
Since the metal fluoride layer has a thickness of 390 to 680 nm, when the antireflection film is arranged on both sides of the substrate, it may have an average transmittance of 95% or more in the infrared range of 2 to 2.5 μm. it can.

In the antireflection film, the substrate is made of Si.
In that case, the range of the optical film thickness of each layer is 80 to 120 nm for the Al ₂ O ₃ layer and 220 for the Ge layer.
~ 280 nm, 760-870 n for ZnS layer
m and the metal fluoride layer were set to 720 to 790 nm, so that when the antireflection film is arranged on both sides of the substrate,
It can have an average transmittance of 93% or more in the range of 2 to 5 μm in the infrared region.

In the antireflection film, the substrate is made of Ga.
The range of the optical thickness of each layer in the case of the As, _Al 2 O
65-210 nm for ₃ layers, 1 for Ge layer
10-440 nm, 480-130 for ZnS layer
0 nm, 810 to 1130 n for metal fluoride layer
Therefore, when the antireflection film is provided on both sides of the substrate, it can have an average transmittance of 95% or more in the infrared region of 3 to 5 μm.

In the antireflection film, the substrate is made of Ga.
The range of the optical thickness of each layer in the case of the As, _Al 2 O
40-140 nm for ₃ layers and 8 for Ge layer
0-230 nm, 180-840 n for ZnS layer
m and the metal fluoride layer were set to 400 to 675 nm. Therefore, when the antireflection film is arranged on both sides of the substrate,
It can have an average transmittance of 97% or more in the infrared range of 2 to 2.5 μm.

In the antireflection film, the substrate is Ga
The range of the optical thickness of each layer in the case of the As, _Al 2 O
85-125 nm for ₃ layers and 2 for Ge layers
10 to 270 nm, 770 to 875 for the ZnS layer
nm, and the metal fluoride layer was set to 710 to 785 nm, so that when the antireflection film is arranged on both surfaces of the substrate, it may have an average transmittance of 93% or more in the infrared region of 2 to 5 μm. it can.

In the antireflection film, the substrate is made of Te.
In that case, the range of the optical thickness of each layer is 25 to 140 nm for the Al ₂ O ₃ layer and 300 for the Ge layer.
~ 950 nm, 470-1200 n for ZnS layer
m and the metal fluoride layer are set to 750 to 1200 nm, and therefore, when the antireflection film is arranged on both surfaces of the substrate, it may have an average transmittance of 95% or more in the infrared region of 3 to 5 μm. it can.

[0036]

EXAMPLES The antireflection film of the present invention will be described in detail below. FIG. 1 is a sectional explanatory view showing the structure of one embodiment of the antireflection film of the present invention.

As shown in FIG. 1, for example, the infrared antireflection film of the present invention has a lens 1 and a window 1 as a substrate 1 and an Al ₂ O ₃ layer 2, a Ge layer 3, a ZnS layer 4 in this order.
The feature is that the metal fluoride layer 5 is provided. In addition, the infrared region in the present invention means a range of 2 to 5 μm, and depending on the case, 2 to 2.5 μm and 3 to 5 μm of the window of the atmosphere.
It is divided into two ranges and handled.

Arranging Al ₂ O ₃ in the first layer from the substrate improves the antireflection property, and also improves the substrate material and Al ₂ O 3.
_{This is because} the strong adhesion of No. ₃ improves the durability of the antireflection film.

As the metal fluoride of the fourth layer, Mg
_{F 2, CeF 3, YF 3} , ThF 4, CaF 2, cryolite _{(Na 3 AlF 6), AlF} 3, LiF 2, B
Examples include metal fluorides such as aF ₂ , LaF ₃ , and NaF, but it is desirable that the fourth layer has a small refractive index, and if the durability of the outermost layer is taken into consideration, Mg
It is preferably one selected from F ₂ , CeF ₃ , YF ₃ , ThF ₄ , CaF ₂ , and cryolite.

The forms and characteristics of the materials of the first to fourth layers are not particularly limited, except that the refractive index is close to a desired value. However, since the refractive index changes depending on the film manufacturing method and the density, the refractive index of Al ₂ O ₃ of the first layer is 1.53 to 1.62, and Ge of the second layer is 3.
8 to 4.1, 2.15 to 2.3 for the ZnS of the third layer.
It is preferably 25. Regarding the metal fluoride of the fourth layer, MgF ₂ was 1.32 to 1.37, CeF
₃ and YF ₃ are 1.53 to 1.6, and ThF ₄ is 1.42.
1.54, CaF ₂ and cryolite are 1.37 to 1.
It is preferably in the range of 42. The purity is preferably 99% or more, and more preferably 99.9% or more for all materials.

The substrate 1 is used as an infrared optical component and is not limited to a flat plate, but may be a plate having a curvature, a lens, a prism, or any other predetermined shape.

The thickness of the substrate 1 is not particularly limited, but from the infrared window of about 0.1 mm to the thickness c.
There are m thick lenses and prisms, and the same antireflection effect can be imparted to these substrates.

The material of the substrate 1 is not particularly limited as long as it transmits infrared light well and has a refractive index of 3 or more. For example, Ge, Si, GaAs, Te and chalcogenide glass have transmittances. High quality materials are preferable because they are relatively inexpensive and easily available. The chalcogenide glass has a refractive index of 3.55 for Ge ₁₀ As ₂₀ Te ₇₀ , a refractive index of 3.1 for Si ₁₅ Ge ₁₀ As ₂₅ Te ₅₀ , and a refractive index of 3.0 for Ge ₃₀ As ₁₇ Te ₃₀ Se _23. A material having a refractive index of 3 or more is preferable because it can be obtained relatively easily.

These substrates are used as a single component such as a prism, or in an infrared camera, by using these two or three different materials as a lens, achromatism (aberration due to the dispersion of the refractive index of the substrate is caused). Correction).

The material of the substrate is not particularly limited as long as it can be used for infrared optics.

The optical film thickness of each layer is not particularly limited as long as it is determined so as to increase the transmittance in a desired wavelength band, but the Al ₂ O ₃ layer is 25 to 210 nm and the Ge layer is 20 nm.
˜950 nm, the ZnS layer is preferably 180 to 1380 nm, and the metal fluoride layer is preferably 350 to 1200 nm. When the antireflection film is arranged on both sides of the substrate,
It can have an average transmittance of 90% or more in the respective wavelength bands of 3 to 5 μm, 2 to 2.5 μm, and 2 to 5 μm in the infrared region. In the present invention, the substrate has a thickness of 0.1 m.
In the range of about m to several cm, the transmittance value does not depend on the thickness of the substrate.

When it is desired to impart a high transmittance to a wavelength range of 2 to 2.5 μm of the atmospheric window most used in the infrared optical equipment, 2 to 2.5 μm, 3 to 5 μm, and both of them, It is more preferable that the film thickness is.

When the substrate is Ge, the range of the optical film thickness of each layer is 45 to 180 nm, further 60 to 180 nm for the Al ₂ O ₃ layer, and 180 to 5 for the Ge layer.
70 nm, further 180 to 390 nm, and ZnS layer 400 to 1300 nm, further 400 to 860 n.
m, the metal fluoride layer is 640 to 1160 nm, and further 735 to 880 nm is 3 to 5 in the infrared region.
It is preferable in that the transmittance at μm is high, and when the antireflection film is arranged on both surfaces of the substrate, it is 3 to 5 μm in the infrared region.
The average transmittance in the range of m is 95%, preferably 97% or more.

Similarly, when the substrate is Ge, the range of the optical film thickness of each layer is 35 to 90 n for the Al ₂ O ₃ layer.
m and Ge layers are 135 to 300 nm, ZnS layers are 300 to 800 nm, and metal fluoride layers are 350 to 700 nm.
It is preferable from the viewpoint of high transmittance in μm, and when the antireflection film is provided on both surfaces of the substrate, it is preferable that the infrared rays 2 to 2
The average transmittance in the range of 5 μm is 97% or more.

