JPH09265005A - Mirror for excimer laser - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a mirror which exhibits high reflectivity to an excimer laser, is small in the change in the reflectivity by an incident angle between S polarized light and P polarized light and has a good adhesion property and laser resistance. SOLUTION: This mirror is constituted by successively laminating alternate layers 14 of dielectric films 12, metallic films 13, high-refractive index layers and low-refractive index layers on a substrate 11. The film constitution of the alternate layers is n1 L(n1 H.n2 L).n1 H.n1 L.n2 H (n3 L.n3 H)<j> .n3 L.n2 H. The relations of the optical film thickness are 2n1 L.d1 L=n1 H.d1 H-=n2 L.d2 L, 2n2 H.d2 H=n3 L.d3 L= n3 H.d3 H, n1 L.d1 L>n2 H.d2 H, where n1 L to n3 L denote the refractive indices of the low-refractive index layers; n1 H to n3 H denote the refractive indices of the high-refractive index layers; i, j denote 1, 2, 3...; n1 L.d1 L., n1 H.d1 H, n2 L.d2 L, n2 H.d2 H, n3 L.d3 L, n3 H.d3 H respectively denote the optical film thicknesses of the film constitution n1 L, n1 H, n2 L, n2 H, n3 L, n3 H.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention has a wide band in the ultraviolet region, a high reflectance, a reflection characteristic with little angle dependence, a strong laser resistance and a good adhesion between a substrate and a reflection film. The present invention relates to the excimer laser mirror shown.

[0002]

2. Description of the Related Art As conventional excimer laser mirrors, three types of structures are known. As a first example, a structure shown in FIG. 5 is known. This is an Al film 13 formed as a metal film on a substrate 11 such as glass,
A dielectric film 15 is coated on the metal Al film as a protective film for preventing deterioration such as oxidation of the metal Al film. FIG. 6 shows the spectral reflection characteristics of this excimer laser mirror, and FIG. 7 shows the incident angle characteristics when the laser wavelength is λ = 193.4 nm. This excimer laser mirror shows a uniform reflectance at an incident angle of θ = 0 to 40 ° at λ = 193.4 nm, but exhibits a reflectance of about 90% at most. Further, since the metal Al film easily absorbs the excimer laser light, the excimer resistance was low.

Further, since the adhesion between the substrate and the metal Al film is low and only one protective film is formed on the metal Al film, there is a problem that it is easily peeled off. As a second example, a structure shown in FIG. 8 is known. This is an alternating layer 14 of a high-refractive-index dielectric layer having an optical film thickness of λ / 4 (λ: design center wavelength) and a low-refractive-index dielectric film having an optical film thickness of λ / 4 on a substrate 11 such as glass. It has a laminated structure.

This dielectric high-reflectance film is 95% in the range of λ = 160 to 300 nm by changing the film thickness of each dielectric layer.
The reflection band above about 20 nm can be set arbitrarily. FIG. 9 shows the spectral reflection characteristics of this excimer laser mirror.
0 indicates the incident angle characteristic at the laser wavelength λ = 193.4 nm. This excimer laser mirror has a problem that the high reflection band of 95% or more is narrow at about 20 nm, and at the laser wavelength λ = 193.4 nm, the reflectance greatly decreases when the incident angle becomes larger than θ = 20 °. . Therefore, it was not suitable for use in the wavelength range of 20 nm or more and for incident angles of θ = ± 20 ° or more.

Therefore, as shown in FIG. 11, as a third example, which is considered to widen the high reflection band, is known. This has a structure in which two types of dielectric high reflection films 14 and 14 'having different center wavelengths are sequentially laminated on a substrate 11 such as glass. FIG. 12 shows the spectral reflection characteristics of this excimer laser mirror, and FIG. 13 shows the laser wavelength λ = 1.
The incident angle characteristics at 93.4 nm are shown. This excimer laser mirror shows a reflectance of 90% or more in the wavelength range of 180 nm to 210 nm, but the reflectance is temporarily reduced near the center of the reflection band (about 200 nm). In addition, at the laser wavelength λ = 193.4 nm, the incident angle is θ = 20 ° to 30 °.
The reflectance is temporarily reduced near ° and the incident angle is θ = 40 °
There has been a problem in that the larger the value is, the more easily the characteristic that the reflectance is significantly decreased. The cause of the temporary decrease in reflectance is due to the difference in reflectance between the P component and the S component depending on the wavelength and the incident angle.

