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7 March 2008 Fluoride single crystals for the next generation lithography
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BaLiF3 single crystal has been studied as the candidate for the last lens material of the next generation high index immersion lithography system. Although the refractive index of BaLiF3 is 1.64 at 193nm which is not sufficient for the requirement, other optical properties such as 193nm transparency and laser durability fulfill the requirement. It is estimated that the cause of both high SBR part and inhomogeneity of refractive index of BaLiF3 seems to present along the faces of slip planes which are observed by crossed Nicol observation. As a result of comparative study of various direction perpendiculars to the growth axis, good crystallinity with less slip planes has been obtained by shifting the growth axis from <100> which is adequate for the last lens production. MgF2 single crystal studied as the polarizer material for high power ArF laser oscillator, and crystal with excellent laser durability and large diameter (>100mm) has been developed by CZ technique. In addition crystals oriented along both c-axis and a-axis were successfully grown.
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Teruhiko Nawata, Yoji Inui, Toshiro Mabuchi, Naoto Mochizuki, Isao Masada, Eiichi Nishijima, Hiroki Sato, and Tsuguo Fukuda "Fluoride single crystals for the next generation lithography", Proc. SPIE 6924, Optical Microlithography XXI, 69242L (7 March 2008);

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