JPH0797159B2 - Multi-layer mirror for soft X-ray / VUV - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention is directed to an optical device, and particularly to light having a wavelength of 2000 Å or less, which is called soft X-rays to vacuum ultraviolet rays. The present invention relates to a multilayer film reflecting mirror for soft X-rays and vacuum ultraviolet rays, which can be suitably used for incidence.

[Conventional technology]

Conventionally, for light on the shorter wavelength side than the region called vacuum ultraviolet, there is no reflector that has a high reflectance when incident at an angle perpendicular to or close to the surface, and it is close to normal incidence. At the incident angle, the reflectance was less than 1%. On the other hand, in the case of a grazing incidence reflecting mirror having a relatively high reflectance, it is necessary to adjust the incident angle to 1 ° or less or 2 to 3 ° from the mirror surface. Further, since the light is incident on the surface at a small angle, a very large shape is required even for a thin light beam, and its use is difficult and limited. In addition, there are few degrees of freedom in designing the optical system, and when manufacturing a reflecting mirror, it is often difficult to actually use it by polishing and holding it over a large area so as to have highly accurate flatness.

In recent years, with the development of vacuum deposition technology, multilayer film reflecting mirrors in which a large number of ultra-thin films are stacked in a multilayer structure have been manufactured, and it is possible to make a practical use with high reflectance by utilizing interference. .

By the way, in the X-ray and vacuum ultraviolet light regions, the refractive index of most substances is represented by a complex refractive index (n + ik, hereinafter referred to as the refractive index) having an imaginary part k representing absorption, and the real part n is approximately 1.0. (N = 1-δ, δ ~ 10 ^-1 -10 ^-3 , so the Fresnel reflectance at the boundary between the vacuum and the material thin film is very small, on the order of 0.1%. Even at the boundary, the reflectance does not exceed several% per single boundary surface.However, different materials are alternately laminated in a multi-layered structure, and the reflected light from each layer boundary is strengthened by interference, so that the whole multilayer film is formed. High reflectivity can be achieved by adopting a film thickness configuration that maximizes the reflectivity.In addition, select a combination of different materials that increases the difference in refractive index between adjacent layers, and Along with the film thickness configuration of Accordingly, it is known that reflection mirror at an angle of incidence close to normal incidence resulting a high reflectance can be realized.

[Problems to be solved by the invention]

However, these reflecting mirrors use a material having a large absorption, and they are often overheated by light irradiation during use to damage the film, and there is a drawback that they cannot be used stably for a long period of time in actual use. It was

In order to eliminate this defect, it has been proposed to use a high melting point metal as a high absorber, but the melting point of the metal alone is 2500 ° C.
There is a problem that the reflectance is not high when the metal is used even if there are many before and after, and even if there is more than 3000 ° C.

The present invention has been made in view of the above problems, and an object of the present invention is to eliminate the above-mentioned conventional drawbacks and to provide a reflecting mirror having excellent durability while maintaining high reflectance.

[Means for solving problems]

The above object of the present invention is to provide a multilayer film mirror for soft X-ray / vacuum ultraviolet ray having a multilayer thin film structure comprising alternating layers of a high absorption layer of soft X-ray / vacuum ultraviolet ray and a low absorption layer, wherein the high absorption layer is a transition layer. The low absorption layer comprises, as a main component, one or more of metal borides, carbides, suicides, nitrides or oxides, and the low absorption layer contains carbon, silicon, boron or beryllium alone or a compound thereof. This is achieved by a multilayer film reflecting mirror for soft X-rays / vacuum ultraviolet rays, which has at least one of them as a main component.

FIG. 1 is a schematic view of an embodiment of a multilayer film reflecting mirror for soft X-ray / vacuum ultraviolet ray according to the present invention.

The multilayer mirror for soft X-rays / vacuum ultraviolet rays according to the present invention shown in FIG. 1 has a first layer 2 which is a high absorption layer on a flat or curved substrate 1 which is sufficiently smooth compared to the wavelength used. , 4,6
, And the second layers 3, 5, 7, which are low absorption layers, are alternately laminated.

The superabsorbent layer of the present invention comprises, as a main component, one or more of transition metal borides, carbides, silicides, nitrides or oxides.

The transition metals used in the present invention are scandium (Sc) and titanium (T) which are elements having electron vacancies in 3d, 4d, and 5d orbits.
i), vanadium (V), chromium (Cr), iron (Fe), nickel (Ni), cobalt (Co), zirconium (Zr),
Niobium (Nb), Molybdenum (Mo), Technetium (T
c), ruthenium (Ru), rhodium (Rh), hafnium (Hf), tantalum (Ta), tungsten (W), rhenium (Re), osmium (Os), iridium (Ir), platinum (Pt), and 3d. , 4d, 5d are copper (Cu), palladium (Pd), silver (Ag), and gold (Au) whose orbits are filled with electrons.

