JP2003302520A - Reflection mirror for infrared laser and method for manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a reflection mirror for an IR laser having reflectivity exceeding 99.5%. <P>SOLUTION: A plurality of sets of alternate multilayered films combined with ZnSe or Zns as low-refractive index layers and Ge as high-refractive index layers on a silicon or oxygen-free silicon substrate are formed by ion assisted vapor deposition. At this time, the film thickness (f) of the low-refractive index layers is f=λcosecθ/4n<SB>1</SB>(λ is an IR wavelength, θ is the reflection angle in the layers and n<SB>1</SB>is a reflective index) and the film thickness (e) of the high- refractive index layers is e=λcosecϕ/4n<SB>h</SB>(λ is the IR wavelength, ϕ is the reflection angle in the layers and n<SB>h</SB>is the reflective index). The Ge on the surface is amorphous and hardly oxidized. The adhesion propery can be enhanced by incorporating HfO<SB>2</SB>(halfnium oxide) and Bi<SB>2</SB>O<SB>3</SB>(bismuth oxide) as binder layers into these layers. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a red mirror such as a bend mirror or a folding mirror inside a laser resonator used in a laser transmission optical system of an infrared laser processing system including a high-power carbon dioxide laser (CO ₂ ). It relates to an optical component for an outer laser. These reflective optical components for infrared lasers are required to have high reflectance and low absorptance. If the mirror absorbs, the laser power applied to the object to be processed becomes insufficient. Also, the mirror is overheated and deteriorates. Therefore, absorption should be as small as possible.

Here, the reflectance and the absorptance have a complementary relationship. It is difficult to measure reflectance directly. Therefore, absorption rate is often measured. Laser calorimetry
The metry method is a method of obtaining the absorption of laser power by measuring the temperature rise of the mirror. Since the value obtained by subtracting the absorptivity from 1 is the reflectance, the reflectance is calculated by absorption measurement.

A folding mirror is a mirror that forms a resonator. This is a 180 degree reflection and only two sheets are required. The bend mirror is a mirror for reflecting a laser beam repeatedly at a certain angle and irradiating an object through a desired path. Even if the reflectance of one mirror is close to 1, when the multiple mirrors are combined and multiple reflection is performed, the reflectance as a whole gradually decreases. If the reflectance of the jth mirror is R _j , then the overall reflectance is the product ΠR _j
Given by. Therefore, when the number of mirrors increases, the absorption increases, and the laser power applied to the object becomes insufficient.

[0004]

_2. Description of the Related Art In high-power carbon dioxide laser (CO ₂ : oscillation wavelength 10.6 μm) laser processing, an output mirror using ZnSe, a final stage mirror and a condenser lens are used for a laser oscillator system and a focusing system. To be This is because ZnSe is a material that is transparent to infrared light. That is, ZnSe itself is processed into a mirror, and ZnSe itself is processed into a lens.

Further, as the bend mirror of the transmission system, a mirror using Si (silicon) or Cu (oxygen-free copper) as a substrate material is used. These materials are selected because they are durable, have good thermal conductivity, and are easily attached to gold or silver. It is opaque to infrared. Si and Cu are 10.6 μm for carbon dioxide laser
Since the reflectance of light is not so good, gold or silver is deposited on the surface.

FIG. 1 shows a reflective mirror having a substrate coated with gold. FIG. 2 shows a reflective mirror with a silver coating on the substrate. Such a material has a reflectance of 99%. In practice, an intermediate layer is often inserted between the base material and gold or silver to obtain adhesion, but this is briefly shown here. This is expressed as gold / base material and silver / base material. Since it's similar, write only gold and base material, and let's say simply gold / base material.

The base material Si and oxygen-free copper (Cu) are cooled by cooling water to prevent deterioration due to laser beam heating. The reflectance becomes about 99% by vapor deposition of gold (Au) and silver (Ag). It seems that most of the layers have a high reflectance and a low absorptance (1%), but when a number of such mirrors of gold / base material are combined, absorption increases and the overall reflectance decreases. Then, the power of laser processing that hits the object is insufficient. I want to increase the reflectance at either 0.1% or 0.3%.

In particular, a plurality of transmission reflection mirror optical components (8 to 8) are provided up to the processing point from the laser oscillator to the condenser lens.
Arrange as many as 10 mirrors. Thereby, the optical path of the laser beam is changed to guide the beam to a predetermined position. Even if the reflectance of individual gold (silver) / base material mirrors is as high as 99.0% or more, when used as many (bend) mirrors in the transmission line, the laser light intensity is close to 10% due to multiple reflections. There is a significant loss due to reflection and absorption. Part of the laser light is absorbed by the mirror and becomes heat, which loses energy and substantially reduces the transmission efficiency. Therefore, each mirror is required to have extremely high reflectance and extremely low absorption. 99.0% for gold / substrate mirrors
Will not be exceeded.

Therefore, in order to increase the reflectance to 99.0% or more, the reflectance is enhanced (reflection enhancement).
It has been attempted.