Further, since this excimer laser mirror has a large number of film layers, it is easily affected by film absorption, scattering, film stress, etc., which causes a problem that the reflectance is limited and the film is easily peeled off. there were. Further, there is also a problem that the manufacturing cost is increased due to the large number of layers.

[0007]

SUMMARY OF THE INVENTION In the prior art as described above, a wavelength range of λ = 160 to 300 nm is set to an arbitrary value of about 40 nm.
High reflectivity of 95% or more for excimer lasers in the wavelength range of, excimer laser mirror with good adhesion and laser resistance, with little change in reflectivity between S-polarized light and P-polarized light depending on the incident angle. Was difficult to manufacture.

The present invention has been made to solve the above-mentioned conventional problems, and has a high reflectance of 95% or more for an excimer laser having an arbitrary wavelength range of about 40 nm in the range of λ = 160 to 300 nm. It is an object of the present invention to provide an excimer laser mirror that has a small change in reflectance between S-polarized light and P-polarized light depending on the incident angle, and has excellent adhesion and laser resistance.

[0009]

SUMMARY OF THE INVENTION The first aspect of the present invention is to provide an "excimer laser in which at least a dielectric film, a metal film, a high refractive index layer and a low refractive index layer are alternately laminated on a substrate. And a film structure of the alternating layers is n _1L (n _1H
・ N _2L ) ⁱ・ n _1H・ n _1L・ n _2H (n _3L・ n _3H ) ^j・ n _3L・
n _2H and the relationship of the optical film thickness is 2n _1L · d _1L = n _1H · d _1H = n _2L · d _2L 2n _2H · d _2H = n _3L · d _3L = n _3H · d _3H n _1L・ A mirror for an excimer laser, characterized in that d _1L > n _2H・ d _2H .

However, n _1L , n _2L and n _3L are the refractive index of the low refractive index layer, n _1H , n _2H and n _3H are the refractive index of the high refractive index layer and i, j
= 1, 2, 3 ..., n _1L · d _1L , n _1H · d _1H , n _2L ·
d _2L , n _2H · d _2H , n _3L · d _3L and n _3H · d _3H are the optical film thicknesses of the film constitutions n _1L , n _1H , n _2L , n _2H , n _3L and n _3H , respectively ( Claim 1) "is provided. In addition, the present invention secondly states that "the n _1L · d _1L is 0.12 to 0.15λ, the n _1H · d _1H and the n _2L · d _2L are 0.24 to 0.30λ,
N _2H · d _2H is 0.10 to 0.12λ, and n _3L · d is
3. The excimer laser mirror according to claim 1, wherein _3L and n _3H · d _3H are 0.20 to 0.24λ.

Where λ is the design center wavelength (claim 2).

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An excimer laser mirror according to an embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows an excimer laser mirror according to the first embodiment. The excimer laser mirror according to the present invention comprises a substrate 11, a dielectric film 12, and a metal film 1.
1. A pair of low refractive index layers sandwiching a first central layer composed of alternating layers of high refractive index layers and low refractive index layers, and a second central layer composed of alternating layers of high refractive index layers and low refractive index layers This is a configuration in which a pair of high refractive index layers 14 sandwiching the layers are sequentially laminated.

The dielectric film provided between the substrate and the metal film is
Any substance can be used as long as it is a substance that improves the adhesion between the substrate and the metal film. . High refractive index materials such as neodymium fluoride (NdF ₃ ), lanthanum fluoride (LaF ₃ ), gadolinium fluoride (GdF ₃ ), dysprosium fluoride (DyF ₃ ), aluminum oxide (Al ₂ O ₃ ), fluorine As low-refractive-index substances such as lead fluoride (PbF ₂ ) and mixed substances thereof, magnesium fluoride (MgF ₂ ), aluminum fluoride (AlF ₃ ), sodium fluoride (NaF), lithium fluoride (LiF), fluorine Calcium fluoride (CaF ₂ ), barium fluoride (BaF ₂ ), strontium fluoride (Sr
F ₂ ) and mixed substances thereof can be used.

