| 摘要 |
A projection alignment method of aligning a mask and a wafer with each other through an optical imaging system and an apparatus for performing the method are disclosed. The apparatus comprises an optical illumination system for illuminating with highly coherent illumination light an alignment pattern formed with a stepped pattern on the wafer and a flat or planar portion of the wafer in the vicinity of the alignment pattern, an optical interference system for making reflected light from the alignment pattern on the wafer and reflected light from the flat portion of the wafer illuminated by the optical illumination system interfere with each other while optically superimposing optical images of both the reflected lights obtained through the optical imaging system on each other. A photo-electric conversion element subjects an interference pattern obtained by the optical interference system to photo-electric conversion, thereby obtaining a signal having a symmetry which represents a stepped portion of the alignment pattern, whereby alignment for the wafer is performed on the basis of the signal obtained from the photoelectric conversion element. With such a construction, any influence of uneven thickness of a resist film applied on the alignment pattern can be reduced and hence a highly symmetrical signal corresponding to the stepped portion of the alignment pattern can be obtained, thereby realizing alignment with high precision.
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