Specific examples of the transition metal compound include tantalum boride, hafnium boride, tungsten boride and niobium boride as boride, and tantalum carbide, hafnium carbide, tungsten carbide and niobium carbide as carbides, and silicic acid. As the oxide, tantalum silicide, tungsten silicide, palladium silicide, etc., as the nitride, tantalum nitride, hafnium nitride, tungsten nitride, niobium nitride, etc., and as the oxide, tantalum oxynitride, etc. are preferably used. It

As described above, the high absorption layer of the present invention includes, for example, one of transition metal carbide, nitride and boride, and two or more substances such as tantalum nitride (TaN) and niobium nitride (NbN). It is needless to say that the above may be a material containing a) in any ratio.

The low absorption layer contains, as a main component, one or more of simple substances of carbon, silicon, boron or beryllium or their respective compounds, for example, compounds such as silicon carbide and boron carbide.

The film thickness d ₁ , d ₂ , ... of each layer is approximately 1/4 of the wavelength used.
The above is an alternate laminated film made of the same material, and the film thickness must satisfy the condition that all reflected lights at the boundaries between the layers interfere with each other, or the absorption loss by the absorber and the phase It is determined by satisfying any one of the conditions that the reduction in total reflectance is smaller when the reduction in reflectance due to the shift is compared. For example, at that time,
The film thickness may be the same for all layers of the same material, or may be different for each layer so that the reflectance is maximized and not necessarily equal.

As a laminated structure, it is desirable to select a material having a large difference between the refractive index of the final layer, which is the layer facing the air, and the refractive index of air. In order to form the final layer as described above, it is desirable to use the high absorption layer as the final product layer.

Further, the reflecting mirror of the present invention includes a two-layer structure consisting of one high-absorption layer and one low-absorption layer, but the larger the number of alternating layers, the more the reflectance increases, so the number of layers is 10 or more. It is preferable. However, if the number of layers is too large, the effect of absorption becomes noticeable, so if considering the ease of production, it is preferable to have about 200 layers.

Further, a protective layer made of a stable material with little absorption may be provided on the final layer.

In order to prepare the multilayer film reflecting mirror for soft X-ray / vacuum ultraviolet ray of the present invention, vacuum vapor deposition in ultrahigh vacuum is preferably used, but when a high melting point material is used, a sputtering method is also an effective means, Other methods such as resistance heating, CVD, and reactive sputtering for forming various thin films can be used.

The multilayer mirror for soft X-ray / vacuum UV of the present invention is usually a substrate of glass, fused silica, silicon single crystal, carbon silicide or the like, and its surface is sufficiently smooth as compared with the wavelength used. Created on a polished one.

〔Example〕

Hereinafter, the present invention will be described in more detail with reference to Examples of the present invention.

Example 1 Hafnium boride (HfB ₂ ) was used as a high absorption layer 2 on a silicon single crystal substrate 1 optically polished to have a surface accuracy of λ / 20 (λ = 6328Å) and a surface roughness of 10Å (rms value) to a thickness of 22.4Å, 41 layers of beryllium (Be) with a thickness of 33.5Å as the low absorption layer 3 (HfB ₂ : 21 layers, Be:
20 layers) were laminated. The final layer of the alternating layers was hafnium boride, and 10 (Å) carbon (C) was further laminated thereon as a protective film 10 to obtain a multilayer mirror for soft X-ray / vacuum ultraviolet ray according to the present invention.

Since hafnium boride has a high melting point of 3250 ° C., the above film formation was carried out by electron beam evaporation in an ultrahigh vacuum (1 × 10 ⁻⁷ Pa or less). Beryllium (Be) has a relatively low melting point (up to 1300 ℃), so it was vapor-deposited by the resistance heating method. The deposition rate was 0.2 Å / s for both materials. The protective layer was formed by the electron beam method.

This soft X-ray / vacuum ultraviolet multilayer mirror has a wavelength of 112.7Å
When the light was vertically incident, a reflectance of 31.3% was obtained. Also, the thickness of hafnium boride is 23.2Å and the thickness of beryllium is 3
A total of 41 layers were laminated with alternating layers of 6.2 Å, and a 10 Å carbon protective film was applied to obtain a similar multilayer mirror for soft X-ray / vacuum UV. When it was incident at an incident angle of 20 degrees from the normal, a reflectance of 34.3% was obtained.

