JPH0375600A - Multi layered film reflecting mirror - Google Patents

Abstract

PURPOSE:To enable prevention of oxidation of multi layered film without degrading the reflectance by providing a protection layer consisting of a silicon oxide, a tin oxide or a vanadium oxide. CONSTITUTION:On a mirror finished silicon based plate 3, a 10 Angstrom thick nickel and vanadium pentoxide are alternatively laminated to form 200 pairs of multilayered film and thereafter a silicon dioxide layer 1, for instance, is also formed on the surface of the multilayered film 2, as a protection layer. In this case, there is almost no degrading of reflectance even if the thickness of the layer 1 is reduced to 100 Angstrom and the thicker the layer 1 is, the wider the difference of reflectance is, compared by that of a carbon. After heat treatment under 500 deg.C, in an atmospheric condition and for one hour duration, the reflectance is measured again and the results tells that, for the layer 1 having thickness of 10 Angstrom , an X-ray is not reflected, for the layer 1 having thickness of 30Angstrom , the reflectance is degraded to some 1/2 and, for the layer 1 having thickness of more than 100 Angstrom , there is no change of the reflectance. Consequently, when the protection layer is set at a proper thickness with a stable oxide such as a silicon oxide, structural break down due to oxidation of the multilayered film, can be prevented and the film can be used under even much severe conditions.

Description

[Detailed Description of the Invention] [Field of Application in Industry A] The present invention is applicable to X-ray lithography, X-ray telescopes, X-ray microscopes, X-ray lasers, various X-ray analyzers, etc., and is used for reflective optical systems in the XM region. This invention relates to a multilayer film reflecting mirror.

[Prior Art] The refractive index of a substance in the X-ray region is expressed as n-δ-lβ (δ, β: positive real numbers), and δ
, β are both very small compared to 1, that is, the refractive index is close to 1, so X-rays are hardly refracted, and lenses that utilize refraction of light such as those in the visible light region cannot be used.

Therefore, an optical system is used to take advantage of reflection, but since the refractive index is close to 1, the C reflectance is very small, and most of the X-rays are transmitted or absorbed.We solve this problem. In order to achieve this, by stacking multiple layers of materials that have as large a difference in refractive index as possible in the wavelength range of the X-rays used, we create a large number of reflective surfaces that are interfaces between them, and the phase of the reflected wave from each interface can be adjusted. A multilayer reflector was developed in which the thickness of each layer was adjusted based on optical interference theory so that the A typical example of such a multilayer mirror is W.
(Tungsten)/C (Carbon) Multi FIII! J and Mo
(molybdenum)/SI (silicon) multi-FJIIi, etc. are known, and include sputtering, vacuum evaporation, CV
D (Chemical Vapor Deposit
ion gas phase reaction method).

By the way, in the above multilayer film reflecting mirror, at least one of its constituent materials is often metal, and there is a problem in that the metal oxidizes over time and the multilayer structure is destroyed. The oxidation reaction of this metal is
Since the temperature rise of the five-layer film due to absorption of X-rays rapidly accelerates the temperature rise, the multilayer film reflecting mirror has the disadvantage of having a short lifespan as an optical element.

In order to solve this problem, it has been proposed to form a protective layer on the surface of the multilayer film to prevent oxidation, and conventionally carbon has been used as the material for the protective layer. Specifically, forming an extremely thin carbon layer on the surface (for example, ^, M,
Hawryluk etal, 5PIE, Vol, 68
8. P. P., 81 (1986)), and if carbon is one of the constituents of the multilayer, carbon should be the top layer (e.g., E., Zieglar, etal, 5PI).
E, Vol, 68B.

PI! +3 (see 1g+18)).

[Problems to be Solved by the Invention] However, the above-mentioned conventional technology has the following two problems.

(1) In general, the X-ray absorption coefficient of a substance increases as the wavelength becomes longer, except near the absorption edge. Therefore, the wavelength C used
Therefore, absorption of X-rays by the protective layer increases, making it difficult to form a protective layer with a sufficient thickness to prevent oxidation without reducing reflectance.

(2) The heat resistance of the carbon film itself is not very high, and SOO℃
When heated to a certain degree, the carbon film oxidizes to carbon dioxide gas and disappears in an atmosphere containing oxygen.
Carbon films formed by methods such as CVD contain hydrogen, and when the temperature of the multilayer mirror increases, voids (holes) are formed due to the elimination of hydrogen, and the antioxidation effect cannot be expected.

This invention was made in view of this point, and allows for multi-F! without reducing the reflectance! The purpose is to provide a multilayer film reflector that can almost completely prevent oxidation of the film (and has excellent heat resistance and durability).

[i! Means for Solving the Problem] In the present invention, in a multilayer film reflecting mirror formed by alternately laminating materials having different refractive indexes in the X-ray wavelength region used,
By providing a protective layer made of silicon oxide, tin oxide, or vanadium oxide on the surface, the above-mentioned problem can be solved in a distant manner.

