Patent Number: 051827638
Section: summary

FIELD OF THE INVENTION AND RELATED ART This invention relates generally to a reflection device with a mirror having a multilayered film. In another aspect, the invention relates to a scanning system or an exposure apparatus with such a reflection device. More particularly, the invention is concerned with a reflection device with a mirror having a multilayered film, effective to reflect light of a wavelength 200 nm or less, such as X-rays, vacuum ultraviolet rays or the like, to produce expanded or diffused reflection light. In another aspect, the invention is concerned with a scanning system or an exposure apparatus with such a reflection device. Conventionally, for reflection of light of a wavelength 200 nm or less, having a small divergent angle, such as X-rays or vacuum ultraviolet rays, for example, and for enlarging the diameter of the light, a fixed convex mirror or a swingingly moved convex or flat mirror is used. If, when such a mirror is used, it is desired to provide an increased reflectivity with respect to a particular wavelength, as compared with the other wavelengths, it may be considered that a multilayered film designed with respect to the particular wavelength may be formed on the mirror surface. However, the provision of such a multilayered film on the mirror surface involves such problems as follows. In a fixed convex mirror, different portions of light inputted to the reflection surface of the mirror impinge on different positions on the convex reflection surface of the mirror. As a result, at these positions, the inputted light rays have different angles (angles of incidence) with respect to the reflection surface. On the other hand, generally a multilayered film is so optimized that it exhibits its performance when light of a predetermined wavelength is inputted thereto with a predetermined angle (angle of incidence). Accordingly, in the case of the fixed convex mirror, there is a possibility that, with regard to the predetermined wavelength, only the reflection light rays produced around the peak of the mirror, for example, have intensified strength (as compared with the other wavelengths), and those reflection light rays produced by the other portions of the mirror have intensified strength with respect to some wavelength other than the predetermined wavelength. If this occurs, then the reflection light produced by this mirror has spatial non-uniformness in wavelength, in its section. In a swingable mirror, on the other hand, the inclination of the reflection surface to the light inputted thereto changes with time. As a result, the angle of incidence of the light with respect to the reflection surface also changes with time. This leads to a situation that, in the produced reflection light with which a surface to be illuminated is scanned, such a light component as having a relatively strong light intensity has a varying wavelength. When such a fixed mirror or a swingable mirror is used in an illumination system of an X-ray exposure apparatus, for example, to expose a semiconductor wafer with X-rays reflected by this mirror, since generally the sensitivity of a resist applied to the wafer has a dependence upon the wavelength, the non-uniformness in wavelength or the variation in wavelength such as described above presents uniform exposure. SUMMARY OF THE INVENTION It is accordingly a primary object of the present invention to provide an improved reflection mirror which is free from the above-described inconveniences. It is another object of the present invention to provide a reflection device with such a reflection mirror. It is a further object of the present invention to provide a scanning system with such a reflection device. It is yet another object of the present invention to provide an exposure apparatus with such a reflection device. In accordance with an aspect of the present invention, there is provided a fixed or swingable reflection mirror for reflecting a received radiation beam to produce a reflection beam, wherein the radiation beam is inputted to said reflection mirror with an angle of incidence which changes with position on said reflection mirror, characterized in that: said reflection mirror has a multilayered film effective to provide an increased relative reflectivity with respect to a predetermined wavelength of the reflection beam, wherein a layer of said multilayered film has a thickness which changes with position so as to substantially avoid a shift of said wavelength of the reflection beam dependent upon the angle of incidence. In accordance with another aspect of the present invention, there is provided a reflection device including a movable mirror for reflecting a received radiation beam to produce a reflection beam, wherein said movable mirror is so moved that, with respect to a plane of incidence of the radiation beam, a position and an angle of incidence of the radiation beam are shifted with the movement of said movable mirror, characterized in that: said movable mirror has a multilayered film effective to provide an increased relative reflectivity of a predetermined wavelength of the reflection beam, wherein each layer of said multilayered film has a thickness which changes with position so as to substantially avoid a shift of said wavelength with the shift in the angle of incidence of the radiation beam. In accordance with a further aspect of the present invention, there is provided a scanning system, comprising: a radiation source; a reflection mirror for reflecting a radiation beam from said radiation source to produce a reflection beam, said reflection mirror having a multilayered film effective to provide an increased relative reflectivity with respect to a predetermined wavelength of the reflection beam, wherein a layer of said multilayered film has a thickness which gradually increases with an increase in a distance from said radiation source in a plane of incidence of the radiation beam; and a driving device for swinging said reflection mirror so as to shift a position and an angle of incidence of the radiation beam upon said reflection mirror, in the plane of incidence of the radiation beam, to thereby scanningly deflect the reflection beam. In accordance with yet another aspect of the present invention, there is provided an exposure apparatus having a reflection mirror for reflecting a received radiation beam to produce a reflection beam, to expose a substrate with the reflection beam, wherein the radiation beam is inputted to said reflection mirror with an angle of incidence which changes with position on said reflection mirror, characterized in that: said reflection mirror has a multilayered film effective to provide an increased relative reflectivity with respect to a predetermined wavelength of the reflection beam, wherein each layer of said multilayered film has a thickness which changes with position so as to substantially avoid a shift of said wavelength of the reflection beam dependent upon the angle of incidence. In this type of exposure apparatus, said reflection mirror may be fixed or swingingly moved. In accordance with a still further aspect of the present invention, there is provided an X-ray exposure apparatus, comprising: an X-ray source; and an illumination system for illuminating a mask pattern with X-rays from said X-ray source to expose a wafer to the mask pattern; wherein said illumination system includes a reflection mirror for reflecting the X-rays from said X-ray source to produce a reflection beam and a driving device for swinging said reflection mirror; wherein said reflection mirror has a multilayered film effective to provide an increased relative reflectivity with respect to a predetermined wavelength of the reflection beam; wherein each layer of said multilayered film of said reflection mirror has a thickness which gradually increases with an increase in a distance from said X-ray source in a plane of incidence of the X-rays; and wherein said driving device swings said reflection mirror so as to shift a position and an angle of incidence of the X-rays upon said reflection mirror in the plane of incidence, to thereby scanningly deflect the reflection beam to scan the mask pattern with the deflected reflection beam. In the present invention, as the reflection mirror, one having a flat reflection surface, one having a concave reflection surface or one having a convex reflection surface may by used. In one preferred form of the present invention, the mirror has a flat reflection surface and the driving device rotationally moves the reflection mirror through a rotational shaft space from the reflection surface. In another preferred form, the reflection mirror has a convex reflection surface and the driving device rotationally moves the reflection mirror through a rotational shaft spaced from the reflection surface or, alternatively, the driving device oscillatingly moves the reflection mirror in a direction traversing the radiation beam. Preferably, in the present invention, the reflection mirror is disposed so that the radiation beam such as X-rays is grazingly inputted (at a certain grazing angle) to the reflection surface thereof, so as to ensure enhanced reflectivity. It is to be noted here that the term "plane of incidence" means a plane that contains the radiation beam inputted to the reflection surface of the reflection mirror and the reflection beam produced by this reflection surface. These and other objects, features and advantages of the present invention will become more apparent upon a consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings.