JPH09318800A - Multilayer film mirror for x-ray - Google Patents

Abstract

PROBLEM TO BE SOLVED: To extremely reduce the coarseness of a thin film and improve the reflection factor of a multifilm layer by epitaxial-growing an Si alloy and Si by turns on a single crystal substrate and forming a superlattice thin film. SOLUTION: On a substrate 1 of a single crystal (Ge or Si), a very thin cryastal layer 2 of Si and a very thin crystal layer 3 of an Si alloy are epitaxial-growing by turns with a thin film forming method such as an MBE method. By this, tens of layers are piled to form a superlattice multilayer film. The heteroepitaxy on the single crystal substrate is limited by the kind of material and so multilayer film formation with combination of a variety of materials is not possble. However, an Si-Ge alloy thin film can realize heteroepitaxy for a substrate 1 of Si or Ge. By epitaxial-growing the mutlilayer film, thin film density can be made high and the reflection factor for X-ray is improved. Furthermore by constituting the multilayer film with a crystal thin film, the multilayer film is chemically stabilized, thermal diffusion at the mutlilayer film boundary is suppressed and so durability is improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an X-ray multilayer mirror, and more particularly to a crystal that is a superlattice multilayer film formed by alternately epitaxially growing an extremely thin crystal layer of Si alloy and an extremely thin crystal layer of Si. X composed of thin film
The present invention relates to a line multilayer film reflecting mirror.

[0002]

2. Description of the Related Art An X-ray multilayer mirror is one in which thin films made of materials having different refractive indexes are alternately laminated on a substrate, and X-rays are reflected by utilizing black diffraction by an artificial lattice of the thin films. is there. In particular, the multilayer mirror for hard X-rays and the multilayer mirror for high incidence angles have a very short cycle length of a few nm, which makes it difficult to form a continuous film due to island-shaped growth of a thin film. It was difficult to reduce the roughness of the thin film. Therefore, the obtained reflectance is very low compared to the theoretical value.

The multilayer mirror is usually composed of an amorphous thin film or a polycrystalline thin film. The multilayer-film reflective mirror having a wavelength of about 0.01 nm is formed by using, for example, W / B ₄ C as a material having different refractive indexes, and has an incident angle of 0.19.
The cycle length of the multilayer film is as thin as 1.5 nm even in degrees. In this wavelength region, it is difficult to form a continuous film for the above reasons, and it is difficult to increase the density of the thin film by the vapor deposition method. Therefore, the ion beam sputtering method, the RF sputtering method, or the ion beam assist method using these methods is used. It is manufactured by a film forming method. However, even if such a film forming method is used, it is difficult to form a continuous film, and it is difficult to manufacture a multi-layer film reflecting mirror having a high roughness because the thin film has a large roughness.

Further, the multilayer mirror for X-rays is composed of a combination of W, Mo and other heavy metal elements and B, C and other light elements, paying attention to the optical properties of the materials constituting the film. . However, if an attempt is made to form a metal thin film by this combination, the metal thin film is likely to become polycrystalline, which causes an increase in the roughness of the thin film. In addition, a reaction occurs between the metal layer and the light element layer at the interface between them, and a diffusion layer is formed to reduce the reflectance. Since the diffusion is also thermally promoted, there is a problem in the durability of the X-ray multilayer mirror.

[0005]

SUMMARY OF THE INVENTION The present invention provides an X-ray multilayer mirror which solves the above problems.

[0006]

An X-ray multi-layer film reflecting mirror constituted by a crystal thin film which is a super lattice multi-layer film made of Si alloy and Si was constructed. And Si alloy is Si-Ge,
An X-ray multilayer mirror made of Si-Fe or Si-Sn was constructed.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION An X-ray multilayer mirror is usually constructed by laminating an amorphous thin film or a polycrystalline thin film, but in the present invention, a Si alloy and Si are alternated on a single crystal substrate. Is epitaxially grown to form a superlattice thin film as a whole, and this is used as an X-ray multilayer mirror.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to FIGS. This invention uses a superlattice multilayer film composed of a Si alloy thin film and a Si thin film as an X-ray multilayer film reflecting mirror. FIG. 1 showing the structure of an X-ray multilayer mirror
, Single crystal Ge substrate or single crystal Si
An extremely thin crystalline layer 2 of Si is formed on the substrate 1 by a MBE method, a CVD method, or another thin film forming method of Si alloy and Si.
And a very thin crystal layer 3 of Si alloy are alternately epitaxially grown and a total of several tens of layers are laminated to form a superlattice multilayer film. As a result, the wavelength is 0.01 nm,
A multilayer-film reflective mirror having an incident angle of 0.19 degrees is formed.

