IMAGING OPTICAL SYSTEM AND PROJECTION ALIGNER

摘要

A high-performance imaging optical system capable of positively minimizing double refraction occurring when going to a shorter wavelength and providing a good contrast, and a high-performance projection aligner. The imaging optical system is characterized by being provided with at least one refraction member consisting of an SrF2 crystal material. This crystal material, when used, can positively make smaller the effects of double refraction than when other crystal materials are used when a used wavelength is near 157 nm (150 nm-160 nm).