JPH0240600A - multilayer reflector - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a multilayer film reflector used in the soft X-ray region, and particularly to a multilayer film reflector suitable for a soft X-ray microscope for biological observation. be.

[Prior Art] In the X-ray region, the refractive index of a substance is expressed as n=1-δ-ik (δ: real number) - (1), where both δ and δ are extremely small compared to 1. (The imaginary part of the refractive index represents absorption of X-rays.) Therefore, lenses that utilize refraction in the visible light region cannot be used.

Therefore, an optical system that utilizes reflection is used, but since the reflectance is very small at an incident angle close to perpendicular to the total reflection critical angle θC (approximately 5 degrees or less at a wavelength of 25 people), the amplitude reflectance of the interface By laminating many layers of high quality material combinations, a large number of reflective surfaces (for example, several hundred layers) are created, and the thickness of each layer is adjusted based on optical interference theory so that the phase of each reflected wave matches. A multilayer reflector is used.

To explain more specifically, a multilayer reflector is made by alternately laminating materials with a small difference in refractive index at the used X-ray wavelength and the refractive index of vacuum (=1) and materials with a large difference. Typical examples include combinations such as W (tungsten)/C (carbon) and Mo (molybdenum)/St (silicon).
It was formed using thin film forming techniques such as vacuum evaporation and CVD.

[Problems to be Solved by the Invention] By the way, the wavelength of X-rays used when performing biological observation with a soft X-ray microscope is in the region where the difference in absorption coefficient between protein and water is large, as shown in FIG. That is, the absorption edge (
23) and the carbon absorption edge (44) is used. (In order to be able to observe as thick a sample as possible, a wavelength of 25 nm near the absorption edge of oxygen, which has a small absorption coefficient, is more preferable.) However, in the soft X-ray region (wavelengths of 2.5~250 nm), conventional W (tungsten)/C (carbon) and Mo
(Molybdenum)/Si (Silicon) combination multilayer reflector can only obtain a low reflectance (about 10% at a wavelength of 25 people) and is not suitable for practical use. On the other hand, the combination of N1 (nickel)/Be (beryllium) has a high reflectance (30
However, beryllium powder is highly toxic and poses a serious risk to the human body during the manufacturing process.

The present invention was made in view of these problems, and an object of the present invention is to provide a multilayer reflector for soft X-rays that has a higher reflectance without using substances harmful to the human body. It is something.

[Means for Solving the Problems] In this invention, the refractive index in the soft X-ray region and the refractive index in vacuum (
=1) In a multilayer reflector formed by alternately laminating materials with a small difference in refractive index and materials with a large difference, tin, tin oxide, or a mixture of tin and tin oxide is used as the material with a small difference in refractive index. The above tasks have been achieved by this.

[Function] In order to obtain a high reflectance with a multilayer film reflector for X-rays, the refractive index (n = 1 - δ - 1k) of the two types of laminated materials must satisfy the following two conditions. It is known to be good. (
Shiraki et al., 1987 Autumn Conference of the Japan Society of Applied Physics, Lecture No. 19P-ZN-2) (1) In order to increase the reflectance at each interface, the difference in 6 between the two materials must be large.

(2) In order to reduce loss due to absorption and increase overall reflectance, k must be small for both materials.

Figure 5 shows the wavelengths of Sn, SnO, 5n02 for 25 people.
The values of δ and k of each substance of C51, Ni, and W9Mo are shown. Groups of substances with small δ (Sn, SnO, 5
(n02C, Si), tin, stannous oxide, and stannic oxide according to the present invention do not have much difference in the value of k indicating absorption compared to conventionally commonly used carbon and silicon. The value of δ is very small. That is, it is possible to increase the difference in δ between the two types of materials to be laminated, which is very advantageous in terms of increasing the reflectance of the interface (condition (I) above).
As a result, a much higher reflectance than before can be obtained.

On the other hand, substances with large δ include Re (rhenium), O8 (osmium), Ir (iridium), and pt (platinum), in addition to Ni, W, and Mo shown in the table of Figure 5.
, 8U (gold), Ta (tantalum), Iff (hafnium), Cu (copper), Go (cobalt), 7 (zinc)
.