In FIG. 2, the roughness of the thin film on the Si substrate 1 is rm.
shows the reflectivity of the multilayer mirror of the present invention that Si _{0. 5} Ge _0.5 / Si 51 layer laminate was formed by a thin film of 0nm with s by the solid line, W / B ₄ multilayer mirror C was 51 layer laminate The reflectance is shown by the dotted line. If the roughness of the thin film is a 0nm in rms, who W / B ₄ C multilayer reflector is the reflectance as compared to the multilayer reflector is higher of the present invention, the W / B ₄ C multilayer film The period length is as thin as 1.5 nm, which makes it difficult to form a continuous film or a flat film.

FIG. 3 shows a wavelength of 0.01 nm and an incident angle of 0.19.
It is a figure which shows the reflectance of the X-ray multilayer-film reflective mirror formed for the purpose, and the dotted line is W / B of 0.5 nm in roughness of a thin film at rms.
_The theoretical reflectance of 51 layers of ₄ C is shown. The solid line shows the thin film roughness rms of 0 nm Si _0.5 Ge _0.5 / Si.
The theoretical reflectance of a stack of 51 layers is shown. W / B ₄ C
When the roughness of the thin film of the multilayer film is 0.5 nm in rms, the reflectance is significantly reduced. On the other hand, Si _0.5 Ge _0.5
Since the / Si multilayer film can sufficiently reduce the roughness of the thin film, the reflectance is higher than that of the W / B ₄ C multilayer film.

Heteroepitaxy on a single crystal substrate is limited in the kinds of materials, and it is impossible to form a multilayer film of a combination of various materials. However, a Si-Ge alloy thin film is made of Si.
Heteroepitaxy can be realized on a substrate or a Ge substrate. Further, the Si-Ge thin film has a limit on the epitaxial critical film thickness due to the composition ratio of Ge,
Since the X-ray multilayer mirror has a period length of about several nm, there is almost no problem with epitaxy. In general, the smaller the composition ratio of Ge, the easier the epitaxy. However, even if the composition ratio of Ge is changed, there is almost no difference in the reflectance at this wavelength, as shown in FIG. The phase diagram of Si-Ge is shown in Fig. 5. Since this is a completely solid solution substance, Ge
The composition ratio of can be changed to some extent freely, and
A multilayer-film reflective mirror can be easily manufactured.

In the above description, S is used as the Si alloy.
i-Ge is adopted, but Si-Fe, Si-Sn
Can also realize heteroepitaxy for a Si substrate or a Ge substrate. The density of the multilayer thin film obtained by using a crystalline thin film is equivalent to that of the bulk, and the bonds between atoms are stronger than amorphous and polycrystalline, so that diffusion between layers is unlikely to occur and it is thermally stable. is there. Therefore, the durability is also improved as compared with the conventional multi-layer film reflecting mirror in which the heavy metal element and the light element are alternately laminated.

[0013]

As described above, according to the present invention, Si alloys and Si are alternately epitaxially grown on a single crystal substrate to form a superlattice thin film as a whole, which is used as an X-ray multilayer mirror. However, a continuous film can be formed even with a thin film having a thickness of several nm or less. Therefore, the roughness of the thin film can be made as small as possible, which leads to the improvement of the reflectance of the multilayer film.

The density of the thin film can be increased by epitaxially growing the multi-layer film, which leads to improvement of the X-ray reflectance. Moreover, since a continuous film can be manufactured in an extremely thin region, a multilayer film reflecting mirror for hard X-rays and high incident angles can be manufactured. Furthermore, since the multilayer film is chemically stable by forming the multilayer film with the crystalline thin film, it is possible to suppress the diffusion and thermal diffusion at the interface of the multilayer film. Leads to improvement.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of an X-ray multilayer mirror.

FIG. 2 is a diagram showing the reflectance of an X-ray multilayer mirror, where the dotted line shows the theoretical reflectance of 51 layers of 0 / nm W / B ₄ C having a roughness of rms, and the solid line shows the thin film. Shows the theoretical reflectance of 51 layers of Si _0.5 Ge _0.5 / Si having a roughness of rms of 0 nm.

FIG. 3 is a diagram showing a reflectance of an X-ray multilayer film reflecting mirror, and a dotted line shows a theoretical reflectance of 51 layers of W / B ₄ C having a roughness of rms of 0.5 nm and 0.5 nm, and a solid line. Is a thin film with a roughness of rms of 0 nm of Si _0.5 Ge _0.5 / Si 51
The theoretical reflectance of the layered product is shown.

FIG. 4 is a graph showing the reflectivity of an X-ray multilayer mirror, where the dotted line shows Si _0.5 Ge _0.5 / 0 when the thin film has a roughness of rms of 0 nm.
The theoretical reflectance of a stack of 51 layers of Si is shown. The solid line is the Si _0.2 Ge _0.8 / Si film whose roughness is 0 nm in rms.
The theoretical reflectance of a stack of 51 layers is shown.

FIG. 5 is a state diagram of Si-Ge.

Claims (2)

[Claims] 1. An X-ray multilayer mirror comprising a crystalline thin film which is a superlattice multilayer film made of Si alloy and Si. 2. The X-ray multilayer film reflecting mirror according to claim 1, wherein the Si alloy is Si—Ge, Si—Fe, or Si—Sn.