Similarly, when the substrate is Ge, the range of the optical film thickness of each layer is 60 to 105 for the Al ₂ O ₃ layer.
nm, 270 to 380 nm for the Ge layer, 710 to 820 nm for the ZnS layer, and 630 to 800 nm for the metal fluoride layer.
It is preferable from the viewpoint of high transmittance at m, and when the antireflection film is arranged on both surfaces of the substrate, it is 2 to 5 μm in the infrared region.
The average transmittance in the range is 93% or more.

When the substrate is made of Si, the range of the optical film thickness of each layer is 55 to 220 for the Al ₂ O ₃ layer.
nm, further 55 to 210 nm, 10 for Ge layer
0 to 470 nm, further 100 to 257 nm, and ZnS layer, 380 to 1380 nm, further 380 to 92.
0 nm, 615 to 1170 n for the metal fluoride layer
m and further 840 to 923 nm is 3 in the infrared region.
It is preferable in that it has a high transmittance at ˜5 μm, and when the antireflection film is arranged on both sides of the substrate, it is
Average transmittance in the range of 5 μm is 95%, preferably 97%
That is all.

Similarly, when the substrate is Si, the range of the optical film thickness of each layer is 40 to 130 for the Al ₂ O ₃ layer.
nm, the Ge layer is 90 to 230 nm, the ZnS layer is 200 to 870 nm, and the metal fluoride layer is 390 to 680 nm.
It is preferable from the viewpoint of high transmittance in μm, and when the antireflection film is provided on both surfaces of the substrate, it is preferable that the infrared rays 2 to 2
The average transmittance is 95% or more in the range of 5 μm.

Similarly, when the substrate is Si, the range of the optical film thickness of each layer is 80 to 120 for the Al ₂ O ₃ layer.
nm for the Ge layer, 220 to 280 nm for the Ge layer, 760 to 870 nm for the ZnS layer, and 720 to 790 nm for the metal fluoride layer.
It is preferable from the viewpoint of high transmittance at m, and when the antireflection film is arranged on both surfaces of the substrate, it is 2 to 5 μm in the infrared region.
The average transmittance in the range is 93% or more.

Further, when the substrate is GaAs, the range of the optical film thickness of each layer is about 65 to about Al ₂ O ₃ layer.
210 nm, 110-440 nm for the Ge layer, Z
480 to 1300 nm for the nS layer and 810 to 1130 nm for the metal fluoride layer are preferable from the viewpoint of high transmittance in the infrared region of 3 to 5 μm,
When the antireflection film is provided on both surfaces of the substrate, the average transmittance in the infrared region of 3 to 5 μm is 95% or more.

When the substrate is GaAs, the range of the optical film thickness of each layer is 40 to 1 for the Al ₂ O ₃ layer.
40 nm, 80-230 nm for Ge layer, ZnS
The layer has a wavelength of 180 to 840 nm, and the metal fluoride layer has a wavelength of 400 to 675 nm.
It is preferable in that the transmittance at 2.5 μm is high, and when the antireflection film is arranged on both surfaces of the substrate, it is
The average transmittance in the range of up to 2.5 μm is 97% or more.

When the substrate is GaAs, the range of the optical film thickness of each layer is 85-1 for the Al ₂ O ₃ layer.
25 nm, 210 to 270 nm for Ge layer, Zn
The S layer has a wavelength of 770 to 875 nm, and the metal fluoride layer has a wavelength of 710 to 785 nm.
It is preferable from the viewpoint that the transmittance at 5 μm is high, and when the antireflection film is arranged on both sides of the substrate, it has a wavelength of 2 to 5 in the infrared region.
The average transmittance is 93% or more in the μm range.

