JPH0372298A - Manufacture of multilayer film reflecting mirror - Google Patents

Abstract

PURPOSE:To make it possible to secure a high reflectance on the whole reflecting surface of a reflector by a method wherein a multilayer film formed on a curved surface is subjected to heat treatment for a heating time being different for each place and thereby a film thickness cycle is varied so that the condition of Bragg diffraction be met in each place. CONSTITUTION:A base 1 of which a reflecting surface is a spheroid is formed. The base 1 is disposed so that a sputtering target 4 and the rotational axis 6 of the spheroid are parallel to each other and is swung around an axis 7 being parallel to the axis 6, and substances 2 and 3 being different in a difference from a refractive index in vacuum are deposited in layers alternately so that a film thickness distribution in the direction intersecting the axis 6 perpendicularly be uniform. Subsequently, irreversible heat treatment is conducted for a heting time being different for each place, since a variation in a film thickness cycle is dependent on a temperature and the heating time, and thereby a control is made so that the condition of Bragg diffraction be met in each place of a curved surface.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a multilayer optical system used in a reflective optical system in the X-ray region in X-ray lithography, X-ray microscopes, X-ray telescopes, various ffI This relates to a membrane reflector.

[Prior art] The refractive index of a substance in the X-ray region is expressed as n = 1-δ-4k (δ: real number) (1), and δ is very small compared to 1. . In other words, the refractive index is close to 1, and X-rays are hardly refracted.
Lenses that utilize refraction such as those in the visible light region cannot be used. Therefore, an optical system using reflection is used, but such a reflecting mirror has a critical angle of total reflection θC (wavelength 25 for 6 people).
°) Below, there are total reflection mirrors used for oblique incidence, and multilayer film reflection mirrors with a large number of reflection surfaces. The former has disadvantages in that the dimensions of the optical system become large due to oblique incidence and large aberrations, and in this respect a multilayer film reflecting mirror is superior.

A multilayer film reflector is one in which materials with large and small δ in equation (1) are alternately laminated in the wavelength range used, and the phases of the reflected waves at each interface are aligned to obtain a high reflectance as a whole. , tungsten (W)/carbon (C) and molybdenum (
Combinations such as MO)/silicon (Si) have been known. Such a multilayer film reflector can be manufactured by sputtering, vacuum deposition, CVD (Chemical Vapor
For example, when used for focusing X-rays, the multilayer film has a spherical surface, an ellipsoid of revolution, a paraboloid of revolution,
It is formed on a base material having a curved surface shape such as a hyperboloid of rotation.

[Problem to be solved by the invention] In the conventional technology as described above, the period d of the thickness of the multilayer film
In order to align the phases of the reflected waves at each interface, (2)
The Bragg diffraction condition of the formula must be satisfied.

2dSinθ=nλ (2) where θ is the incident angle, λ is the wavelength of the X-ray, and n is an integer and the order of diffraction.

Figure 2 shows an example of a reflecting mirror using an ellipsoid of revolution. When a point light source is placed at one focal point fl of the ellipse, the light emitted from it is condensed to the other focal point f2. At this time, the incident angle θ0 at different positions (p+, Q+) (P2.Q2) on the reflecting surface
．． θ2 are not equal.

Therefore, in order to satisfy Bragg's condition (2) at each location, it is necessary to change the period d of the multilayer film at each location. This also applies to general curved surfaces other than spheroidal surfaces.

Here, changing the period of the multilayer film depending on each location on the curved surface is disclosed in Japanese Patent Laid-Open No. 60-98399. However, this publication does not describe any means for forming a multilayer film in which the film thickness period differs from place to place, and if I had to guess, it would be considered to utilize the film thickness distribution that occurs during film formation.

However, it is very difficult to arbitrarily control the film thickness distribution during film formation, and it is possible to create a film thickness distribution that does not satisfy Bragg's diffraction conditions at each location on the curved surface depending on the film formation conditions. However, the yield is extremely poor and it is virtually impossible. For this reason, conventional multilayer film reflecting mirrors have the problem of being able to satisfy the Bragg condition only in a small portion of the reflecting surface, resulting in very poor efficiency.

The present invention was developed in view of these conventional problems, and it is an object of the present invention to provide a method for manufacturing a multilayer reflector that satisfies Bragg's diffraction conditions at each location on a curved surface.

[Means for Solving the Problems] In the present invention, after forming a multilayer film with a substantially uniform film thickness period on a curved surface, the film thickness period of the multilayer film is changed by processing with different heating times for each location. The above-mentioned problem is achieved by changing the position at each location so as to satisfy the X-ray Bragg diffraction conditions.

[Function] While conducting experiments to evaluate the heat resistance of multilayer reflective mirrors, the present inventors discovered a phenomenon in which heat treatment increases the film thickness period d of the multilayer film and also increases the reflectance. . Figure 3 is a graph showing the relationship between the heat treatment temperature and the rate of increase in the film thickness period d when a W/C multilayer film reflector is heat treated in vacuum. The period d of the multilayer film gradually increases (several percent), and even at the same temperature, the rate of increase in the period d differs depending on the heating time (third
In the example shown in the figure, it can be seen that the increase rate differs by about 3 or more between the heating time of 1 hour and the heating time of 10 hours. This phenomenon of increase in film thickness period due to heat treatment is irreversible, and observation of a TEM (transmission electron microscope) image of a cross section of the multilayer film reveals that microcrystalization has occurred in the W layer after heat treatment. I understand.

