JP2006072031A - Antireflection film for infrared region, and infrared lens using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain an antireflection film for an IR region which is excellent in environmental resistance, particularly in water resistance. <P>SOLUTION: The antireflection film for the IR region is provided on an IR optical substrate transmitting IR rays of 8 to 12 μm bands and is obtained by forming a ZnS layer 2, a Ge layer 3, a CeF<SB>3</SB>layer 4, and a CeO<SB>2</SB>layer 5 in this order on a substrate 1. Ge, ZnSe or chalcogenide glass having a refractive index of 2.4 to 4 in the IR region of 8 to 12 μm bands is used for the substrate. The CeF<SB>3</SB>is a low refractive index material having relatively high durability, and further, the CeO<SB>2</SB>having high adhesion to the CeF<SB>3</SB>and the extremely high durability is arranged as a protective layer on the CeF<SB>3</SB>layer, and therefore, antireflection film for the IR region having the excellent environment resistance, particularly water resistance as a whole is obtained. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an antireflection film for infrared region used for an optical member in an infrared region of 8 to 12 μm band, and an infrared lens provided with the same.

In order to obtain excellent antireflection characteristics, an antireflection film used for lenses and windows needs to be provided with a low refractive index material in the outermost layer. In the infrared region of 8 to 12 μm used in an infrared camera, the above-mentioned low A metal fluoride such as CaF ₂ , BaF ₂ , PbF _2, or LaF ₃ is used as the refractive index material, but water resistance, wear resistance, solvent resistance, and the like are not sufficient.
For this reason, there is one that imparts high durability by disposing a ZnS layer above the metal fluoride (see, for example, Patent Document 1).
In addition, YF ₃ excellent in environmental resistance such as water resistance and moisture resistance is used as the low refractive index layer, or Y ₂ O ₃ is disposed as a wear-resistant reinforcing layer on the YF ₃ layer. Some films are provided with high-performance films (for example, see Patent Document 2).

JP 59-17502 A (first page) JP-A-6-313802 (first page)

However, in the infrared antireflection film shown in Patent Document 1, the fluoride layer and the ZnS layer disposed as the outermost layer as the protective film do not always have high adhesion, and sufficient durability is obtained. Is not limited.
YF ₃ is certainly superior in water resistance and moisture resistance compared to BaF ₂ and LaF ₃ , but it is not sufficient. In particular, the adhesion with Ge is not so strong, and when Ge is disposed in the underlayer of YF ₃ , peeling occurs in a relatively short water resistance test or moisture resistance test.
Further, as shown in Patent Document 2, Y ₂ O ₃ as a protective layer, high wear resistance showed excellent adhesion in combination with YF ₃ is obtained. However, the effect of improving water resistance is small, and YF ₃ and other fluoride layers do not have sufficient water resistance and moisture resistance. Therefore, even if Y ₂ O ₃ layer and fluoride layer are combined, sufficient water resistance or There is a problem that moisture resistance cannot be obtained.

  The present invention has been made to solve such problems, and an object of the present invention is to obtain an antireflection film for infrared region excellent in environmental resistance, particularly water resistance, and an infrared lens using the same. .

The first antireflection film for infrared region according to the present invention is an antireflection film for infrared region formed on an infrared optical substrate that transmits infrared of 8 to 12 μm band, and ZnS provided on the substrate. A layer, or an alternating layer of ZnS and Ge, a CeF ₃ layer provided on the ZnS layer or an alternating layer of ZnS and Ge, and a CeO ₂ layer provided on the CeF ₃ layer It is characterized by.

The first antireflection film for infrared region of the present invention is an infrared region antireflection film formed on an infrared optical substrate that transmits infrared rays of 8 to 12 μm band, and is a ZnS layer provided on the substrate. Or an alternating layer of ZnS and Ge, a CeF ₃ layer provided on the ZnS layer or an alternating layer of ZnS and Ge, and a CeO ₂ layer provided on the CeF ₃ layer. It has the effect of obtaining an antireflection film for infrared region that is excellent in environmental resistance, particularly water resistance.

Embodiment 1 FIG.
In the antireflection film for infrared region according to the first embodiment of the present invention, a ZnS layer or an alternating layer of a ZnS layer and a Ge layer is disposed on a substrate to be a lens or a window, and further on the ZnS layer or the ZnS layer. A CeF ₃ layer is provided on alternating layers of Ge and Ge, and a CeO ₂ layer is provided on the CeF ₃ layer. Specific examples are shown in the following examples.
In the antireflection film for infrared region according to the present embodiment, CeF ₃ is a low refractive index material with relatively high durability, and CeO ₂ having high adhesion with CeF ₃ and extremely high durability is further formed thereon. Since the protective layer is disposed, an antireflection film for infrared region excellent in environmental resistance, in particular, water resistance as a whole can be obtained.
In the above-described antireflection film for infrared region, the thickness (physical film thickness) of CeO ₂ is preferably more than 50 nm and less than 500 nm. If it is 500 nm or more, the internal tensile stress of CeO ₂ becomes high and the risk of cracking in the film increases, and if it is 50 nm or less, it is difficult to obtain a sufficient effect as a protective layer of CeO ₂ .

