JPH07280999A - Multilayer film x-ray reflector - Google Patents

Abstract

PURPOSE:To provide a multilayer X-ray reflector whose board deformation caused by internal stress which leads to optical characteristic deterioration thereof is eliminated and reduced. CONSTITUTION:Thin films 4, 5, having internal stress, equal or approximately equal to a multilayer film are formed on the rear face of a board 3 in the multilayer film X-ray reflector composed of at least the board 3 and the multilayer film where a substance 2 with a large difference between refraction factor in a soft X-ray area and refraction factor in a vacuum and another substance with 1 with a small difference thereof are alternately multi-layered on the surface of the board 3.

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 for use in an X-ray reflection optical system in an X-ray telescope, an X-ray laser, an X-ray microscope, an X-ray lithography or various X-ray analyzers. Is.

[0002]

2. Description of the Related Art The refractive index of a substance in the wavelength range of X-rays is
n = 1-δ-iβ (δ and β are real numbers), and both δ and β are much smaller than 1 (the imaginary part β of the refractive index represents absorption of X-rays). That is, since the refractive index n is about 1, X-rays are hardly refracted. Therefore, a lens utilizing refraction such as the visible light wavelength region cannot be used in the X-ray wavelength region.

Therefore, an optical system utilizing reflection is used, but since the reflectance is very small at an incident angle closer to vertical than the critical angle for total reflection (about 5 ° or less at a wavelength of 25 Å), the amplitude reflectance of the interface is The thickness of each layer is based on the theory of optical interference by providing multiple reflective surfaces (for example, hundreds of layers) by stacking multiple layers of materials with high The X-ray multi-layered film reflecting mirror adjusted is used.

More specifically, the X-ray multilayer mirror has two types of substances on the substrate surface: a substance having a large difference between the refractive index at the used X-ray wavelength and a vacuum (= 1), and a substance having a small difference. Is obtained by alternately laminating a plurality of times to form a multilayer film, and as a typical example thereof, a combination of W / C, Mo / Si, etc. has been conventionally known. Moreover, the multilayer film is formed by a thin film forming technique such as sputtering, vacuum deposition, or CVD.

[0005]

However, when the above-mentioned multilayer film is formed on the surface of the substrate, stress is generated inside the multilayer film and the substrate is deformed, so that the optical characteristics of the X-ray multilayer film reflecting mirror are deteriorated. There was a problem. When a thin film is formed on a disk-shaped substrate, the internal stress σ is expressed as σ = E · b ² / {6 (1-ν) r · d}.
Here, E is the Young's modulus of the substrate, ν is the Poisson's ratio, b is the thickness of the substrate, d is the thickness of the thin film, and r is the radius of curvature when the substrate is uniformly deformed.

For example, when a fused silica substrate is used as the substrate, E / (1−ν) = 88.1 GPa. The thickness b of the substrate is set to 15 mm, and a multilayer film of 300 nm is formed on the surface of the substrate.
If formed, the radius of curvature r of the substrate deformation when the internal stress of the multilayer film is 1 GPa is 1.1 × 10 ⁴ m. If the substrate radius is 40 mm, the amount of protrusion or dent in the center of the substrate at this time is about 70 nm, which deteriorates the optical characteristics (aberration, etc.) of the X-ray multilayer film reflecting mirror.

The present invention has been made in view of such conventional problems, and eliminates or reduces the deformation of the substrate due to the internal stress of the multilayer film, which causes deterioration of the optical characteristics of the X-ray multilayer film reflecting mirror. An object is to provide a linear multilayer film reflecting mirror.

[0008]

Therefore, the first aspect of the present invention is to provide "at least a substrate, a substance having a large difference between the refractive index in the soft X-ray region and a vacuum refractive index on the substrate surface, and a small substance. In an X-ray multilayer reflecting mirror comprising a multilayer film in which a plurality of layers are alternately laminated, a thin film having an internal stress equal to or substantially equal to that of the multilayer film is formed on the back surface of the substrate. An X-ray multilayer mirror (claim 1) is provided.

A second aspect of the present invention is that "a thin film having an internal stress equal to or substantially equal to that of the multilayer film has the same structure as that of the multilayer film. (Claim 2) "is provided.

[0010]

The thin film (for preventing substrate deformation) formed on the back surface of the substrate 3 of the X-ray multilayer mirror according to the present invention is equal to or substantially equal to the multilayer film (for X-ray reflection) formed on the substrate surface. A single layer thin film or multilayer thin films 4 and 5 having internal stress can be used. As a method of equalizing or substantially equalizing the stress between the multilayer film (for X-ray reflection) formed on the front surface of the substrate 3 and the thin film (for preventing substrate deformation) formed on the back surface of the substrate, there is a method of producing an X-ray multilayer mirror. Prior to this, a multilayer film (for X-ray reflection) was formed on the front surface of the substrate for stress evaluation (a substrate that is easily deformed easily due to the internal stress of the thin film and the amount of deformation was easily evaluated), and a thin film (for preventing substrate deformation) on the back surface Then, the film forming conditions of the thin film (for preventing substrate deformation) such that the deformation amount of the substrate for stress evaluation becomes 0 or substantially 0 are found.