Any suitable material such as Fe (iron) can be used, but as shown in the table of Fig. 5, nickel is preferably used because it has a very small value of k and can keep losses due to absorption low. or more preferable. That is, tin, tin oxide,
A multilayer reflector with the highest reflectance can be obtained by alternately laminating nickel and any one of the mixtures of tin and tin oxide.

[Example] <Example 1> As shown in FIG. 1, on a mirror-polished silicon substrate 3,
Using the RF magnetron sputtering method, nickel layers 2 with a thickness of 10 people and tin layers 1 with a thickness of 20 people were alternately laminated by 200 layers each (the number of layers is omitted in the figure) to form a multilayer reflector. Created.

Nickel and tin were used as the target materials, and argon was used as the sputtering gas during all film formation. In this multilayer reflector, the second layer and the top layer on the silicon substrate 3 side may be made of either a material with a small δ or a material with a large δ, but in order to increase the amplitude reflectance of the interface, It is more desirable to use a material with a large value of δ (in this example, nickel).

The reflectance of the multilayer mirror obtained as described above was determined at wavelength 25.
When measured using human X-rays, the results were as shown in Figure 2, and a high reflectance of 32% was obtained.

<Example 2> As in Example 1, a nickel layer with a thickness of 10 mm was formed on a silicon substrate by f magnetron sputtering.
A multilayer reflector was fabricated by alternately stacking 200 layers of tin oxide each having a thickness of 20 people.

Nickel and tin were used as the target materials, and argon was used as the sputtering gas when forming the nickel film, and a mixed gas of argon and oxygen was used when forming the tin oxide film. The tin oxide thin film thus obtained consisted of a mixture of stannous oxide and stannic oxide.

Next, when the reflectance of this multilayer mirror was measured using X-rays having a wavelength of 25, the results were as shown in FIG. 3, and the maximum reflectance was 29%.

Furthermore, during use, the temperature of the multilayer reflector may rise due to the absorption of X-rays, but the melting point of tin is 232°C, while the melting point of stannic oxide is as high as 1127°C. By increasing the degree of oxidation of the multilayer film reflecting mirror, it is possible to provide a predetermined heat resistance. The melting point of nickel is 1453°C, which is higher than that of stannic oxide. ) [Effects of the Invention As described above, the present invention uses a material selected from among tin, tin oxide, and a mixture of tin and tin oxide as a material having a small refractive index difference with that of a vacuum to form a multilayer reflective film. By constructing the mirror, it is possible to avoid using substances harmful to the human body such as beryllium.
It has an extremely excellent effect of providing high reflectance in the soft X-ray region.

Such a multilayer reflector is suitable for X-rays for biological observation (wavelength 23~
44 people) It can be applied to all optical equipment used in the soft X-ray region, such as microscopes, X-ray microscopes for other purposes, X-ray lithography, X-ray telescopes, and X-ray lasers, and its high reflectance As a result, the degree of freedom in designing the optical system can be increased, and the intensity of the light source can also be small, so that the size of the optical equipment can be reduced.

Furthermore, in such a multilayer reflective mirror, since the intensity of the light source can be reduced, the temperature rise due to absorption of X-rays can be kept low, and the prescribed heat resistance can be ensured by increasing the degree of oxidation of the tin oxide layer. It is also advantageous in terms of durability.

Furthermore, not using harmful substances eliminates the need for special safety equipment to ensure the safety of manufacturing workers, and can reduce manufacturing costs.

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional view of a multilayer reflector according to an embodiment of the present invention, FIG. 2 is a graph showing the reflectance of the multilayer reflector according to the embodiment shown in FIG. 1, and FIG. is a graph showing the reflectance of a multilayer film reflector according to another example, and FIG. 4 is a graph showing the absorption coefficients of water and protein in the soft X-ray region.
FIG. 5 is a table showing the refractive index of materials at a wavelength of 25. [Explanation of symbols of main parts] l...Tin layer 2...Nickel layer 3...Silicon substrate representative Patent attorney Masaru Sato Figure 2 Figure 5 Figure 4

Claims (2)

[Claims] (1) In a multilayer reflector formed by alternately laminating materials with a small difference in refractive index and a material with a large difference in refractive index in a soft X-ray region and a vacuum, the material with a small difference in refractive index may be tin or A multilayer reflector characterized by using tin oxide or a mixture of tin and tin oxide. (2) The multilayer film reflecting mirror according to claim 1, wherein nickel is used as the material having a large difference in refractive index.