JPH0219800A - Manufacture of multi-layer film reflecting mirror and multi-layer film reflecting mirror - 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 reflecting mirror used in reflective optical systems in the X-ray region such as X-ray lithography, X-ray microscopes, X-ray telescopes, and X-ray lasers. It is something.

[Prior Art] The refractive index of a substance in the X-ray region is expressed as n = 1-δ-ik (δ: real number) (1), where both δ and δ are very small compared to 1, that is, Since the refractive index is close to 1 and X-rays have the property of traveling straight through materials, lenses that utilize refraction such as in the visible light region cannot be used. Therefore, an optical system that uses reflection is used, but the reflectance is very small at an incident angle smaller than the total reflection critical angle θC (maximum 6 degrees at a wavelength of 25).
A multilayer reflective mirror with a large number of reflective surfaces is used.

Such a multilayer film reflecting mirror can be obtained by alternately stacking materials with a large value of δ and materials with a small value of δ in formula (1), and a typical combination thereof is tungsten (hereinafter referred to as W). Multilayer films using carbon (hereinafter referred to as C: small δ) have been known for a long time, and can be produced using sputtering, vacuum evaporation, CVD (Chemical Vapor
Deposition (vapor phase chemical reaction method), etc. (Reference: T.

Barbee and J, H, Underwood,
Opt, Commun, 48.3 (1983) PI6
1 to 166 in detail. ) As is already well known, the principles of multilayer reflective mirrors are as follows: (1) If there are interfaces with different refractive indexes, reflection will occur there, so create as many interfaces as possible to increase reflection; (2) Optical film thickness is set so that the reflected light from the first interface and the reflected light from the next interface are in phase, thereby causing and intensifying optical interference. There are two points.

[Problem to be solved by the invention] However, in the conventional technology, the actual measured value of the reflection qI ratio of the manufactured multilayer mirror was much lower than the reflectance theoretically calculated at the design stage, and There has been a problem in that certain characteristics cannot be achieved with devices such as exposure equipment and microscopes.

The present invention has been made in view of this point, and it is an object of the present invention to provide a W/C multilayer I-reflection mirror that can obtain a high reflectance close to the design value, and a method for manufacturing the same.

[Means for Solving the Problems] In the present invention, a laminate in which zero layers and amorphous W layers are alternately stacked in a non-oxidizing atmosphere such as a vacuum or an inert gas, The above object is achieved by crystallizing all or part of the W layer through heat treatment.

[Function] In the conventional W/C multilayer film reflecting mirror, it is presumed that the following two points are the main reasons why a reflectance lower than the design value is obtained.

(1) Due to the roughness of the interface of the multilayer film, there is loss due to light scattering.

(2) Since the density of the W layer, which is a thin film, is lower than that of the bulk, the value of δ is smaller than that of the bulk.

That is, W is deposited by sputtering, vacuum deposition, CVD, etc.
/C When forming a multilayer film reflector, if the substrate temperature is set to a high temperature and the W layer is made polycrystalline, surface roughness increases due to crystal grain growth during film formation, and as a result, the surface roughness increases due to light scattering. It is thought that losses will be large. Conversely, when a W layer is formed under conditions that do not crystallize, the interface roughness is small because there are no crystal grains, but it is thought that many atomic-order vacancies are scattered in the W thin film, resulting in a polycrystalline density. In other words, δ becomes smaller than in the case of .

Therefore, in the present invention, first, a W/C multilayer film is formed under conditions in which the W layer does not crystallize.

At this stage, the density of the W layer is smaller than that of the polycrystalline layer, that is, the value of δ is small, so the reflectance is quite low. However, since there are no crystal grains, the interface between the W layer and the 0 layer is flat.

Note that the 0 layer does not necessarily have to be in an amorphous state (low density state), although it is preferable to do so.

Next, when this is heat-treated in a non-oxidizing atmosphere such as a vacuum or an inert gas at a temperature of about 500 to 1000°C, preferably about 900°C, the W layer is crystallized. At this time, since the W layer is sandwiched between the top and bottom by the 0 layer,
Large crystal grains in the W layer are difficult to grow, become extremely fine microcrystals, and the roughness of the interface hardly increases. Then, by microcrystallization, the vacancies in the W thin film disappear, and δ of the dense W layer approaches the value of the bulk.