Further, when the substrate is Te, the range of the optical film thickness of each layer is 25 to 14 for the Al ₂ O ₃ layer.
0 nm, 300 to 950 nm for Ge layer, ZnS
The layer has a wavelength of 470 to 1200 nm, and the metal fluoride layer has a wavelength of 750 to 1200 nm.
It is preferable in that it has a high transmittance at ˜5 μm, and when the antireflection film is arranged on both sides of the substrate, it is
The average transmittance is 95% or more in the range of 5 μm.

When the substrate is chalcogenide glass having a refractive index of 3.4 to 3.55, the range of the optical film thickness of each layer is 55 to 220 nm for the Al ₂ O ₃ layer and Ge.
100-470 nm for layers, 380-1380 nm for ZnS layers, 61 for metal fluoride layers.
It is preferably 5 to 1170 nm from the viewpoint of high transmittance in the infrared region of 3 to 5 μm, and when the antireflection film is arranged on both surfaces of the substrate, the average in the infrared region of 3 to 5 μm is obtained. The transmittance becomes 95% or more.

Similarly, when the substrate is chalcogenide glass having a refractive index of 3.4 to 3.55, the range of the optical film thickness of each layer is 40 to 130 nm for the Al ₂ O ₃ layer and Ge.
90-230 nm for layers and 2 for ZnS layers
0 to 870 nm, 390 to about the metal fluoride layer
680 nm is preferable from the viewpoint of high transmittance in the infrared region of 2 to 2.5 μm, and when the antireflection film is arranged on both surfaces of the substrate, it is in the infrared region of 2 to 2.5 μm. Has an average transmittance of 95% or more.

Similarly, when the substrate is chalcogenide glass having a refractive index of 3.4 to 3.55, the range of the optical film thickness of each layer is 80 to 120 nm for the Al ₂ O ₃ layer and Ge.
220-280 nm for layers, 760-870 nm for ZnS layers, 720 for metal fluoride layers.
˜790 nm is preferable from the viewpoint of high transmittance in the infrared region of 2 to 5 μm, and when the antireflection film is arranged on both surfaces of the substrate, the average transmission in the infrared region of 2 to 5 μm is obtained. The rate is 93% or more.

Further, when the substrate is chalcogenide glass having a refractive index of 3.3, the range of the optical film thickness of each layer is A
65 nm to 210 nm for the l ₂ O ₃ layer, 110 nm to 440 nm for the Ge layer, and 480 nm for the ZnS layer.
1300 nm, 810-11 for metal fluoride layer
30 nm is preferable from the viewpoint of high transmittance in the infrared region of 3 to 5 μm, and when the antireflection film is arranged on both surfaces of the substrate, the average transmittance in the infrared region of 3 to 5 μm is obtained. Is over 95%.

When the substrate is made of 3.3 chalcogenide glass, the range of the optical film thickness of each layer is Al ₂ O ₃
40-140 nm for layers, 80 for Ge layers
~ 230 nm, 180-840 n for the ZnS layer
m, and the metal fluoride layer is preferably 400 to 675 nm from the viewpoint of high transmittance in the infrared region of 2 to 2.5 μm, and when the antireflection film is arranged on both surfaces of the substrate, The average transmittance is 97% or more in the outer range of 2 to 2.5 μm.

When the substrate is 3.3 chalcogenide glass, the range of the optical film thickness of each layer is Al ₂ O ₃
85-125 nm for layers and 21 for Ge layers
0-270 nm, 770-875 n for ZnS layer
m, the metal fluoride layer is preferably 710 to 785 nm from the viewpoint of high transmittance in the infrared region of 2 to 5 μm, and when the antireflection film is arranged on both surfaces of the substrate, The average transmittance in the range of 2 to 5 μm is 93.
% Or more.

The antireflection film is preferably used for applications such as prisms and lenses of infrared cameras.

