Patent Number: 051503913
Section: summary

FIELD OF THE INVENTION AND RELATED ART This invention relates to an exposure apparatus and, more particularly, to an exposure apparatus for transferring and printing an image of an original, such as a mask, onto a workpiece such as a semiconductor wafer, with high precision. With recent increasing degree of integration of semiconductor integrated circuit, in an exposure apparatus (aligner) for manufacture of the same, further enhancement of transfer precision is required. As an example, for an integrated circuit of 256 megabit DRAM, an exposure apparatus capable of printing a pattern of a linewidth of 0.25 micron order is necessary. As such super-fine pattern printing exposure apparatus, a proximity exposure apparatus which uses orbit radiation light (SOR X-rays) has been proposed. The orbit radiation light has a sheet beam shape, uniform in a horizontal direction. Thus, for exposure of a plane of certain area, many proposals have been made, such as follows: (1) Scan exposure method wherein a mask and a wafer are moved in a vertical direction whereby the surface is scanned with X-rays of sheet beam shape in a horizontal direction; (2) Scan mirror exposure method wherein X-rays of sheet beam shape are reflected by an oscillating mirror whereby a mask and a wafer are scanned in a vertical direction; and (3) Simultaneous exposure method wherein X-rays of sheet beam shape in a horizontal direction are diverged in a vertical direction by an X-ray mirror having a reflection surface machined into a convex shape, whereby an exposure region as a whole is irradiated simultaneously. The inventors of the subject application have cooperated to devise such a simultaneous exposure type X-ray exposure apparatus, which is disclosed in Japanese Laid-Open Patent Application No. 243519/1989. An X-ray exposure apparatus involves the following problems. Ultraviolet rays can be blocked substantially completely by a ultraviolet-ray reflective thin film such as a chromium film. For this reason, in conventional exposure apparatuses that use ultraviolet rays or the like as an exposure light, only by covering a region on the mask surface outside the exposure region with a patterning material such as chromium in a similar manner as the blocking portion of a pattern formed in the exposure region, it is possible to prevent exposure of a non-desired region on a wafer. In an X-ray exposure apparatus, however, an absorptive material such as gold, chromium or the like used as an X-ray blocking portion of a mask pattern in the exposure region can not have a sufficient thickness in the case of a linewidth of 0.25 micron, and for this reason a small amount of X-rays are transmitted therethrough. In practical examples, the transmission factor of this portion reaches several percentages. As a result, only by covering a region on the mask surface outside the exposure region with a patterning material such as gold, chromium or the like in the same manner as the X-ray blocking portion of the mask pattern in the exposure region, the protection is insufficient and such portion of the wafer, not desired to be exposed, is exposed with the X-rays. For example, it is now assumed that, by using a mask such as shown in FIG. 1B, different portions (show areas) S0-S8 of a wafer such as shown in FIG. 1A are going to be exposed. The mask shown in FIG. 1B has an exposure region MC in which a circuit pattern (not shown) is formed. Denoted at MM is a pattern, outside the exposure region, covering this portion with an absorptive material such as gold, chromium or the like having a similar thickness as of an X-ray blocking portion of the circuit pattern MC region. Inside a broken line MA corresponds to a region to be irradiated with X-rays. In this example, in the wafer shown in FIG. 1A, the shot area S0 is exposed to X-rays passing through the non-exposure region pattern MM of the mask shown in FIG. 1B, during exposures of the surrounding shot areas S1-S8. Inside area of each circle shown in FIG. 1A corresponds to the region to be exposed to the X-rays passed through the non-exposure region pattern MM, during exposure of each shot area. As an example, the central hatched portion of the shot area S0 in FIG. 1A is subjected to four undesirable exposures during the exposures of the surrounding shot areas S2, S4, S5 and S7. If the quantity of irradiation (exposure) in the exposure region becomes non-uniform such as above, the transfer precision is deteriorated. A solution for such a problem may be enlargement of the film thickness at the non-exposure region pattern MM of gold, chromium or the like, to be patterned on a mask. However, possible non-uniformness in thickness causes a stress which, in turn, produces distortion. As a result, the precision in size of the pattern in the exposure region is deteriorated. On the other hand, an exposure apparatus has been proposed wherein four sides are enclosed by blocking members, separate from a mask pattern, to define an aperture through which the exposure light is projected, whereby only the exposure region on a mask is irradiated. Each blocking member defining this aperture can have a sufficient thickness and, therefore, if such an aperture is applied to an X-ray exposure apparatus, it is possible to reduce the X-ray irradiation to the non-exposure region to a small degree that can be neglected. Also, an exposure apparatus with such an aperture is known wherein a light blocking member and an alignment optical system for detecting the relative position of a mask and a wafer are mounted on a dual-axis stage, by which they can be moved in a plane parallel to the mask or wafer surface and in X and Y directions. This structure makes it possible to set the blocking member and the alignment optical system at a desired position and, therefore, it can meet various sizes of a shot area (or semiconductor chip). Further, by commonly using a stage for the movement of the blocking member and for the movement of the alignment optical system, the structure of the device can be simplified and reduced in weight. SUMMARY OF THE INVENTION The present invention in an aspect pertains to an exposure apparatus with a rectangular aperture defined by enclosing four sides with light blocking members, and it is a primary object of the present invention to provide an exposure apparatus wherein there is no necessity of using a stage exclusive for the aperture and wherein each light blocking member is immovable in a lateral direction (parallel to a corresponding side of the aperture), such that the size of each light blocking member can be made small. 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.