The substrate deformation amount for the stress evaluation is 0 or almost 0.
When a thin film (for preventing substrate deformation) is formed so that the following (when film forming conditions are set), the internal stress of the thin film should be equal or approximately equal to the internal stress of the multilayer film (for X-ray reflection). You can Such film forming conditions include, for example, thin film material, film thickness, film forming speed, film forming gas pressure, substrate temperature, and the like.
A suitable condition may be selected from these.

As the thin film (for preventing substrate deformation), it is preferable to use the same multilayer film as the multilayer film formed on the surface of the substrate (claim 2). In this case, it is preferable that the operation for finding the film forming conditions for the thin film (for preventing substrate deformation) in advance can be omitted. In addition, since the front and back substrates have the same multilayer film, both surfaces of the same substrate can be used as a multilayer reflector (simultaneously or with the front and back replaced), which is preferable.

Hereinafter, the present invention will be described in more detail by way of examples, but the present invention is not limited to these examples.

[0014]

[Embodiment 1] This embodiment will be described below with reference to FIG. Fused quartz substrate 3 by ion beam sputtering
Molybdenum layer 2 with a thickness of 2.5 nm and thickness of 5.0 n on the surface of
m silicon layers 1 are alternately formed, and one set is used for 5
A multilayer film for X-ray reflection was formed by stacking 0 sets.

Further, by the same method, 50 sets of the molybdenum layer 4 and the silicon layer 5 similar to the front face were laminated on the back surface of the substrate to form a multilayer film (for preventing substrate deformation) (in the figure, an intermediate layer). Is omitted). As described above, by forming the multilayer films having the same internal stress on the front and back surfaces of the substrate, the internal stress was canceled out, and the deformation of the substrate could be prevented. In addition, since the multilayer films on the front and back of the substrate are the same, both surfaces of the same substrate can be used as a multilayer film reflecting mirror (simultaneously on the front and back or with the front and back exchanged).

[0016]

Second Embodiment Hereinafter, this embodiment will be described with reference to FIG. As in Example 1, the film thickness was formed on the surface of the fused quartz substrate 3.
A 2.5 nm molybdenum layer 2 and a 5.0 nm-thickness silicon layer 1 are alternately formed, and 50 layers are laminated to form X layers.
A multilayer film for line reflection was formed.

A combination of substances having the same internal stress as that of the multilayer film (for X-ray reflection) but different from that of the multilayer film (for example, Mo / B ₄ C, Mo / BN, Mo / C, Mo).
/ SiC, W / C, Ni / C, Ni / SiO ₂ , NiC
r / C, NiCr / SiO ₂ , Cr / C, Cr / SiO
₂ ) A multilayer film (for preventing substrate deformation) was formed on the back surface of the substrate 3 using 6 and 7.

As a result, the internal stresses of both multilayer films were canceled out, and the deformation of the substrate could be prevented. Further, since the multilayer film formed on the back surface of the substrate is formed so that the wavelength range in which high reflectance is obtained is different from the wavelength range of the multilayer film formed on the front surface of the substrate, both surfaces of the same substrate are exposed to X-rays of different wavelength ranges. It could be used as a multilayer-film reflective mirror (simultaneously on the front and back or with the front and back replaced).

[0019]

According to the X-ray multilayer film reflecting mirror of the present invention, it is possible to eliminate or reduce the substrate deformation due to the internal stress of the multilayer film, which causes the deterioration of the optical characteristics of the reflecting mirror. Also,
There is also an advantage that the front and back of the substrate of the X-ray multilayer mirror can be used according to the purpose.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing an X-ray multilayer film reflecting mirror of Example 1.

FIG. 2 is a schematic cross-sectional view showing an X-ray multilayer reflecting mirror of Example 2.

[Explanation of symbols]

 1,5 Silicon layer 2,4 Molybdenum layer 3 Fused quartz substrate 6,71 1,2 and more

Claims (2)

[Claims] 1. At least a substrate and a soft X on the surface of the substrate.
An X-ray multilayer reflecting mirror comprising a multilayer film in which a substance having a large difference between the refractive index in a linear region and a vacuum refractive index and a substance having a small difference are alternately laminated, wherein: X formed by forming a thin film having an internal stress equal to or substantially equal to that of the film
Line multi-layer film reflector. 2. The X-ray multilayer mirror according to claim 1, wherein a thin film having an internal stress equal to or substantially equal to that of the multilayer film has the same structure as the multilayer film.