As the substrate, various kinds of glass and crystal materials are used.
It is possible to use fluorite, magnesium fluoride, etc.
it can. Wide high reflection band by suppressing absorption of excimer laser
To obtain the area, the optical thickness is n _1L・ D> n_2H・ It is d
Is preferred. N in the film structure of the alternating layers_1L(N_1H・
n_2L)ⁱ・ N_1H・ N_1LThe part has a wavelength of about 200-220 nm.
Shooting, n_2H(N_3L・ N_3H)^j・ N_3L・ N_2HThe part is about 180
Reflects wavelengths of ~ 200 nm.

The substrate 11 is quartz glass that has been precisely polished, and the dielectric film 12 is a magnesium fluoride (MgF ₂ ) film having an optical film thickness of λ / 2 (λ = 193.4 nm). The dielectric film is not limited to a magnesium fluoride (MgF ₂ ) film with an optical film thickness of λ / 2 (λ = 193.4 nm), and a dielectric film or metal film sufficient to improve the adhesion between the substrate and the metal film is used. It suffices if there are films and their thickness.

This film is formed on the substrate 11 by a vacuum deposition method, a sputtering method or the like. The metal film 13 has a thickness of 1500
It is a metal Al film of about Å. The dielectric multilayer film 14 has the following structure. MgF ₂ (0.12-0.15λ) / [NdF ₃ (0.24-0.30λ) / MgF ₂ (0.24-0.30λ)] ⁹ / NdF ₃ (0.24
~ 0.30λ) MgF ₂ (0.12 ~ 0.15λ) / NdF ₃ (0.10 ~ 0.12λ) / [MgF ₂ (0.20 ~ 0.24λ) / NdF ₃ (0.20 ~ 0.24λ)] ⁹ / MgF ₂ (0.20
~ 0.24λ) NdF ₃ (0.10 ~ 0.12λ) Normally, when forming a metal Al film on a substrate, it is formed without heating to prevent oxidation of the metal Al film, and the protection is formed on the metal Al film. The film is also formed without heating.

When the dielectric multilayer film is formed, the film is formed by heating in order to increase the film strength. When a dielectric multilayer film is formed by heating on a metal Al film that has been formed without heating, the metal Al film is oxidized during heating of the substrate, and the adhesion between the dielectric multilayer film and the metal Al film decreases. To do.

Therefore, in the excimer laser mirror of the present invention, a metal Al film is formed while heating the substrate,
It is preferable to start the formation of the dielectric multilayer film immediately after the completion of the film formation. This can reduce the oxidation of the metal Al film over time. Further, as the protective film, a low refractive index layer having an optical film thickness that is an integral multiple of λ / 2 may be formed on the uppermost layer.

FIG. 2 shows the spectral reflection characteristic of θ = 0 ° in the excimer laser mirror of the first embodiment. From this spectral reflection characteristic, it can be seen that the reflectance is 95% or more in the reflection band of about 40 nm where λ = 175 to 215 nm. FIG. 3 shows an incident angle characteristic at λ = 193.4 nm in the excimer laser mirror according to the first embodiment. From this, in the case where the incident angle is in the range of θ = 0 to 45 °, S-polarized light and P
It can be seen that each of the polarization components can be maintained at 95% or more. In order to show such an incident angle characteristic, an excimer laser mirror having a small difference between the S-polarized component and the P-polarized component of the reflectance can be obtained when the incident angle used is oblique incidence. This means that when the excimer laser mirror of the present invention is used in a reflection optical system, the effect of reducing unevenness in brightness and darkness of an image formed by reflection is obtained.