The method of forming the antireflection film is not particularly limited, and examples thereof include a vacuum vapor deposition method, an ion plating method, a sputtering method and a CVD method. Among them, the vacuum vapor deposition method for forming an optical multilayer film is preferable from the viewpoint of film thickness control and film thickness uniformity. The method and a vacuum vapor deposition apparatus for carrying out the method will be described below with reference to the drawings. FIG. 2 shows a cross-sectional explanatory view of an example of the vapor deposition apparatus. In FIG. 2, 6 is a vacuum container for obtaining a high vacuum, and 7 is a substrate mounting dome for mounting the substrate 1 to be vapor-deposited, which is rotated during vapor deposition to improve the uniformity of the film. Reference numeral 8 denotes a crucible for containing a vapor deposition substance, and the crucible rotating stage 9 moves the crucible 8 containing the substance to be vapor deposited to a position where the electron beam emitted from the electron gun 10 hits. The substance heated and evaporated by the electron beam is deposited on the surface of the substrate 1 to form a film. The thickness of this vapor-deposited film is measured by measuring the film thickness of the monitor glass substrate 12 with a reflective optical film thickness meter 11 mounted above the vacuum container 6, and when it reaches a desired thickness. The shutter 13 closes. Thereafter, the antireflection film of the present invention can be obtained by sequentially forming vapor-deposited films of different layers with a predetermined thickness in the same manner.

The electron beam evaporation method in each of the examples described below was performed by the above method.

Further, not only the electron beam method but also a resistance heating method in which an electric current is passed through a metal crucible to heat the vapor deposition material can be used for heating the vapor deposition material. Further, as the optical film thickness meter, not only a reflection type film thickness meter but also a transmission type optical film thickness meter in which a light source is provided below a vacuum container can be used.

Next, the infrared reflection preventing film of the present invention will be described in more detail with reference to specific examples.

[Examples 1 to 23 and Comparative Examples 1 and 2] Disc-shaped substrates made of the materials shown in Tables 1 and 2 each having a diameter of 30 mmφ and a thickness of 1 mm and polished on both sides were mounted on a substrate mounting dome of a vapor deposition apparatus. , The first layer, the second layer, the third layer, and the fourth layer having the materials and the optical film thicknesses shown in Tables 1 and 2 are stacked in this order from the substrate by the electron beam evaporation method at a vacuum degree of 1 × 10 ⁻⁴ torr or less. Then, an antireflection film for infrared region was formed.

Vapor deposition was also carried out on the opposite surface of the substrate by the same procedure to obtain substrates having infrared reflection preventing films on both surfaces.

The chalcogenide glass is Ge ₃₀
As ₁₇ Te ₃₀ Se ₂₃ (refractive index 3.0) was used.

As a durability test of the obtained substrate, a tape peeling test, a humidity resistance test and an infrared transmittance test were carried out by the following methods. The results are shown in Tables 1 and 2 and FIGS. (Tape peel test) US military standard MIL-C-48497
According to A, cellophane tape (manufactured by Nichiban Co., Ltd., width 1
2 mm) was attached to the film surface of the substrate with a length of about 10 mm, and the operation of rapidly peeling vertically was performed once, and the peeled state of the film was observed. (Humidity resistance test) The substrate was left for 24 hours in a constant temperature / humidity bath at a temperature of 50 ° C. and a relative humidity of 95 to 100%, and the film surface of the substrate was visually observed to check for stains, cloudiness, peeling, etc. . (Infrared transmittance test) Infrared spectrophotometer (JASCO Corporation)
Manufactured by IR-810) to measure the spectral transmittance curve.

[0073]

[Table 1]

[0074]

[Table 2] From the transmittance measurement results shown in FIGS. 3 to 15, in the case of the examples of the present invention, desired transmission bands (3 to 5 μm: Examples 1 to 12, 20 to 23, 2 to 2.5 μm: Example 1
3 to 16 and 2 to 5 μm: Examples 17 to 19) show high transmittance. Further, in Comparative Example 2, it is found that there is absorption near the wavelength of 3 μm and the transmittance is low.