  In addition, in the antireflection film for infrared region of the present embodiment, as a substrate material for a lens or a window, there is no absorption in the infrared region of 8 to 12 μm, the refractive index is 4, and the refractive index is 2.4. When using certain ZnSe or chalcogenide glass having a refractive index of 2.4 to 4 {product name: GASIR1, manufactured by UMICORE Co., Ltd.}, {product name: GASIR2, manufactured by UMICORE Co., Ltd.} In addition, a window or a lens excellent in environmental resistance can be obtained.

In the manufacturing method of the antireflection film for infrared region of the present embodiment, ZnS or ZnS and Ge are alternately deposited on a substrate to be a lens or a window, CeF ₃ is deposited thereon, and CeF _{3 is} further deposited. In the method of depositing CeO ₂ on the substrate, the substrate temperature is set to 150 ° C. or lower when depositing the ZnS, and the substrate temperature is set to 250 ° C. to 400 ° C. when depositing CeF ₃ and CeO _2. preferable.
By making the substrate temperature 150 ° C. or lower when depositing ZnS, it becomes a good film without white turbidity, and when depositing CeF ₃ and CeO ₂ , the substrate temperature is 250 ° C. to 400 ° C. A film is obtained and becomes a highly durable antireflection film.
In addition, in the antireflection film for infrared region of the present embodiment, an optically unrelated thin layer may be provided between the optical thin film and the substrate or between the layers, for example, for the purpose of improving adhesion. .

Embodiment 2. FIG.
The infrared lens according to the second embodiment of the present invention can be obtained by providing the infrared ray antireflection film according to the first embodiment on a lens that transmits infrared rays in the 8 to 12 μm band. A combined lens for infrared optics is manufactured by combining them. The single lens or group lens for the infrared region obtained as described above has the antireflection film of the first embodiment, so that it is excellent in environmental resistance and has excellent transmittance. It becomes a group lens.

Examples 1-3.
FIG. 1 is a configuration diagram of an antireflection film for infrared region according to Examples 1 to 3 of the present invention, which is a substrate for infrared optics that transmits infrared light in the 8 to 12 μm band, and is a Ge and chalcogenide glass whose both surfaces are polished. {Product name: GASIR2, manufactured by UMICORE Co., Ltd.} or ZnSe substrate 1 by optical deposition (= refractive index × physical film thickness) with ZnS layer 2 and Ge layer 3 according to the vacuum deposition method. The CeF ₃ layer 4 and the CeO ₂ layer 5 can be manufactured in this order as shown in FIG.

Here, the optical film thickness shown in Table 1 is the center wavelength (10 μm) of incident light from the substrate 1 by the ZnS2 of the first layer and the Ge3 of the second layer from the substrate 1 when the refractive index of the substrate is 2.4-4. ), A two-layer equivalent film equivalent to a quarter-wave film is formed, and a CeF ₃ 4 quarter-wave film is formed on the third layer thereabove to form a good antireflection film. Therefore, the multilayer film configured based on the multilayer film is finally determined by performing the film thickness optimization by the computer.
CeO ₂ has been calculated in advance as a protective layer so that a physical film thickness of 100 nm is arranged in the outermost layer in advance, but a thickness of 100 nm is expected to have a sufficient effect from the viewpoint of environmental resistance. And is sufficiently thin optically and has almost no influence on the antireflection effect.
FIG. 2 is a diagram of the spectral reflectance curve of the antireflection film for infrared region of the present example, and lines a1 to a3 are spectral reflectance curves of Example 1 to Example 3, respectively, and a predetermined wavelength region in the infrared region. It can be seen that the reflectance is sufficiently low in practical use.
Further, the Ge substrate on which the antireflection film of Examples 1 to 3 was formed was left in pure water at a water temperature of 23 ° C., and Table 2 shows the number of days until peeling.