Therefore, as a result of intensive studies, the present inventors have made it possible to control the film thickness distribution of a multilayer film formed on a curved surface by utilizing the phenomenon of irreversible increase in film thickness due to heat treatment. We have achieved this.

That is, since the change in the film thickness period d is dependent on temperature and heating time as shown in Figure 3, it is possible to change the film thickness period at each location by heat-treating at a different temperature for each location. In addition, by changing the heating time for each location, the thickness distribution of the multilayer film can be controlled so that the Bragg diffraction conditions are satisfied at each location on the curved surface. The film thickness distribution in the present invention may be controlled by keeping the heating temperature almost constant and changing only the heating time from place to place, or by changing the heating time from place to place.
Depending on the case, both the heating time and the heating temperature may be changed.

FIG. 1 is a schematic cross-sectional view of a multilayer reflective mirror obtained by the manufacturing method according to the present invention. In the figure, on the curved surface of a base material 1, a material 2 such as tungsten, which has a large difference in refractive index from the vacuum, and a material 3, such as carbon, which has a small difference in the refractive index from the vacuum, are alternately laminated. , substances 2 and 3
The film thickness period is controlled so that the Bragg diffraction conditions are satisfied at each location on the curved surface by heat treatment with different heating times for each location (in this case, the center of the cross section is thicker and the edges are thinner). have been). At this time, as the period d changes, the crystallization state of the multilayer film also changes, and the longer the heat treatment is performed, the more microcrystallization progresses.

Note that the method of heat-treating the multilayer film in the present invention is not particularly limited, and a heat source such as a heater may be placed at a predetermined position, or a laser beam may be focused into a spot and scanned at each location. This may be carried out by irradiating the surface of the multilayer film while changing the speed.

[Example] Example=1 First, using glass, Figure 4 (Figure a is a plan view).

As shown in FIG. 1 (FIG. 1 is a side view in the long axis direction) and FIG. C is a side view in the short axis direction (Fig. The reflective surface of this base material 1 has a long sleeve radius of 5
It was formed by cutting a part of an ellipsoid of revolution, which is created by rotating an ellipse with a diameter of 0 mm and a minor axis radius of 20+nm around the major axis as the center of rotation, with a cross section of an ellipse with a major axis radius of 20 mm and a minor axis radius of 8 mm. It is something.

In such a reflective surface, when a point light source is placed at one focal point f of the spheroid as shown in Figure 4, the light emitted from it is focused at the other focal point f2. be illuminated. Here, the incident angle is θ, = 23 at the center of the reflecting surface.
．． 8', 02 = 25.5° at the end in the long axis direction, so if the wavelength of the X-ray used is 25λ, the film thickness period d of the multilayer film that satisfies Bragg's condition is the center of the reflective surface. Then, d,=31.3, is 29.1 at the end in the longitudinal direction, and the difference in film thickness is 7.5.

Next, 50 13-thick W layers and 16-thick 0 layers were alternately laminated on the reflective surface by RF magnetron sputtering. As shown in FIG. 5, the base material 1 is arranged so that the sputtering target 4 and the rotation axis 6 of the spheroid are parallel to each other, and during film formation, the sputtering target 4 is parallel to the rotation axis 6! The base material 1 was oscillated around X1lI17 so that the film thickness distribution in the direction orthogonal to the rotation center axis 6 was made uniform.

On the other hand, in the long sleeve direction of the ellipse, since the slope of the plane is different, there is a difference in film thickness between the ends and the center. The difference in film thickness at this time is 1.5 zero between the center of the reflective surface and the ends in the long axis direction. Therefore, in order to satisfy Bragg's condition at all positions of the reflecting surface, the maximum must be 7.5*-1.5%F=6. Film thickness period d
will have to be adjusted. The base material 1 and its holding jig are configured so that they can be moved onto different targets 4 in a vacuum, and by moving them alternately onto W and C targets, the W layer and the 0 layer are separated. Laminated in sequence.

Next, the multilayer film reflecting mirror thus produced was heat-treated using an apparatus as shown in FIG. As shown in the figure, a strip heater 8 made of tungsten was placed close to the reflective surface 9 of the multilayer mirror in parallel to the minor axis of the ellipse, which is the cross section of the spheroidal surface. The strip heater 8 is movable in the long direction of the ellipse, and by moving the heater 8 while energizing it, the entire surface of the reflective surface 9 can be heated.

At this time, by changing the moving speed of the strip heater 8, heat treatment can be performed for each location on the reflective surface 9 for a specific heating time. In other words, if the heating process is performed by using the device shown in FIG. 6 and setting the moving speed of the strip heater 8 in the long axis direction slower toward the center, the heating time will be constant in the short axis direction of the ellipse. Therefore, in the direction of long sleeves, the closer to the center the longer the heating time. the result,
The rate of increase in the film thickness period d of the multilayer film is also constant in the short axis direction, and becomes larger closer to the center in the long axis direction.