[Conventional method: (ZnSe / ThF ₄ ) ^m / A
u / Substrate; FIGS. 3 and 4] As a conventional method for enhancing the reflectance, there is a method using a dielectric multilayer film. This is a method of forming an alternate laminated film composed of two kinds of film materials of low refractive index fluoride (ThF ₄ ) and high refractive index ZnSe (zinc selenide) on a substrate coated with gold or silver. It is well known that the reflectance is increased by alternately laminating a low refractive index dielectric film having a thickness of λ / 4 and a high refractive index dielectric film having a thickness of λ / 4 on a substrate.

From the base material side, a high refractive index material is exposed in the outermost layer such as a base material, a low refractive index, a high refractive index, a low refractive index and a high refractive index. The number m of alternating multilayer film pairs may be any number of 1 or more. When the number of alternating multilayer film pairs is m, it is simply expressed as (high refractive index material / low refractive index material) ^m . The number of sets is m
So the number of layers is 2m.

The phase of the reflection on the surface and the phase of the reflection on the boundary surface become the same, and the reflections strengthen each other, so that the reflectance increases. ZnSe / ThF ₄ alternating laminated film (m
≧ 2) It is said that the reflectance can be increased by 0.5% to 99.5% by adding. For example, such a proposal is made in the following document.

AM Ledger, "Inhomogeneous Interfa
ce Laser Mirror Coatings ", AppliedOptics, vol.18,
No. 17, p2979-2989, 1 September 1979

In this method, gold or silver is vapor-deposited on a molybdenum substrate, and (ZnSe / ThF ₄ ) or (ZnSe /
S / ThF ₄ ) alternating multilayer films are formed. 3 and 4
Shows the cross-sectional view when m = 2. ZnSe on the right of the figure
The refractive index for each layer is shown, such as refractive index 2.4, ZnS refractive index 2.2, ThF ₄ refractive index 1.4.

The reflectance is extremely high with a relatively simple film structure. With this (m ≧ 2), the reflectance can be increased to 99.5%. That is, the reflectance can be increased by 0.5% compared with the gold / base material. It is said that a CrO ₂ film having a thickness of 30 nm should be used as a binder layer on gold or silver in order to enhance the adhesion with molybdenum. Since the reflectance is 99.5%, even if 7 to 8 bend mirrors are used in the transmission system, the absorptance is about 4% and the overall reflectance is 96%.

However, the reflection mirror using the fluoride ThF ₄ still has drawbacks. T for 10.6 μm light
The refractive index of hF ₄ is 1.4. The thickness of the dielectric film forming the reflective film is λ cosec θ / 4n (λ is the infrared wavelength, n is the refractive index, θ is the reflection angle; this formula will be described later).
Must be.

Therefore, the film thickness of ThF ₄ having a low refractive index becomes 1.9 μm even when θ is 90 degrees (minimum).
It is a fairly thick film. Moreover, it is not one pair but at least 2
It is necessary to pair (m ≧ 2). In that case, it is necessary to form two or more layers of ThF ₄ film as thick as 2 μm. It takes time to form a film. Since it takes time, there is a drawback that the film forming conditions are easily changed and it is difficult to form a film having uniform film quality. Further, fluoride has a problem that it absorbs water and its film quality deteriorates with age.

[0018]

Two types of conventional techniques have been described. 1. The gold / base material has a reflectance of about 99%. It can be as high as 99.3%. 2. The reflectance of (ZnSe / ThF ₄ ) ^m / gold / molybdenum is 99.5%. With the progress of laser processing technology, the laser power is increasing and the objects to be processed are expanding. The transmission system also tends to be complicated. The required laser power is also increasing.

In laser processing, it is necessary to use a plurality of (8 to 10) reflecting mirrors used in the transmission system. Therefore, the transmission efficiency of the laser energy as a whole is low. ZnSe / T with a reflectivity of 99.5%
Even if a mirror provided with a coating composed of an alternating multi-layered film of hF ₄ is used, it is sometimes impossible to obtain a sufficient power required for laser processing. Such lack of power has become a new issue.

Fluorescent ThF ₄ is used as the low refractive index film material in the mirrors that have been subjected to the reflection enhancing coating. Therefore, it has a difficulty in moisture resistance to moisture. There is a problem that the fluoride absorbs water and the light absorption rate as a mirror increases and the reflectance decreases due to long-term use.

Fluoride ThF_Four(N = 1.4)
When used as a film-forming material, the optical thickness is λ cosec θ
Infrared laser wavelength, for example,
CO _TwoAbout 2μ for laser wavelength (10.6μm)
An extremely thick film of m is required. Thick film as mentioned above
It takes time to form a film, and the quality varies.
There is a point.

If the constituent layers must be two or more layers (m ≧ 2), the number m of layers increases and the occurrence of surface scattering and the inclusion of impurities, film defects and the like increase. Therefore, there is also a problem that the film quality is deteriorated.

Also, the membrane material used (ThF ₄ ) is not robust. There were also problems with mechanical durability and film peeling during long-term use. As described above, the reflection enhancing film using fluoride as a low refractive index has drawbacks such as lack of reflectance, difficulty in film formation, quality variation, water resistance, and film peeling.

There has been a strong demand from users for a reflecting mirror which has a high reflectance and a very low absorptivity, has a high durability of the mirror surface in terms of handling, and does not change with time.

The present invention has a high reflectance (absorption rate of 0.2%) of more than 99.5%, preferably 99.8% or more.
The first object is to provide an infrared reflecting mirror that can obtain the following.