FIG. 3 is a configuration diagram of a vacuum vapor deposition apparatus used for manufacturing the antireflection film for infrared region of this example.
That is, the substrate 6 for vapor deposition is attached to the substrate attachment dome 7 and rotated during vapor deposition to improve uniformity. A necessary amount of the vapor deposition material 8 is put in a crucible, placed on the rotary stage 9, and the vapor deposition material 8 is moved to a position where the electron beam strikes by rotating the rotary stage. When the vapor deposition material 8 in the crucible is heated by the electron beam emitted from the electron gun 10, the evaporated vapor deposition material is vapor deposited on the surfaces of the vapor deposition substrate 6 and the monitor substrate 11 to form a film. The thickness of the deposited film is monitored by the optical film thickness meter 13 mounted above the vacuum vessel 12 during the deposition, and the shutter 14 is closed when the desired thickness is reached. . In the same manner, the antireflection film for infrared region according to the embodiment of the present invention can be obtained by sequentially forming the deposited films of different layers by a predetermined thickness.
In the embodiment of the present invention, the optical thin film is formed by the electron beam vacuum vapor deposition method. However, not only the electron beam method is used for heating the vapor deposition material, but also a resistor that is heated by flowing a current through a metal crucible. A heating method can also be used. In addition, as a film thickness meter, not only an optical method for reading a change in reflected light and a change in transmitted light, but also a crystal vibration type film thickness meter may be used.
With the above apparatus, in this embodiment, an antireflection film is formed by setting the substrate temperature to 100 ° C. by the heater 15 when depositing the ZnS layer and setting the substrate temperature to 325 ° C. when depositing the Ge layer, CeF ₃ layer, and CeO ₂ layer. did.

Example 4,5.
FIG. 4 is a configuration diagram of an antireflection film for infrared region according to Examples 4 and 5 of the present invention, which is a substrate 1 whose both surfaces are polished, a chalcogenide glass {trade name: GASIR2, UMICORE Co., Ltd.} substrate or ZnSe. A ZnS layer 2, a CeF ₃ layer 4, and a CeO ₂ layer 5 are formed on the substrate in this order as shown in FIG. 4 by the same vacuum deposition method as in Example 1 with the optical film thicknesses shown in Table 3. Can be manufactured.

Here, when the refractive index of the substrate is 2.6 of chalcogenide glass and 2.4 of ZnSe, the optical film thickness shown in Table 3 is the central wavelength (10 μm) of incident light due to ZnS of the first layer from the substrate. A good anti-reflection film can be formed by forming a 1/4 wavelength film of CeF _{3 on} the second layer above it, so that a multilayer film formed based on that can be formed. The film thickness was optimized by a computer and finally decided.
As for CeO ₂ of the fifth layer, a physical film thickness of 100 nm was arranged in the outermost layer as in Examples 1-3.
FIG. 5 is a diagram of a spectral reflectance curve of the antireflection film for infrared region according to the present example. Lines a4 and a5 are spectral reflectance curves of Example 4 and Example 5, respectively, and a predetermined wavelength region in the infrared region. It can be seen that the reflectance is sufficiently low in practical use.
Further, the Ge substrate on which the antireflection films of Examples 4 and 5 were formed was left in pure water at a water temperature of 23 ° C., and the number of days until peeling is shown in Table 2.

Example 6,7.
FIG. 6 is a configuration diagram of an antireflection film for infrared region according to Examples 6 and 7 of the present invention, which is a substrate 1 whose both surfaces are polished, a chalcogenide glass {trade name: GASIR2, made by UMICORE Co., Ltd.} substrate or The Ge layer 3, the ZnS layer 2, the Ge layer 3, the CeF ₃ layer 4, and the CeO ₂ layer 5 are formed on the ZnSe substrate by the same vacuum deposition method as in Example 1 with the optical film thickness described in Table 4. As shown, it can be manufactured by forming in this order.

Here, when the refractive index of the substrate is 2.6 of the chalcogenide glass and 2.4 of ZnSe, the optical film thickness described in Table 4 is the first layer of Ge, the second layer of ZnS, A third-layer equivalent film equivalent to a quarter-wave film of the center wavelength (10 μm) of incident light is formed by the third-layer Ge, and a CeF ₃ quarter-wave film is formed on the fourth layer thereabove. Since a good antireflection film can be formed by forming the film, the multilayer film formed based on the film is finally determined by performing a film thickness optimization by a computer.
The fifth layer of CeO ₂ was arranged with a physical film thickness of 100 nm as the outermost layer as in Examples 1-3.
FIG. 7 is a diagram of a spectral reflectance curve of the antireflection film for infrared region according to the present example. Lines a6 and a7 are spectral reflectance curves of Example 6 and Example 7, respectively, and a predetermined wavelength region in the infrared region. It can be seen that the reflectance is sufficiently low in practical use.
Further, the Ge substrate on which the antireflection film according to Examples 6 and 7 is formed is left in pure water having a water temperature of 23 ° C., and the number of days until peeling is shown in Table 2.