In this embodiment, the current flowing through the heater 8 is set so that the surface of the heated reflective surface 9 becomes 900 t: in order to produce a change in the film thickness period d of about 6 zero, and the current applied to the entire reflective surface 9 is heated. The treatment took about 5 hours. The entire apparatus was placed in a vacuum to prevent the W/C multilayer film and the strip heater 8 from being oxidized during the heat treatment.

Using the above-mentioned apparatus, the multilayer reflector is heat-treated by optimizing the moving speed of the heater 8 in order to produce a change in the film thickness period that satisfies Bragg's diffraction conditions at each location on the reflecting surface 9. After that, as shown in Figure 7, an excimer laser (wavelength 249 nm) 10 and a graphite target 1 are used.
A laser plasma X-ray source using a laser plasma Light collection efficiency was measured. When the light collection efficiency was compared between those subjected to the heat treatment according to the present invention and those not subjected to the heat treatment, the light collection efficiency was improved by about seven times in the case of those subjected to the heat treatment.

Example: 2 A W/C multilayer film was formed on a glass base material having a spheroidal reflective surface similar to that in Example 1 by RF magnetron sputtering.

Using a device as shown in Fig. 8, this multilayer film reflecting mirror is
Laser light from a YAG laser 14 (wavelength: 1.06 .mu.n+) was focused into a spot by a lens 15 and irradiated onto the reflective surface to perform local heat treatment. The multilayer film reflecting mirror 13 is mounted on an X-Y stage 16, and by moving the X-Y stage 16 relative to the laser beam, the entire reflecting surface can be scanned with the laser beam. There is.

With such an apparatus, by changing the scanning speed while keeping the laser output constant, heat treatment can be performed for different heat times at different locations.

Specifically, as shown in Figure 9 (a), a line is scanned at a constant scanning speed in a direction parallel to the short axis of the ellipse, and then the scanning speed is changed and the next line is scanned, which is repeated and reflected. The entire surface was heat treated. The heating time at this time is constant in the short axis direction (Fig. 9(C)), and is constant in the long axis direction (Fig. 9(b)
)), the scanning speed was slowed down and the heating time was increased closer to the center. As a result, the rate of increase in the film thickness period d of the multilayer film was also constant in the short axis direction, but in the long sleeve direction, it became much larger near the center, increasing by up to 6*.

The entire apparatus (excluding the YAG laser body) was placed in a vacuum to prevent the W/C multilayer film from being oxidized during the heat treatment.

When the light collection efficiency of the multilayer film reflector heat-treated in this way was evaluated using the apparatus shown in FIG. improved.

[Effects of the Invention] As described above, in the present invention, a multilayer film formed on a curved surface is heat-treated with different heating times for each location, and the film thickness period d is changed at each location so as not to satisfy the Bragg diffraction condition. By doing so, a high reflectance can be ensured over the entire reflecting surface of the curved multilayer film reflecting mirror. That is, the present invention has an extremely excellent effect in that it is possible to manufacture a multilayer film reflecting mirror with significantly higher efficiency and higher yield than conventional methods.

Further, by performing the heat treatment according to the present invention, the reflectance of the substance itself increases as the film thickness period increases, which also contributes to improving the efficiency of the multilayer mirror.

[Brief explanation of drawings]

FIG. 1 is a schematic cross-sectional view of a multilayer reflective mirror according to the present invention;
Figure 2 is an explanatory diagram explaining a reflecting mirror using an ellipsoid of revolution,
FIG. 3 is a graph showing the increase in the multilayer film period d with respect to the heat treatment temperature, FIG. 4 is an explanatory diagram illustrating the shape of the multilayer film reflector in the embodiment of the present invention, and FIG. 5 is a graph showing the increase in the multilayer film period d in the embodiment of the invention FIG. 6 is an explanatory diagram for explaining the formation method, FIG. 6 is an explanatory diagram for explaining the heat treatment method in the example of the present invention, FIG. 7 is a block diagram of the apparatus used to evaluate the light collection efficiency of the multilayer reflector, and FIG. FIG. 9 is a block diagram of a heat treatment apparatus according to another embodiment of the invention, and is an explanatory diagram illustrating a heat treatment method using the apparatus shown in FIG. 8. [Explanation of the symbols of the main parts...Base material 2...One substance forming the multilayer film 3...The other substance forming the multilayer film 4...Sputtering target 6...Rotation center axis 7... Central axis of oscillation 8... Strip heater 9... Reflecting surface 10... Excimer laser 1... Graphite target 2... X-ray detector 3... Multilayer film reflecting mirror 4 ...YAG laser 6...X-Y stage

Claims (1)

[Claims] After forming a multilayer film with a nearly uniform thickness period on a curved surface,
A method for manufacturing a multilayer film reflecting mirror, characterized in that the film thickness period of the multilayer film is changed from place to place so as to satisfy X-ray Bragg diffraction conditions by performing heat treatment at different heating times for each place.