OPTICAL MATERIAL FOR PHOTOLITHOGRAPHY, MEASURING METHOD OF ITS TRANSMITTANCE, AND PHOTOLITHOGRAPHY DEVICE

摘要

PROBLEM TO BE SOLVED: To realize a projection aligner due to photolithography using light with a wavelength of 185 nm or less as a light source by using a calcium fluoride crystal with high transmittance as the optical material of a photolithography device. SOLUTION: Light being emitted from a light source 1 is uniformly applied to a mask 3 where a pattern is formed via a lighting optical system 2. Light from the pattern being formed in the mask 3 forms a mask pattern image on a wafer 9 via a projection optical system 8. In all refraction optical members (lens constituents) for composing the projection optical system 8, an optical material made of a calcium fluoride crystal is used. In the measurement of the inside transmittance of the optical material, a measuring sample with a thickness of 30 mm or more is cut from the optical material consisting of the calcium fluoride crystal, and the transmittance in a specific wavelength of 185 nm or less of the sample is actually measured. Influence due to the decline of the transmittance corresponding to a surface reflection loss is eliminated from the actually measured transmittance, thus calculating the inside transmittance per unit thickness.