From the results of the durability tests shown in Tables 1 and 2, no abnormalities were found in Examples 1 to 23, but in Comparative Example 1, some peeling occurred in the tape peeling test.

[0076]

EFFECTS OF THE INVENTION According to the infrared antireflection film of the present invention, since the antireflection film is formed of four layers of the Al ₂ O ₃ layer, the Ge layer, the ZnS layer and the metal fluoride layer in this order from the substrate, It has excellent prevention properties and durability.

The metal fluoride is MgF ₂ , Ce.
When it is a kind selected from F ₃ , YF ₃ , ThF ₄ , CaF ₂ and cryolite (Na ₃ AlF ₆ ),
It is possible to obtain an antireflection film for infrared region having a high transmittance and a high durability.

Further, since the substrate is a kind selected from Ge, Si, GaAs and Te, an infrared antireflection film having a high transmittance can be obtained.

When the substrate is chalcogenide glass having a refractive index of 3 or more, an infrared antireflection film having a high transmittance can be obtained.

The substrate is Ge and the optical film thickness of each layer is 45 to 180 nm for the Al ₂ O ₃ layer.
If the Ge layer has a thickness of 180 to 570 nm, the ZnS layer has a thickness of 400 to 1300 nm, and the metal fluoride layer has a thickness of 640 to 1160 nm. It has an average transmittance of 95% or more in the range of ˜5 μm.

Further, the substrate is Ge, and the optical film thickness range of each layer is 35 to 90 nm for the Al ₂ O ₃ layer and G
The e layer is 135 to 300 nm, the ZnS layer is 300 to 800 nm, and the metal fluoride layer is 35 nm.
When the antireflection film is arranged on both sides of the substrate in the case of 0 to 700 nm, the substrate has an average transmittance of 97% or more in the infrared region of 2 to 2.5 μm.

The substrate is Ge, and the optical film thickness of each layer is 60 to 105 nm for the Al ₂ O ₃ layer.
270 to 380 nm for the Ge layer, 710 to 820 nm for the ZnS layer, and 6 for the metal fluoride layer.
When the antireflection film is provided on both surfaces of the substrate in the case of 30 to 800 nm, the substrate has an average transmittance of 93% or more in the infrared region of 2 to 5 μm.

The substrate is made of Si, and the optical thickness range of each layer is 55 to 220 nm for the Al ₂ O ₃ layer.
When the Ge layer has a thickness of 100 to 470 nm, the ZnS layer has a thickness of 380 to 1380 nm, and the metal fluoride layer has a thickness of 615 to 1170 nm, when the antireflection film is arranged on both surfaces of the substrate, the substrate has an infrared region of 3 nm or less. It has an average transmittance of 95% or more in the range of ˜5 μm.

The substrate is made of Si and the optical film thickness of each layer is 40 to 130 nm for the Al ₂ O ₃ layer.
90 to 230 nm for the Ge layer, 200 to 870 nm for the ZnS layer, 39 for the metal fluoride layer.
When the antireflection film is arranged on both sides of the substrate in the case of 0 to 680 nm, the substrate has an average transmittance of 95% or more in the infrared region of 2 to 2.5 μm.

The substrate is made of Si and the optical film thickness of each layer is 80 to 120 nm for the Al ₂ O ₃ layer.
220 to 280 nm for Ge layer, 760 to 870 nm for ZnS layer, 7 for metal fluoride layer.
When the antireflection film is provided on both surfaces of the substrate in the case of 20 to 790 nm, the substrate has an average transmittance of 93% or more in the infrared region of 2 to 5 μm.

Further, the substrate is GaAs, and the range of the optical film thickness of each layer is 65 to 210 n for the Al ₂ O ₃ layer.
m and Ge layers are 110 to 440 nm, ZnS layers are 480 to 1300 nm, and metal fluoride layers are 810 to 1130 nm. When the antireflection film is placed on both sides of the substrate, the substrate is in the infrared region. 3-5μ
It has an average transmittance of 95% or more in the range of m.

