| 摘要 |
PROBLEM TO BE SOLVED: To obtain the concept of a substitute objective lens using material composition of low wavelength and obtaining new applicability, especially, in microlithography by using two kinds of crystal for the objective lens. SOLUTION: The objective lens equipped with a lens consisting of at least two kinds of crystal is used. It is desirable that the lens is constituted of at least two kinds of fluoride, especially, CaF2, BaF2, SrF2, LiF, NaF or KF. The lens has pure refractivity and includes a lens constituted of BaF2, SrF2, NaF, LiF or KF. Then, it is the projection objective lens for microlithography corrected to illuminate by using an F2 excimer laser in the wavelength of 157 nm. Thus, material pair for decolorizing of 157 nm optical system is obtained for the first time by combining two kinds of crystal fluoride, especially, CaF2, BaF2, SrF2, LiF, NaF or KF or combining mixed crystal fluoride.
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