METHOD FOR PRODUCING CRYSTAL AND OPTICAL SYSTEM INCLUDING OPTICAL ELEMENT PRODUCED BY THE SAME, AND EXPOSURE EQUIPMENT

摘要

PROBLEM TO BE SOLVED: To provide a method for producing a fluorite crystal in which the fluorite crystal having high durability and high transmittance required for vacuum ultraviolet photolithographic equipment or the like can be stably produced. SOLUTION: The reduction of rare-earth element impurities is indispensable to improve optical properties. The degree of the reduction by the effect of recrystallization is indirectly grasped by comparing the trend of the content of at least one element selected from Mg, Sr, and Ba in a process. Management of production steps by the above method allows a high quality fluorite crystal having reduced amount of rare-earth element impurities to be stably produced without a highly developed analysis of rare-earth elements. COPYRIGHT: (C)2003,JPO