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Proceedings Paper

Properties of large CaF2 crystals grown by CZ method for lens materials
Author(s): Hiroyuki Yanagi; T. Nawata; Yoji Inui; Y. Hatanaka; E. Nishijima; Tsuguo Fukuda
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Paper Abstract

CaF2 (Calcium fluoride) lens materials are required for the composition of F2 laser lithography stepper. Recently, it is reported that both <111> crystal and <100> crystal are necessary for the lens blanks, which can resolve the intrinsic birefringence of CaF2. Although CaF2 single crystal has been produced by Bridgman method, some problems are pointed out on the optical properties and production yield especially on <100> crystal with large diameter. So it is worried that the amount of the supply of CaF2 will be short when F2 stepper will start on a large scale. To resolve the above mentioned problems, we tried to grow a large CaF2 single crystal by Czochralski (CZ) technique, because we expected that CZ technique could provide higher productivity and higher quality which mean lower residual stress than conventional method. CZ technique can also easily control the growing crystal axis by the selection of seed crystal. Consequently we succeeded in growth both <111> and <100> direction single crystal which has 210mm diameter and 150mm length. The obtained crystal is a single crystal over a whole boule and it shows high transparency in vacuum ultraviolet region. Moreover it shows very low birefringence value and good homogeneity after annealing process. We hope our challenge should prompt the development of F2 lithography.

Paper Details

Date Published: 28 May 2004
PDF: 8 pages
Proc. SPIE 5377, Optical Microlithography XVII, (28 May 2004); doi: 10.1117/12.556614
Show Author Affiliations
Hiroyuki Yanagi, Tokuyama Corp. (Japan)
T. Nawata, Tokuyama Corp. (Japan)
Yoji Inui, Tokuyama Corp. (Japan)
Y. Hatanaka, Tokuyama Corp. (Japan)
E. Nishijima, Tokuyama Corp. (Japan)
Tsuguo Fukuda, Tohoku Univ. (Japan)


Published in SPIE Proceedings Vol. 5377:
Optical Microlithography XVII
Bruce W. Smith, Editor(s)

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