| 摘要 |
PROBLEM TO BE SOLVED: To obtain a large diameter fluoride crystal for optical lithography, which transmits ultra-violet rays of <250 nm and has a small birefringence, by annealing an optical fluoride crystal. SOLUTION: The fluoride crystal for optical lithography is obtained by arranging the optical fluoride crystal 16 in a chamber 12 of an annealing furnace 20 having heating elements 22, 24, then heating the crystal 16 to an annealing temperature along with the shortest heat transfer pathway, and after keeping the crystal 16 at the annealing temperature, gradually cooling the crystal 16. COPYRIGHT: (C)2004,JPO |