[Work] Silicon oxide constituting the protective layer in the present invention.

Tin oxide and vanadium oxide are very stable oxides, and their high antioxidation properties are maintained even if the temperature of the multilayer mirror increases due to irradiation with XIs.

It is preferable that the protective layer be thick to some extent from the viewpoint of anti-oxidation properties, but if it becomes too thick, the absorption of X-rays in the protective layer will increase and the reflectance of the multilayer mirror will decrease. . Therefore, it is desirable that the thickness of the protective layer be in the range of 10 to 3,000 layers, more preferably 100 to 500 layers, taking into consideration both antioxidant properties and reflectance. From Figure 6, which shows the Xll mass absorption coefficients of silicon and carbon, the longer the wavelength of the However, it can be seen that in the wavelength range between the absorption edge (wavelength 44), the absorption coefficient of silicon dioxide is smaller. This wavelength range (23-44 inputs)
This is the region where there is a large difference in the X-ray absorption coefficients of protein and water, and is an important region used in biological observation X-ray microscopes that obtain images by contrast due to the difference in transmittance (generally around 25λ near the oxygen absorption edge). The absorption coefficient of silicon dioxide is slightly larger on the shorter wavelength side than the above wavelength range, but as the wavelength becomes shorter, the absorption coefficient becomes sufficiently small. Slight differences in absorption coefficients (for example, less than 10 Å) do not pose a substantial problem.

Figure 1 is a cross-sectional view showing the structure of the multilayer reflector manufactured in this example. After forming 200 pairs of multilayer film 2 by alternately laminating nickel of 300 nm thick and vanadium pentoxide of 20 mm thickness, a silicon dioxide layer 1 is formed as an oxidation-preventing protective layer on the surface of the multilayer film to improve the reflection of the multilayer film. I made a mirror. In addition, for comparison, a multilayer film reflecting mirror was prepared in which a carbon layer was formed as a protective layer on a multilayer film formed in the same manner. At this time, the thickness of the protective layer was varied between O (no protective layer) and 3000 Å.

FIG. 3 is a graph showing the results of measuring the reflectance (ratio of !order diffraction peak intensity to incident X-ray intensity) using X-rays of 25 wavelengths for the multilayer reflector manufactured as described above. It is clear from Figure 0 that when silicon dioxide is used, there is almost no decrease in reflectance even if the thickness of the protective layer is increased to 100 mm, but when carbon is used, the decrease in reflectance is large. As the thickness of the protective layer increases, the difference in reflectance between silicon dioxide and carbon increases.

After measuring the reflectance, each multilayer reflector was heat-treated in the atmosphere at a temperature of 500° C. for 1 hour, and the reflectance was measured again. As a result, both those without a protective layer and those using carbon as a protective layer did not reflect any X-rays, and the structure of the multi-Fl film was destroyed.

On the other hand, for those using silicon dioxide as a protective layer, X-rays no longer reflected when the protective layer was thicker than 10 people, and when the thickness of the protective layer was 30 people, the reflectance decreased to about 1/2. No change in reflectance was observed. These results show that the multilayer film reflector of this example can be used under harsh conditions that could not be handled conventionally by appropriately setting the thickness of the protective layer.

In the above embodiments, the protective layer is made of silicon oxide, but the same oxidation prevention effect can be obtained even if the protective layer is made of tin oxide or vanadium oxide.

[Effects of the Invention] As described above, in the present invention, since a protective layer made of a specific stable oxide is provided on the surface of the multilayer film, destruction of the structure of the multilayer film due to oxidation is almost prevented. It can be completely prevented and the heat resistance and durability of the multilayer reflective mirror can be improved.

That is, according to the present invention, the reflectance does not decrease even when irradiated with high-intensity X-rays in an oxygen-containing atmosphere, and the multilayer film reflector can be used under harsh conditions that could not be used conventionally. becomes possible to use.

Among such multilayer film reflectors, those having a protective layer made of silicon oxide are particularly preferably used in X-ray microscopes for biological observation, and can maintain high reflectance even during long-term use.

[Brief explanation of drawings]

Fig. 1 is a cross-sectional view showing the structure of a multilayer reflector according to an embodiment of the present invention, Fig. 2 is a graph showing the X-ray absorption coefficients of silicon dioxide and carbon, and Fig. 3 is a graph showing the thickness of IIM and the multilayer film. It is a graph which shows the relationship of the reflectance of a reflecting mirror. [Explanation of symbols of main parts] 1: Silicon dioxide layer (protective layer) 2: Poly71111 3: Silicon substrate

Claims (1)

[Scope of Claims] A multilayer reflector formed by alternately laminating materials having different refractive indexes in the wavelength range of X-rays used, provided with a protective layer made of silicon oxide, tin oxide, or vanadium oxide on the surface. A multilayer reflector featuring: