Patent Number: 053944518
Section: summary

FIELD OF THE INVENTIONS AND RELATED ART This invention relates to an optical arrangement suitably usable, for example, in an exposure apparatus such as an X-ray exposure apparatus which uses, as a light source, synchrotron radiation light produced by a charged particle accumulation ring (synchrotron ring). An example of an exposure apparatus, which uses synchrotron radiation light as a light source to transfer a fine mask pattern such as VLSI to a wafer, is illustrated in FIGS. 8A and 8B wherein synchrotron radiation light emitted from an emission point 12 of a synchrotron ring (SOR ring) 11 is reflected by a mirror 15, swinging in the direction of the arrow, and thus it is expanded in a direction (Y direction) perpendicular to the orbit plane of the synchrotron ring 11. The expanded light illuminates a mask (original) 13 whereby a pattern of the mask is transferred to a wafer 14. In the illustrated example, the distance from the emission point 12 to the mirror 15 is, e.g., 5 m; the distance from the mirror 15 to the mask 13 is, e.g., about 5 m; the distance from the mask 13 to the wafer 14 (i.e. "proximity gap") is, e.g., about 30 microns; and the size of the transfer region is about 20 mm square. In this example, the acceptance angle (the angle of divergence of light, from a point light source, that can be accepted by an illumination system (mirror 15) for projection of light to a mask and a wafer) with respect to a direction (X direction) parallel to the orbit plane of the synchrotron ring is 2 mrad, and the tilt in the X direction of the synchrotron radiation light impinging on the mask 13 is 1 mrad (max.) while the tilt thereof in the Y direction is 2 mrad (max.). As a result, there occurs distortion (called "run-out error") in the mask pattern transferred to the wafer 14. The magnitude of this distortion in the Y direction is 0.06 micron (max.). FIGS. 9A and 9B show another example of a radiation exposure apparatus by which the problem of run-out error such as described above may be solved. In the apparatus of FIGS. 9A and 9B, for transferring a mask pattern of a mask 33 to a wafer 34, a beam emitted from an emission point 32 of a synchrotron ring 31 is reflected by a rotational hyperboloid reflecting mirror 35 and then by a rotational paraboloid reflecting mirror 36, whereby it is collimated with respect to the X and Y directions. In this structure, however, the system comprising the reflecting mirrors 35 and 36 has the same focal distance in the X and Y directions and, therefore, the angle of acceptance of the synchrotron radiation is the same with respect to both the X and Y directions. However, since the synchrotron radiation light has a larger divergence angle in the X direction than that in the Y direction, with this system, it is only possible to retrieve or accept a very small portion of the light in the X direction. Namely, most of the light emitted from the synchrotron is not used and, naturally, the efficiency of using synchrotron radiation light is low. This consequently requires a prolonged exposure time. SUMMARY OF THE INVENTION It is accordingly an object of the present invention to provide an optical arrangement by which synchrotron radiation light can be collimated in the X and Y directions and, additionally, by which the angle of acceptance of the synchrotron radiation light with respect to the X and Y directions can be enlarged. It is another object of the present invention to provide an improved semiconductor device manufacturing method which uses the optical arrangement described above. 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.