A second object of the present invention is to provide an infrared reflecting mirror in which the adhesion between the coating layer and the base is enhanced so that film peeling does not occur.

A third object of the present invention is to provide an infrared reflection mirror in which the film thickness of the dielectric film is reduced and the film formation time can be shortened.

A fourth object of the present invention is to provide an infrared reflecting mirror having excellent water resistance and durability.

[0029]

The reflector of the present invention comprises a silicon or oxygen-free copper substrate coated with gold or silver, and with a thickness corresponding to a quarter wavelength with or without a binder layer. (Λ cosec θ / 4n _l ) ZnSe layer or ZnS layer and thickness (λ cos
Two or more sets (m ≧ 2) of alternating multilayer films composed of Ge layers of ecφ / 4n _h ) are formed by the ion assisted vapor deposition method. The thickness corresponding to a quarter wavelength is λ cosec θ / 4n, where θ is the inclination angle. It will be described later.

The ion assist method is a method of vacuum vapor deposition while applying an ion beam to a sample. It is performed by an ion assist device provided with an ion source and a vapor deposition source in the same vacuum chamber. Ions are argon (Ar) and xenon (Xe). The acceleration energy of the ion beam and the beam current are parameters.

In the case of vapor deposition of ZnSe and ZnS (low refractive index film), the acceleration energy is 150 eV to 250 eV and the ion beam current density is 10 to 30 μA / cm ² . The device used by the inventor has an ion beam current of 20
It was ~ 50 mA. In the case of Ge vapor deposition (high refractive index film),
The acceleration energy is 150 eV to 250 eV, and the ion beam current density is 20 to 40 μA / cm ² . The apparatus used by the present inventor has an ion beam current of 30-60.
It was mA.

The film forming temperature at the time of forming the ZnSe film, the ZnS film and the Ge film is 200 ° C. to 270 ° C.

The binder layer described above may be omitted, and the ZnSe layer may be directly vapor-deposited on the gold (silver) layer. However, if the binder layer is sandwiched between them, the adhesion is enhanced.

When the binder layer is provided, hafnium oxide (HfO ₂ ) or bismuth oxide (Bi ₂ ) is formed on the gold-coated surface of the base material (Si, Cu) coated with gold (silver).
O ₃ ) is coated as a binder layer. The preferable thickness of the binder layer is 0.05 μm to 0.15 μm. Hf
O ₂ and Bi ₂ O ₃ are materials that have little absorption in the infrared region and can enhance adhesion. In the above-mentioned conventional example, chromium oxide (CrO ₂ ) is used as the binder layer.
This is because the substrate is molybdenum (Mo) and the ThF ₄ thin film is attached. In the case of the present invention, the base material is Si, Cu, Z
Attach an nSe (ZnS) thin film. In that case, HfO ₂ ,
The present inventors have for the first time found that Bi ₂ O ₃ is suitable. Such a thing was discovered only after repeated experiments.

For the low refractive index film material L, ZnSe or ZnS having no hygroscopic property is selected. In the above, these were used as high refractive index films, but in the present invention they are used as low refractive index films. ZnSe for 10.6 μm light of carbon dioxide laser
Has a refractive index of n _l = 2.4, and ZnS has a refractive index of n _l = 2.
It is 2. Since it is a dielectric multilayer film for reflection, the refractive index × film thickness must be equal to wavelength / 4. The film thickness f is f = λ cosec θ / 4n _l .
θ is the tilt angle. In the case of a bend mirror, θ is often not 90 degrees, but if angle is taken into consideration, the story becomes complicated, so θ
Will be compared at 90 degrees. When it is 90 degrees, it is the thinnest, so it becomes larger when tilted. General angles will be described later.

When θ = 90 degrees, the ZnSe film thickness is 1.1.
μm, and the ZnS film thickness is 1.2 μm. Both are almost 1
A thin one with μm is good. Since ThF ₄ used as a low refractive index film in the conventional example is n = 1.4, θ =
In the case of 90 degrees, a film thickness of about 2 μm is required. It took a long time to form a film, which was a factor of reducing reliability. The present invention can reduce the film thickness of the low refractive index film to 1 μm by adopting ZnSe and ZnS. The film formation time is halved and the process reliability is improved. ThF ₄ was hygroscopic, but ZnSe, Z
nS has no hygroscopicity and is stable.

Germanium (Ge) is used for the high refractive index film material. This means that for light having a refractive index of 10.6 μm, n _h = 4
Extremely high at. High refractive index is a very useful property. Not only that, it has no hygroscopicity and high mechanical strength. Moreover, there is an advantage that the film durability is high. The film thickness e of germanium (Ge) corresponding to a quarter wavelength is e = λ cos
ecφ / 4n _h (φ is an inclination angle), and is 0.66 μm when the carbon dioxide laser wavelength is 10.6 μm and φ = 90 degrees. It means that a thin film is enough.

In the present invention, ZnSe or ZnS (low refractive index film) having a thickness corresponding to λ cosec θ / 4n _l and λ co
Ge (high refractive index film) with a thickness corresponding to secφ / 4n _h
Are alternately laminated on the binder layer (or the gold layer) in units of an even number of 4 or more (m is 2 or more). Thereby, a high reflectance (low absorptance) is realized.