Further, the substrate is GaAs, and the optical thickness range of each layer is 40 to 140 n for the Al ₂ O ₃ layer.
m and Ge layers are 80 to 230 nm, ZnS layers are 180 to 840 nm, and metal fluoride layers are 400 to 675 nm. When the antireflection film is arranged on both sides of the substrate, the substrate is in the infrared region. 2 to 2.5 μm
Has an average transmittance of 97% or more.

Also, the substrate is GaAs, and the range of the optical film thickness of each layer is 85 to 125 n for the Al ₂ O ₃ layer.
m and Ge layers are 210 to 270 nm, ZnS layers are 770 to 875 nm, and metal fluoride layers are 710 to 785 nm. When the antireflection film is placed on both sides of the substrate, the substrate is in the infrared region. The average transmittance is 93% or more in the range of 2 to 5 μm.

The substrate is Te, and the optical film thickness range of each layer is 25 to 140 nm for the Al ₂ O ₃ layer.
When the Ge layer has a thickness of 300 to 950 nm, the ZnS layer has a thickness of 470 to 1200 nm, and the metal fluoride layer has a thickness of 750 to 1200 nm. It has an average transmittance of 95% or more in the range of ˜5 μm.

[Brief description of drawings]

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

FIG. 2 is a cross-sectional explanatory view of an example of a vapor deposition apparatus used for manufacturing an infrared antireflection film of the present invention.

FIG. 3 is a diagram showing an infrared spectral transmittance of a substrate having an antireflection film for infrared region obtained in Examples 1 and 2 of the present invention.

FIG. 4 is a diagram showing an infrared spectral transmittance of a substrate having an antireflection film for infrared region obtained in Example 3 of the present invention.

FIG. 5 is a diagram showing an infrared spectral transmittance of a substrate having an infrared antireflection film obtained in Example 4 of the present invention.

FIG. 6 is a graph showing infrared spectral transmittance of a substrate having an infrared antireflection film obtained in Examples 5 and 6 of the present invention.

FIG. 7 is a diagram showing the infrared spectral transmittance of a substrate having an infrared antireflection film obtained in Examples 7 and 8 of the present invention.

FIG. 8 is a diagram showing infrared spectral transmittance of a substrate having an antireflection film for infrared region obtained in Example 9 of the present invention.

FIG. 9 is a diagram showing the infrared spectral transmittance of the substrate having the antireflection film for infrared region obtained in Examples 10 to 12 of the present invention.

FIG. 10 is a diagram showing the infrared spectral transmittance of the substrate having the infrared reflection preventing film obtained in Examples 13 and 14 of the present invention.

FIG. 11 is a diagram showing the infrared spectral transmittance of the substrate having the infrared antireflection film obtained in Examples 15 and 16 of the present invention.

FIG. 12 is a diagram showing the infrared spectral transmittance of the substrate having the infrared reflection preventing film obtained in Examples 17 to 19 of the present invention.

FIG. 13 is a diagram showing the infrared spectral transmittance of the substrate having the infrared antireflection film obtained in Examples 20 and 21 of the present invention.

FIG. 14 is a diagram showing the infrared spectral transmittance of the substrate having the antireflection film for infrared region obtained in Examples 22 and 23 of the present invention.

FIG. 15 is a diagram showing the infrared spectral transmittance of the substrates having the infrared antireflection film obtained in Comparative Examples 1 and 2 of the present invention.

[Explanation of symbols]

1 substrate (lens or window), 2 Al ₂ O
₃ layers, 3 Ge layer, 4 ZnS layer, 5 metal fluoride layer.