Examples 8 and 9.
In Example 1, except that the outermost CeO ₂ layer was changed to a physical film thickness of 50 nm and 500 nm, an antireflection film for infrared region was formed in the same manner as in Example 1 for both the manufacturing method and the optical film thickness. did. Further, the Ge substrate on which these antireflection films are formed is left in pure water at a water temperature of 24 ° C., and the number of days until peeling is shown in Table 2.

Example 10
FIG. 8 is a configuration diagram of a combined lens using the infrared lens of Example 10 of the present invention. A lens made of Ge processed into a convex lens and a chalcogenide glass ({trade name: GASIR2, made by UMICORE Co., Ltd.} lens are prepared. In the same manner as in Example 1 for the Ge lens and in the same way as in Example 6 for the chalcogenide glass lens, each of the two infrared reflection films of this example was formed by forming an antireflection film for infrared region. Lenses 16 and 17 were obtained, and these two infrared lenses were combined using a lens barrel 18 to produce a two-lens set lens.
The assembled lens of this example was exposed to a relative humidity of 95% and a temperature of 40 ° C. for 10 days. However, the antireflection film was not peeled off or clouded, and the lens performance was not deteriorated.

Comparative Example 1
In Example 1, an antireflection film for infrared region was formed in the same manner as in Example 1 except that the outermost layer of CeO ₂ was omitted. Further, the Ge substrate on which this antireflection film is formed is left in pure water, and the number of days until peeling is shown in Table 2.

Comparative Example 2
In Example 1, the third layer from the substrate is YF ₃ , the fourth layer is Y ₂ O ₃ , and the optical film thickness is 2.291 μm and 0.16 μm, respectively. The antireflection film for infrared region is formed by the method, the Ge substrate on which this antireflection film is formed is left in pure water, and the number of days until peeling is shown in Table 2.

Comparative Example 3
Example 4 is the same as Example 4 except that the second layer from the substrate is YF ₃ , the third layer is Y ₂ O ₃ , and the optical film thicknesses are 2.058 μm and 0.16 μm, respectively. The antireflection film for infrared region was formed by the method. Further, the Ge substrate on which this antireflection film is formed is left in pure water, and the number of days until peeling is shown in Table 2.

As described above, since the antireflection film for infrared region according to the embodiment of the present invention has the CeF ₃ layer having a low refractive index disposed on the ZnS layer provided on the substrate or on the alternating layer of ZnS and Ge, It can be seen that the reflectance is sufficiently low in practical use in a predetermined wavelength region in the infrared region.
In addition, as shown in Table 2, the CeF ₃ layer has a high adhesion with ZnS and Ge and good moisture resistance, and a CeO ₂ layer having excellent environmental resistance is disposed in the outermost layer, and the CeO ₂ layer It can be seen that the film is particularly excellent in water resistance and other environmental resistance because of the high adhesion between the Al and CeF ₃ layers.

It is a block diagram of the antireflection film for infrared region of Examples 1-3 of the present invention. It is a figure of the spectral reflectance curve of the antireflection film for infrared region of Examples 1-3 of the present invention. It is a block diagram of the vacuum evaporation system used for manufacture of the antireflection film for infrared region of the Example of this invention. It is a block diagram of the antireflection film for infrared regions of Examples 4 and 5 of the present invention. It is a figure of the spectral reflectance curve of the antireflection film for infrared region of Examples 4 and 5 of the present invention. It is a block diagram of the antireflection film for infrared regions of Examples 6 and 7 of the present invention. It is a figure of the spectral reflectance curve of the antireflection film for infrared regions of Examples 6 and 7. It is a block diagram of the group lens using the infrared lens of the Example of this invention.

Explanation of symbols

1 substrate, 2 ZnS layer, 3 Ge layer, 4 CeF ₃ layer, 5 CeO ₂ layer, 16 infrared lens, 17 infrared lens.

Claims (3)

An antireflection film for infrared region formed on an infrared optical substrate that transmits infrared light of 8 to 12 μm band, the ZnS layer provided on the substrate, or alternating layers of ZnS and Ge, and the ZnS layer Or an antireflection film for infrared region, comprising: a CeF ₃ layer provided on alternating layers of ZnS and Ge; and a CeO ₂ layer provided on the CeF ₃ layer. 2. The antireflection film for infrared region according to claim 1, wherein the substrate is Ge, ZnSe, or chalcogenide glass having a refractive index of 2.4 to 4 in an infrared region of 8 to 12 μm. An infrared lens comprising a lens that transmits infrared rays in the 8 to 12 μm band, and the antireflection film for infrared region according to claim 1 or 2 formed on the lens.

Images