Ion-assisted vapor deposition, which performs vapor deposition while irradiating an ion energy beam of relatively low ions, is applied to the formation of the low-refractive index film and the high-refractive index film which will be the reflection enhancing layer.
Ion-assisted vapor deposition is normal vapor deposition with ion beam irradiation added. A low-energy rare gas ion beam of about several hundred eV is applied to the sample surface to strengthen the deposited film.
The low energy is for suppressing changes in chemical composition, such as decomposition of constituent molecules.

As a result, the Ge layer of the high refractive index film has an amorphous film structure in whole or in part, and the film quality with extremely high density is improved. Further, the progress of oxidation of the Ge film, which is seen in vacuum vapor deposition by a usual electron beam, is suppressed, and a highly reflective mirror with high durability can be realized.

[0041]

DETAILED DESCRIPTION OF THE INVENTION The present invention is directed to HfO ₂ , Bi ₂ O on gold or silver coated silicon or oxygen free copper substrates.
ZnSe or ZnS (low-refractive index film) by ion-assisted deposition and Ge (high-refractive index film) by ion-assisted deposition with or without intervening binder layer ₃
Provided is a reflection mirror for infrared light, which is formed by alternately forming and.

The substrate is silicon or oxygen free copper.
The binder layer is HfO ₂ or Bi ₂ O ₃ . This improves the adhesion between the alternate multilayer film and the substrate. The thickness of the binder layer is preferably 0.05 μm to 0.15 μm.

When forming the binder layer, 300 eV
The surface is cleaned by applying an ion beam of ˜600 eV for 5 to 10 minutes.

The low-refractive index film and the high-refractive index film are subjected to ion-assisted vapor deposition. Ion-assisted vapor deposition is to apply a low-energy rare gas ion beam simultaneously with vapor deposition. The collision of the ion beam activates the surface state to form a dense film. The energy of the ion beam is 150 eV to 250 eV. Film formation temperature is 200 ℃
˜270 ° C.

Vacuum evaporation is a technique in which a material placed in a crucible in a vacuum chamber is heated and evaporated to be deposited on a substrate. The heater itself may be resistance-heated as a boat-shaped crucible. If the melting point of the material is high, resistance heating cannot be performed, so the material is put in a crucible and heated by applying an electron beam. In the case of ZnSe, ZnS, and Ge, although resistance heating can be performed, electron beam heating can also be used for evaporation. Therefore, the vacuum chamber is provided with both an ion source that generates an ion beam and a vapor deposition source.

When vapor deposition is performed while activating the surface with an ion beam, a denser and more robust film can be formed than ordinary vapor deposition. This is the reason why the ion assisted vapor deposition is adopted in the present invention. Although the film quality of ZnSe and ZnS is remarkably improved, the effect of ion-assisted deposition is rather Ge.
Remarkably appears on the membrane.

It was well known that Ge has a high refractive index of n = 4. However, a mirror having Ge as the uppermost layer has never been manufactured. There may be several reasons, but it seems that Ge is oxidized and deteriorated when it is used as the uppermost layer. Ge is originally a semiconductor that is easily oxidized. Ge left in the air is covered with a thin surface oxide film. If Ge is used for the uppermost layer of the reflection mirror, it is strongly heated in the air by the strong beam of the carbon dioxide laser, and the Ge surface is oxidized and becomes GeO ₂ and becomes cloudy in white. If this happens, the reflectance will decrease significantly and absorption will increase. It will absorb the heat of the carbon dioxide laser beam and break and burst in a short time.

For this reason, Ge was known to have a high refractive index, but it was not used for the uppermost layer of the reflection mirror. One reason is that ZnSe is used as the uppermost layer (high refractive index film) in the above-mentioned conventional example.

However, it was found that Ge of the present invention was in the uppermost layer and did not deteriorate even when heated in air by a strong carbon dioxide laser beam. That is, it does not oxidize when heated in air. Why does Ge layer of the present invention do not oxidatively deteriorate while Ge formed by normal vapor deposition oxidizes?

The present inventor examined the reason. X
A line diffraction analysis revealed that no peak appeared at the diffraction angle that should appear in the Ge crystal. Further, no peak of oxidized Ge (GeO ₂ ) appears. This means that the Ge-specific periodic crystal structure no longer exists. That is, the Ge layer of the reflection mirror of the present invention is not polycrystal but amorphous. Although it became amorphous and had no crystal structure, the refractive index was maintained at 4. It is presumed that the refractive index of Ge does not depend on the crystal structure but on the electronic structure in the atom.
The Ge layer may be wholly or partially amorphous and therefore will not be oxidized by heating with an intense laser beam in air.

Why does amorphous Ge not oxidize?
The reason for this is still unknown to the present inventor. The dangling bond may disappear due to becoming amorphous. The reason is not clear, but it doesn't oxidize anyway. Since Ge does not oxidize, a clear surface can be maintained forever. Therefore, it becomes a long-life reflective mirror. That may be the main reason for enabling the reflective mirror having Ge as the uppermost layer for the first time.