[0020]

As described above, the excimer laser mirror of the present invention has a reflectance of 95% or more in the reflection band of about 40 nm of λ = 175 to 215 nm, and the incident angle at λ = 193.4 nm. In the range of θ = 0 to 45 °, both the S-polarized component and the P-polarized component of the reflectance can be maintained at 95% or more.

Further, by forming a dielectric film or a metal film between the substrate and the metal Al film, the adhesion between the substrate and the metal Al film can be enhanced and the film peeling can be made less likely to occur. If the mirror for excimer laser of the present invention is used as an optical element of a device that operates using ultraviolet light and excimer laser, further improvement in performance can be expected. The same effect can be obtained even if the substrate has a curvature such as a concave mirror. Therefore, if it is applied to an optical system where only conventional lenses have been used, the effects of higher performance and reduction in the number of lenses can be expected. . In particular, in the image formed by using the mirror for excimer laser of the present invention, unevenness in image formation due to a difference in polarization component of reflected light can be suppressed.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of an excimer laser mirror according to a first embodiment of the present invention.

FIG. 2 is a reflection characteristic diagram of the excimer laser mirror according to the first embodiment of the present invention.

FIG. 3 is an incident angle characteristic diagram at λ = 193.4 nm of the excimer laser mirror according to the first embodiment of the present invention.

FIG. 4 is a cross-sectional view of an excimer laser mirror having a concave substrate in the present invention.

FIG. 5 is a sectional view of a conventional excimer laser mirror as a first example.

FIG. 6 is a reflection characteristic diagram of a conventional excimer laser mirror as a first example.

FIG. 7 is an incident angle characteristic diagram at λ = 193.4 nm of a conventional excimer laser mirror as a first example.

FIG. 8 is a cross-sectional view of a conventional excimer laser mirror as a second example.

FIG. 9 is a reflection characteristic diagram of a conventional excimer laser mirror as a second example.

FIG. 10 is an incident angle characteristic diagram at λ = 193.4 nm of a conventional excimer laser mirror as a second example.

FIG. 11 is a sectional view of a conventional excimer laser mirror as a third example.

FIG. 12 is a reflection characteristic diagram of a conventional excimer laser mirror as a third example.

FIG. 13 is an incident angle characteristic diagram at λ = 193.4 nm of an excimer laser mirror as a third conventional example.

[Explanation of symbols]

 11, 11 '... Substrate 12, 15 ... Protective dielectric film 13 ... Metal Al film 14, 14' ... Dielectric multilayer film.

Claims (2)

[Claims] 1. An excimer laser mirror in which at least a dielectric film, a metal film, an alternating layer of a high refractive index layer and a low refractive index layer are sequentially laminated on a substrate, wherein the alternating layer has a film structure. Is n _1L (n _1H・ n _2L ) ⁱ・ n _1H・ n
_1L・ n _2H (n _3L・ n _3H ) ^j・ n _3L・ n _2H , and the relationship of optical film thickness is 2n _1L・ d _1L = n _1H・ d _1H = n _2L・ d _2L 2n _2H・An excimer laser mirror characterized in that d _2H = n _3L · d _3L = n _3H · d _3H n _1L · d _1L > n _2H · d _2H . Where n _1L , n _2L and n _3L are the refractive index of the low refractive index layer, n _1H and n
_2H and n _3H are the refractive indices of the high refractive index layer, i, j = 1, 2, 3 ·
_{··, n 1L · d 1L,} n 1H · d 1H, n 2L · d 2L, n 2H · d
_2H , n _3L · d _3L , n _3H · d _3H are the film constitutions n _1L ,
The optical film thicknesses of n _1H , n _2L , n _2H , n _3L , and n _3H . 2. The n _1L · d _1L is 0.12 to 0.15λ,
The n _1H · d _1H and the n _2L · d _2L are 0.24 to 0.30λ, the n _2H · d _2H is 0.10 to 0.12λ, and the n _{3L is}
The excimer laser mirror according to claim 1, wherein d _3L and n _3H d _3H are 0.20 to 0.24λ.
However, λ is the design center wavelength.