─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-4-221901 (JP, A) JP-A-6-313802 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) G02B 1/10-1/12

Claims (11)

(57) [Claims] 1. The substrate is Ge, Si, GaAs and Te.
A chalcogenide with a refractive index of 3 or more
It is glass and is provided on the substrate. In order from the substrate side, A
l ₂ O ₃ layer, Ge layer, ZnS layer, or four layers of metal fluoride layer
An infrared antireflection film comprising the metal fluoride
Is MgF ₂ , CeF ₃ , YF ₃ , ThF ₄ , CaF ₂ and
An antireflection film for infrared region, which is one kind selected from cryolite (Na ₃ AlF ₆ ) . 2. The substrate is Ge, and the range of the optical film thickness of each layer is 45 to 180 nm for the Al ₂ O ₃ layer, 180 to 570 nm for the Ge layer, and 4 for the ZnS layer.
00 to 1300 nm, 640 for metal fluoride layer
The infrared antireflection film according to claim 1, which has a thickness of ˜1160 nm. 3. The substrate is Ge, and the range of the optical film thickness of each layer is 35 to 90 nm for the Al ₂ O ₃ layer, 135 to 300 nm for the Ge layer, and 30 for the ZnS layer.
0 to 800 nm, 350 to 7 for metal fluoride layer
The antireflection film for infrared region according to claim 1, having a thickness of 00 nm. 4. The substrate is Ge, and the range of the optical film thickness of each layer is 60 to 105 nm for the Al ₂ O ₃ layer, 270 to 380 nm for the Ge layer, and 7 for the ZnS layer.
10 to 820 nm, 630 for the metal fluoride layer
The infrared antireflection film according to claim 1, which has a thickness of 800 nm. 5. The substrate is Si, and the range of the optical film thickness of each layer is 55 to 220 nm for the Al ₂ O ₃ layer, 100 to 470 nm for the Ge layer, and 3 for the ZnS layer.
80-1380 nm, 615 for metal fluoride layer
The infrared antireflection film according to claim 1, which has a thickness of ˜1170 nm. 6. The substrate is Si, and the range of the optical film thickness of each layer is 40 to 130 nm for the Al ₂ O ₃ layer, 90 to 230 nm for the Ge layer, and 20 for the ZnS layer.
0-870 nm, 390-6 for metal fluoride layers
The antireflection film for infrared region according to claim 1, having a thickness of 80 nm. 7. The substrate is Si, and the range of the optical film thickness of each layer is 80 to 120 nm for the Al ₂ O ₃ layer, 220 to 280 nm for the Ge layer, and 7 for the ZnS layer.
60 to 870 nm, 720 for the metal fluoride layer
The antireflection film for infrared region according to claim 1, which has a thickness of 790 nm. 8. The substrate is GaAs, and the range of the optical film thickness of each layer is 65 to 210 nm for the Al ₂ O ₃ layer and G
The e layer is 110 to 440 nm, the ZnS layer is 480 to 1300 nm, and the metal fluoride layer is 8 nm.
The infrared antireflection film according to claim 1, having a thickness of 10 to 1130 nm. 9. The substrate is GaAs, and the optical thickness range of each layer is 40 to 140 nm for the Al ₂ O ₃ layer and G
The e layer is 80 to 230 nm, the ZnS layer is 180 to 840 nm, and the metal fluoride layer is 400 nm.
The antireflection film for infrared region according to claim 1, having a thickness of ˜675 nm. 10. The substrate is GaAs, and the range of the optical film thickness of each layer is 85 to 125 nm for the Al ₂ O ₃ layer,
210 to 270 nm for the Ge layer, 770 to 875 nm for the ZnS layer, 7 for the metal fluoride layer.
The infrared antireflection film according to claim 1, which has a thickness of 10 to 785 nm. 11. The substrate is Te, the optical thickness range of each layer is 25 to 140 nm for the Al ₂ O ₃ layer, and Ge
300-950 nm for layers, 470-1200 nm for ZnS layers, 75 for metal fluoride layers.
The infrared antireflection film according to claim 1, which has a thickness of 0 to 1200 nm.