Since the reflection mirror of the present invention has high moisture resistance and mechanical durability and has an extremely high reflectance (extremely low absorptance), when used as a bend mirror of a laser transmission system, transmission loss of laser power is caused. Can be significantly reduced.

Further, since the laser absorption by the mirror is extremely small, the quality of the laser processing due to the mirror is not deteriorated and stable performance can be exhibited for a long period of time.

Further, even if the mirror surface is soiled, the film is a robust film, so even if a relatively strong regeneration treatment (wiping or washing treatment using a solvent etc.) is carried out, there is no deterioration due to surface damage and the initial stage is obtained. It has a long life because the performance can be maintained.

Here, the principle of causing reflection of the dielectric multilayer film will be described. As is well known, it will be clarified why the film thickness limitation such as λ cosec θ / 4n is imposed.

FIG. 5 shows a high refractive index layer of m = 3 /
The case where light incident at a right angle on a reflection mirror formed of a low refractive index layer is reflected is shown. A low refractive index layer L ₁ , a high refractive index layer H ₁ , a low refractive index layer L ₂ , a high refractive index layer H ₂ , a low refractive index layer L ₃ and a high refractive index layer H ₃ are laminated from the base material side. . The high-refractive index layers H _j (j = 1, 2, 3) have the same thickness, which is referred to as e. The low-refractive-index layers L _j also have the same thickness, which is referred to as f. The refractive index of the high refractive index layer H is n _h , and the refractive index of the low refractive index layer L is n _l .

"At a right angle" means that the reflection angle Θ is 90 degrees. When a light ray is incident on a surface, the angle with the normal is called the incident angle, and the angle with the surface is called the reflection angle. They are in a complementary relationship with each other. B ₁ is a base material S and a first low refractive index layer L
₁ means the beam reflected at the boundary. B ₂ is a beam reflected at the boundary between L ₁ and the first high refractive index layer H ₁ .
Similarly, the beam is defined up to B ₇ .

B ₁ is a base material whose phase advances by 180 degrees. The optical path length is 2n ₁ f longer than B ₂ . 2 is attached because it reciprocates. If the phases of B ₁ and B ₂ match, the reflected lights of B ₁ and B ₂ will strengthen each other. Since the phase difference may be 360 degrees, the optical path length difference may be a half wavelength (180 degrees). That is, if 2n _lf = λ / 2, the phases of the reflected lights of B ₁ and B ₂ match and strengthen each other. B ₃ is reflected at the boundary between the low refractive index layer L ₂ and the high refractive index layer H ₁ , and the phase thereof changes by 180 degrees. If 2n _lf = λ / 2 by the same thing, the reflected lights of B ₃ and B ₄ will strengthen each other. The relationship between B ₅ and B ₆ is the same.

B ₂ is reflected at the boundary between the high refractive index and the low refractive index, and the phase does not change. The phase of B ₃ changes by 180 degrees.
So if the optical path length difference _2n h e = _λ / 2 of the high refractive index layer, _{B 2} and _{B 3} are constructive. That is, the high refractive index layer thickness e,
The low refractive index layer thickness f is

F = λ / 4n _l (1) e = λ / 4n _h (2)

In this case, the phases of the reflected lights B _{1 to} B ₇ match and strengthen each other. This is a right-angled reflection, which is the case with resonator mirrors.

In the case of a bend mirror, the reflection angle is not 90 degrees. Most of them are around 45 degrees. FIG. 6 illustrates the reflection of a generally tilted beam C ₀ . The reflection angle is Θ
And The beam tilt angle in the low refractive index layer is θ, and the beam tilt angle in the high refractive index layer is φ. Meanwhile, from Snell's law,

N ₀ cos θ = n _l cos θ = n _h cosφ (3)

There is a relationship of n ₀ is the refractive index in the atmosphere and is 1
Is.

S and L₁C reflected at the boundary of₁,
L₁And H₁C reflected at the boundary of_TwoAnd so on
Define 7 beams. C₁And C_TwoConsidering the difference in optical path length
Get C₁Is L₁2n in_lExtra light of fcosec θ
Go through the road. C_TwoIs 2n outside ₀remainder of fcotθcosΘ
Through the optical path of minutes. C₁Is 180 degrees in phase due to reflection
Mu. Therefore, if the optical path difference δ is λ / 2, the phases match and C₁
And C_TwoWill strengthen each other.

Δ = 2n _l fcosec θ−2n ₀ fcot θcos Θ = 2n _l fsin θ = λ / 2 (4)

To satisfy that, the thickness f of the low refractive index layer is

F = λ / 4n _l sin θ (5)

It is sufficient if At the same time, C ₃ and C ₄ , and C ₅ and C ₆ strengthen each other. By the same consideration, the thickness e of the high refractive index layer
But

E = λ / 4n _h sin φ (6)

It becomes Or use cosec expression

F = λ cosec θ / 4n _l (7) e = λ cosec φ / 4n _h (8)

It can also be written as Or using the reflection angle Θ in the air,

F = λ / 4 (n _l ² −cos ² Θ) ^1/2 (9) e = λ / 4 (n _h ² −cos ² Θ) ^1/2 (10)

It can also be written as In this specification, since expressions are easy to write, expressions (7) and (8) are used.
Any of (10) is the same. In this specification, the thickness f of the low refractive index layer and the thickness e of the high refractive index layer all have such clear meanings and values. It is well known to those skilled in the art to combine high refractive index and low refractive index to enhance reflection.

[0076]

EXAMPLE [Reflecting Mirror Layer Structure] FIG. 7 shows an example of the present invention.
The structure of the infrared reflection mirror concerning is shown. 4 mm to 6 mm
The base material is a thick Si single crystal. On Si substrate
A Cr layer of 0.1 μm and a gold layer of 0.3 μm are formed.
The gold layer forms the underlying reflective surface. Cr is gold Si
Improves adhesion to. 0.1 μm thick H on the gold layer
fO_TwoOr Bi_TwoO _ThreeThe binder layer of is formed. Ba
1.17 μm thick ZnSe is formed on the inder layer
To be done. ZnS may be used, but in that case the thickness is slightly different
come. A 0.67 μm Ge layer was formed on ZnSe.
It 1.17 μm ZnSe is formed on Ge.
A 0.67 μm Ge layer is formed on ZnSe.

This is an embodiment in which m = 2. 1.17μ
By alternately depositing m ZnSe and 0.67 μm Ge, it is possible to manufacture any number m. The top layer is always Ge. Ge has become amorphous. That is important. Therefore, it does not oxidize when heated in air.

[Reflection Mirror Manufacturing Method] Infrared 10.6 μm
Φ1.5 inch (38.1 mm) -4 mmt and φ3.0 inch (76.
(3 mm) -6 mmt optically polished single crystal silicon substrate (Si) was prepared. First, a chromium layer (Cr) and a gold layer (Au) were coated on the silicon surface by a direct current or RF sputtering method. The chromium layer is for ensuring the adhesion of the gold coating film to the silicon substrate, and has a film thickness of about 0.1 μm. The gold layer is a film for reflecting laser light and has a film thickness of about 0.3 μm.

In order to secure sufficient adhesion between the gold layer and the reflection enhancing layer, a hafnium oxide (HfO ₂ ) binder layer was formed by EB (electron beam) vapor deposition at a substrate temperature of 220 ° C. The film thickness was about 0.1 μm. Binder layer is A
It increases the adhesion between u and ZnSe. However, the HfO ₂ binder layer can be omitted.

Next, the surface of the HfO ₂ film as the binder layer was subjected to a cleaning treatment by irradiation with Xe (xenon) ion beam. Ion irradiation conditions for the cleaning treatment are an ion beam energy of 500 eV and a beam current of 40 mA. The processing time is 5 minutes.

Subsequent to the vapor deposition of the binder layer and the cleaning treatment, ion-assisted vapor deposition (ion-assisted vapor deposition) of an alternating four-layer film of ZnSe layers and Ge layers was performed.

An ion source is provided below the center of the vacuum chamber.
Lower left and right crucibles for electron beam heating evaporation (for Ge, Z
(for nSe), and the sample is placed downward on the support device above the central part. Ion assisted vapor deposition is to ionize and accelerate a rare gas such as Ar or Xe to hit a sample to activate the surface and strengthen the deposited film. The energy of the ions is set to the same level as the kinetic energy of the vapor deposition material on the sample surface.

The ion assist conditions for the ZnSe film of the low refractive index layer were an ion beam energy of 200 eV and a beam current of 20 mA.

The ion assist conditions for the high refractive index Ge film were ion beam energy of 200 eV and beam current of 40 mA.

The degree of vacuum during vapor deposition is 1.1 sccm of rare gas.
It was 6 × 10 ⁻⁵ Torr under the introduction, and the base vacuum degree (before introducing the rare gas) was 3 × 10 ⁻⁶ Torr. The absorptance of the manufactured reflection mirror was measured by a laser calorimetry method. Absorption rate is 0.19%,
The reflectance was 99.8%. This is the purpose 99.
It exceeds 5%. Conventional (ZnSe / Th
The reflectance is 0.3% higher than 99.5% of F ₄ ) ^m / gold / base material, which is excellent.

In order to see the layer structure, the cross section of the alternate multilayer film portion was observed by a high resolution scanning electron microscope (SEM). FIG. 8 shows a SEM photograph. Ge / ZnS from top to bottom
e / Ge / ZnSe / HfO ₂ / Au / Cr / Si (base material). The lower white part is Au, and the extremely thin part above it is HfO ₂ . ZnSe is a bumpy and bumpy part on it. Ge is a clear and flat part that can be seen in the middle. The bumpy portion just above that is ZnSe. The part with the fewest bumps is G
It is e. ZnSe having a rough cross section is polycrystal, but refreshed Ge looks like amorphous. The fact that it is amorphous can be understood from the fact that no line peculiar to the Ge crystal structure appears in the above-mentioned X-ray diffraction. Also, in vapor deposition Ge, a line of GeO ₂ always appears, but it does not appear. That is, the surface oxide film is not formed.

In order to evaluate the moisture resistance performance of the reflecting mirror, a high temperature and high humidity test (setting conditions; atmosphere temperature 50 ° C., relative humidity 95%, test time 24 hours) was carried out using a commercially available device. No surface deterioration such as fogging or film peeling was observed.

The absorptance of the reflective mirror that underwent the humidity resistance test was measured again, but again no change was observed at 0.19%.