Example 2 A tantalum nitride (TaN) layer having a thickness of 20.2 Å as the high absorption layer 2 and a silicon (Si) layer having a thickness of 40.8 Å as the low absorption layer 3 were 41 layers (TaN: 21 layers, S
i: 20 layers) were laminated. The last layer of the alternating layers is tantalum nitride as an absorber, and a carbon film 10 Å is formed on top of it as a protective film 10.
The layers were laminated to obtain a multilayer film reflecting mirror for soft X-ray / vacuum ultraviolet ray according to the present invention.

Tantalum nitride, which is a high-melting-point material, is used in ultra high vacuum (1 × 10 ^-7
The film was formed by electron beam evaporation at a pressure of less than Pa. In addition, low-absorbent silicon was also formed by the same method. The vapor deposition rate was 0.2Å / s for both materials.

When light of 124.0 Å was vertically incident on the multilayer mirror for soft X-ray / vacuum UV, a reflectance of 42.5% was obtained.

The thickness of the high absorption layer and the low absorption layer are 20.5Å and 44.0 respectively.
Incident angle from normal is 20 in total 41 layers alternately
When light with a wavelength of 124.0 Å was incident, a reflectance of 44.7% was obtained.

Example 3 Tungsten carbide (W ₂ C) was used as the high absorption layer 2 in a thickness of 21.1 Å as the high absorption layer 2 and silicon (Si) was used as the low absorption layer 3 in the thickness of 39.8 Å 41 layers (W) on the polished silicon substrate in the same manner as in Example 1. ₂ C: 21 layers,
Si: 20 layers) were laminated. The last of the alternating layers is a superabsorbent tungsten carbide. Further, a carbon film as a protective film 10 was laminated thereon to obtain a multilayer mirror for soft X-ray / vacuum ultraviolet ray according to the present invention.

Tungsten carbide, which is a high melting point material, is used in ultra high vacuum (1 x
The film was formed by electron beam evaporation at 10 ⁻⁷ Pa or less). In addition, low-absorbent silicon was also formed by the same method.
The vapor deposition rate was 0.2Å / s for both materials.

When light of 124.0 Å was vertically incident on the multilayer mirror for soft X-ray / vacuum UV, a reflectance of 42.8% was obtained.

Also, the thickness of the high absorption layer and the thickness of the low absorption layer are 21.7Å and 4 respectively.
When a total of 41 layers of 2.9Å were alternately laminated and a light of wavelength 124.0Å was incident at an incident angle of 20 degrees from the normal, a reflectance of 45.1% was obtained.

Reference Example A multilayer film for soft X-ray / vacuum ultraviolet ray was prepared by electron beam evaporation in the same manner as in Example 1 except that gold (Au) was used for the high absorption layer and carbon (C) was used for the low absorption layer. I got a reflector.

When this reflecting mirror was attached to a soft X-ray spectroscope using synchrotron orbital radiation (SR), and SR light was irradiated for a total of 5 hours, deterioration such as cracking and peeling of the film occurred.
Further, the multilayer film reflecting mirror for soft X-rays / vacuum ultraviolet rays of the present invention obtained in Examples 1, 2 and 3 was mounted on this apparatus and irradiated for the same time, but no damage occurred.

〔The invention's effect〕

As described above, the multilayer mirror for X-rays according to the present invention not only has a high reflectance for light in the soft X-ray / vacuum ultraviolet region, but also irradiates conventional synchrotron orbital radiation (SR). What caused significant damage in a short time due to
It has become possible to obtain durability for a sufficiently long time.

Especially, by combining a plurality of reflecting mirrors each having a flat surface or a curved surface, a reduction / enlargement optical system in the X-ray region, a reflecting mirror for a laser resonator in the soft X-ray / vacuum ultraviolet region, and a reflecting mirror structure. It is used as a new optical component in the area of X-ray optics, which has not existed in the past, such as a reflective dispersion element having a.

[Brief description of drawings]

FIG. 1 is a sectional view showing the principle of a multilayer film reflecting mirror. 1: substrate 2, 4: the first layer (high-absorption layer) 3, 5: the second layer (low-absorption layer) A: protective layer _{d 1, d 2, d 3} : thickness of the layer

Claims (1)

[Claims] 1. A multilayer mirror for soft X-ray / vacuum ultraviolet ray having a multi-layered thin film structure comprising alternating layers of a high absorption layer of soft X-ray / vacuum ultraviolet ray and a low absorption layer, wherein the high absorption layer is made of a transition metal. The low absorption layer contains, as a main component, one or more of boride, carbide, silicide, nitride or oxide, and the low absorption layer contains carbon, silicon, boron or beryllium alone or a compound thereof. A multilayer film reflecting mirror for soft X-rays and vacuum ultraviolet rays, which comprises one or more as a main component.