That is, in the W/C multilayer film according to the present invention, since the interface of the W layer is smoother than in the past, there is less light scattering at the interface, and since the W layer is crystallized, δ close to a baffle. Therefore, a high reflectance close to the design value can be obtained.

In addition, the 0 layer is generally difficult to crystallize, and is usually amorphous or amorphous containing graphite structure microcrystals,
The surface roughness is small, and δ is also a small value. In such a multilayer film, since it is better for the 0 layer to have a smaller δ, there is no particular problem.

[Example] A W layer 2 with a thickness of about 20 and a 0 layer 3 with a thickness of about 20 are formed on a Si substrate 1 by an RF magnetron sputtering method.
By alternately forming 20 layers each, a multilayer X-ray reflecting mirror with a total film thickness of about 800 layers as shown in FIG. 1 was created. (The number of layers is omitted in the figure. In this case, S
Crystallization of the W layer was prevented by keeping the temperature of the i-substrate 1 at room temperature.

Next, the multilayer film reflector produced in this way was heat treated in vacuum at temperatures of 600°C, 800°C, and 900°C for 1 hour, and then The reflectance of Bragg reflection was measured and compared with that without heat treatment. The results are shown in FIG. As shown in the figure, the reflectance of the sample without heat treatment is 30*, but the reflectance of the sample with heat treatment is clearly improved. The higher the processing temperature, the better the reflectance, 900! The reflectance at 900℃ is 3996.
This is an increase of about 3096 compared to that without heat treatment.

When the cross-sections of these multilayer reflectors were observed using a TEM (transmission electron microscope), it was found that both the W and C layers were amorphous in those that were not heat-treated, and that the zero layer was amorphous in those that were heat-treated at 900°C. Although it remained amorphous, W! Inside, microcrystals with a grain size of 10 Å or less were observed together with an amorphous phase, and the amorphous phase and microcrystalline phase were mixed in the same ratio. In order to increase δ of the W layer, preferably the proportion of the dense microcrystalline phase is as high as possible, and ideally, it is desirable that the entire W layer is a microcrystalline phase.

As a comparative example, a multilayer film reflector was formed by heating the substrate temperature to about 200°C to form a polycrystalline 4-layer W layer, and then stacking a 0 layer on top of it. When the reflectance was similarly measured, only a reflectance of about 30* was obtained. As mentioned above, this is the W layer and 0
This is thought to be due to the rough interface between the layers, which increases the loss due to light scattering.

In addition, in this example, the multilayer film reflecting mirror was formed by battering, but vacuum deposition, CVD, etc. It goes without saying that similar effects can be obtained by the film forming method of . The heat treatment process may be performed in an inert gas instead of in a vacuum, but if performed in the atmosphere, C will disappear as CO2 and W will become WO2.
It must be carried out in a non-oxidizing atmosphere.

[Effects of the Invention] As described above, according to the present invention, W in the 0 layer and in the amorphous state
Since the W layer is crystallized by heat treatment after laminating the two layers, it is possible to achieve both flatness of the interface between the W layer and the zero layer and densification of the W layer, resulting in a higher reflectance than conventional ones. or can be obtained.

Further, since the W/C multilayer film reflecting mirror according to the present invention has undergone a high temperature thermal history in a heat treatment process, its heat resistance is also improved. When such a multilayer film reflecting mirror is used in a vacuum, there is no structural change up to the heat treatment temperature (for example, 900° C.), and even if high-intensity X-rays are irradiated, the mirror will not be destroyed due to the temperature increase due to its absorption.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of a W/C multilayer film reflector according to the present invention;
FIG. 2 is a graph showing the relationship between heat treatment temperature and reflectance. [Explanation of symbols of main parts] j...Si substrate, 2...W layer, 3...C layer Attorney Masatoshi Sato, patent attorney

Claims (2)

[Claims] (1) A laminate in which carbon layers and amorphous tungsten layers are alternately stacked is heat-treated in a non-oxidizing atmosphere to crystallize all or part of the tungsten layers. A method for manufacturing a multilayer reflective mirror. (2) In a multilayer reflector in which carbon layers and tungsten layers are alternately laminated, the tungsten layer is a microcrystalline material with a grain size of 10 Å or less, or a microcrystalline material and an amorphous material with a grain size of 10 angstroms or less. A multilayer film reflector characterized by consisting of a phase.