Further, in order to evaluate the oxidation resistance of the reflection mirror, an optically polished Ge single crystal substrate was used as a comparative sample and left in the atmosphere at a high temperature of 100 ° C. to 120 ° C. for about 2 hours to prevent surface deterioration. Existence was investigated.

On the optically polished Ge single crystal substrate, local turbidity was observed due to the progress of oxidation. The outermost surface Ge film of the reflecting mirror of the present invention had sufficient oxidation resistance without any change.

Further, when the mirror surface is contaminated, a relatively strong regeneration process (wiping or cleaning process using a solvent or the like) can be performed because it is a robust film. Even if the solvent is wiped off or washed, the initial performance can be maintained without deterioration due to surface damage. It can be repeatedly recycled and has a long life.

[0092]

According to the present invention, the reflectance is high and the absorption rate is high.
Low, high humidity resistance, high mechanical strength, durability
It is possible to provide a reflection mirror having (Ge / Z
nSe) or (Ge / ZnS) dielectric multilayer film is used
Therefore, the reflectance is high. ThF _FourMoisture resistance because it does not use
Is improved. With ZnSe layer by ion assisted deposition
Since the Ge layer is formed, it becomes a dense film. High mechanical strength
Yes. Ge exposed in the uppermost layer is amorphized
Since it is hard to change, it has high durability. Also, the reflectance deteriorates for a long time.
do not do. H as a binder layer between the gold layer and the ZnSe layer
fO_TwoOr Bi _TwoO_ThreeIf you insert the
Will be excellent.

The maximum value of the reflectance so far is 99.5.
A reflectance as high as 0.3% can be provided.
Since it has an excellent high reflectance, the laser energy loss can be kept extremely low even when it is used in a transmission system that requires a plurality of mirrors. For example, even if eight bend mirrors are used, the absorption is 1.6% or less. Up to 98.4% of the power during laser oscillation reaches the object. Therefore, laser processing with sufficient power can be realized.

Further, since the reflecting mirror is composed of a robust film produced by the ion assist method, the surface is not damaged even if the surface is regenerated. Stable initial performance (high reflectance, low absorptivity) can be maintained for a long time, and it has a long life. As a result, it is effective in reducing the running cost of laser processing.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view showing a structure of an infrared reflection mirror according to a conventional example in which a gold layer (Au) is formed on a base material having a reflectance of 99% with respect to a carbon dioxide laser beam.

FIG. 2 is a longitudinal sectional view showing the structure of an infrared reflection mirror according to a conventional example in which a silver layer (Ag) is formed on a base material having a reflectance of 99% with respect to a carbon dioxide laser beam.

[Figure 3] AM Ledger, "Inhomogeneous Interface L
aser Mirror Coatings ", Applied Optics, vol.18, No.
17, p2979-2989, 1 September 1979 shows the structure of an infrared reflection mirror according to a conventional example having a (ZnSe / ThF ₄ ) alternating multilayer film and having a reflectance of 99.5% for a carbon dioxide laser. Vertical sectional view.

[Figure 4] AM Ledger, "Inhomogeneous Interface L
aser Mirror Coatings ", Applied Optics, vol.18, No.
17, p2979-2989, 1 September 1979 shows the structure of an infrared reflection mirror according to a conventional example having a (ZnS / ThF ₄ ) alternating multilayer film and having a reflectance of 99.5% for a carbon dioxide laser. Vertical sectional view.

FIG. 5: Dielectric multilayer film in which low refractive index films L _j and high refractive index films H _j are alternately laminated from the base material side is reflected by a 90 ° incident beam (normal incidence; reflection angle Θ = 90 °). Explanatory drawing explaining having the effect which raises a rate.

FIG. 6 shows a dielectric multilayer film in which low-refractive index films L _j and high-refractive index films H _j are alternately laminated from the base material side with respect to obliquely incident beams (oblique incidence; reflection angle Θ = 0 ° to 90 °). Explanatory drawing explaining that there is an effect of raising the reflectance.

FIG. 7 shows a chrome layer, gold or gold on a Si or oxygen free copper substrate.
Or silver layer, HfO_TwoOr Bi _TwoO_ThreeBinder layer, Z
nSe or ZnS low refractive index layer, Ge high refractive index layer, Zn
A low refractive index layer of Se or ZnS and a high refractive index layer of Ge are laminated.
A longitudinal section showing the structure of a reflection mirror for infrared laser of the present invention
Fig.

FIG. 8 Ge / ZnSe / Ge according to an embodiment of the present invention
High resolution scanning electron micrograph of a reflection mirror made of / ZnSe / HfO ₂ / Au / Cr / Si.

[Description of Reference Signs] H _{1 to} H ₃ high refractive index layer L _{1 to} L ₃ low refractive index layer n _h high refractive index layer refractive index n ₁ low refractive index layer refractive index e high refractive index layer thickness f Thickness of low-refractive index layer Θ Reflection angle in air θ Reflection angle in low-refractive index layer φ Reflection angle in high-refractive index layer m Number of alternate laminated film pairs

   ─────────────────────────────────────────────────── ─── Continued front page    F-term (reference) 2H042 DA04 DA05 DA08 DA12                 2H048 FA05 FA07 FA09 FA12 FA24                       GA04 GA07 GA09 GA19 GA33                       GA60 GA62                 4K029 AA02 AA06 BA05 BA07 BA41                       BA43 CA05 CA09 DC35 FA04

Claims (6)

[Claims] 1. A silicon or oxygen-free copper substrate, a gold layer or a silver layer coated thereon, and a HfO ₂ (oxidation of 0.05 μm to 0.15 μm) layer formed on the gold or silver layer. Hafnium) or Bi ₂ O ₃ (bismuth oxide) and a film thickness f formed by ion-assisted deposition is f = λ cosec θ / 4n ₁ (λ is an infrared wavelength, θ is a reflection angle in the layer, n _l is the refractive index) Zn
A low refractive index layer of Se (zinc selenide) or ZnS (zinc sulfide) and a film thickness e formed by ion assisted vapor deposition are e = λ cosec φ / 4n _h (λ is an infrared wavelength, φ is reflection in the layer). The corners, n _h is the refractive index) are composed of m high-refractive-index layers made of Ge (m ≧ 2), and are alternately laminated films provided on the binder layer.
A reflection mirror for an infrared laser, wherein e is amorphous. 2. A silicon or oxygen-free copper base material, a gold layer or a silver layer coated thereon, and a film thickness f formed by ion-assisted vapor deposition is f = λ cosec θ / 4n.
₁ (λ is an infrared wavelength, θ is a reflection angle in the layer, and n ₁ is a refractive index), a low-refractive-index layer of ZnSe (zinc selenide) or ZnS (zinc sulfide), and ion-assisted deposition. The film thickness e is e = λ cosec φ / 4n _h (λ is the infrared wavelength, φ is the reflection angle in the layer, n _h is the refractive index), and m pairs of high refractive index layers (m ≧ 2) are formed. A reflection mirror for an infrared laser, which is composed of an alternating laminated film provided on a gold layer or a silver layer in combination, and in which Ge of the high refractive index layer is amorphized. 3. On a silicon or oxygen-free copper substrate,
A gold layer or a silver layer is formed by sputtering or vapor deposition, and 0.05 μm to 0.15 μm is formed on the gold layer or the silver layer.
Of HfO ₂ (hafnium oxide) or Bi ₂ O ₃ (bismuth oxide) is formed by vapor deposition or sputtering, and an ion beam having an energy of 300 eV to 600 eV is applied for 5 minutes to 10 minutes to surface-treat the binder layer. , The film thickness f is f = λ cosec θ / 4n
ZnSe (zinc selenide) layer or ZnS, where _l (λ is the infrared wavelength, θ is the reflection angle in the layer, and n ₁ is the refractive index)
A (zinc sulfide) layer is formed on the binder layer by ion assisted vapor deposition, and the film thickness e is e = λ cosec φ / 4n.
_The Ge layer having _h (λ is an infrared wavelength, φ is a reflection angle in the layer, and n _h is a refractive index) is subjected to the above-mentioned Z
ZnSe (zinc selenide) layer or Zn having a film thickness f formed on the nSe (zinc selenide) layer or ZnS (zinc sulfide) layer and repeatedly formed by ion-assisted vapor deposition
A method of manufacturing a reflection mirror for infrared laser, characterized in that m sets (m ≧ 2) of alternating multi-layered films composed of an S (zinc sulfide) layer and a Ge layer having a film thickness e are provided on a binder layer. 4. On a silicon or oxygen free copper substrate,
A gold layer or a silver layer is formed by sputtering or vapor deposition, and the film thickness f is f = λ cosec θ / 4n ₁ (λ is an infrared wavelength, θ is a reflection angle in the layer, and n ₁ is a refractive index).
A Se (zinc selenide) layer or a ZnS (zinc sulfide) layer is formed on the gold layer or the silver layer by ion-assisted vapor deposition, and the film thickness e is e = λ cosec φ / 4n _h (λ is the infrared wavelength, φ is the layer A Ge layer having a reflection angle in which n _h is a refractive index) is formed on the ZnSe (zinc selenide) layer or ZnS (zinc sulfide) layer by ion-assisted vapor deposition, and then repeatedly formed by ion-assisted vapor deposition. Z of the film thickness f
m sets (m ≧ 2) of alternating multilayer films composed of an nSe (zinc selenide) layer or a ZnS (zinc sulfide) layer and a Ge layer having a film thickness e
Is provided on a gold layer or a silver layer, and a method for manufacturing a reflection mirror for infrared laser. 5. The film-forming process of ion-assisted vapor deposition of a ZnSe or ZnS film and a Ge film is carried out at a film-forming temperature of 200 ° C. to 270 ° C. A method for manufacturing a reflection mirror for infrared laser according to any one of 1. 6. When a ZnSe film, a ZnS film, and a Ge film are formed by ion-assisted vapor deposition, the ion beam acceleration energies are both 150 eV to 250 eV, and the ion beam current density is 10 to 10 for ZnSe or ZnS films. 30 μA / cm ² , ²⁰ to 4 for Ge film
It is 0 microA / cm < ² >, The manufacturing method of the reflection mirror for infrared lasers in any one of Claims 3-5 characterized by the above-mentioned.