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Proceedings Paper

Novel low thermal expansion material for EUV application
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Paper Abstract

In extreme ultraviolet (EUV) lithography technology, ultra low thermal expansion material is required as photomask substrate. We have previously developed Ti-doped silica glass which exhibits both ultra low coefficient of thermal expansion (CTE) and high homogeneity for EUV substrate. On the other hand, we have been investigating other candidate materials which have low CTE, from the viewpoint of structural chemistry. Silica glass is well-known as a low thermal expansion material and the reason is explained that in the open structure of silica glass two factors, expansion and shrinkage, compete with each other with increase in temperature. The network of silica glass consists of tetrahedra like quartz crystal. In this structure, Si is stably present with a valence of 4 and a coordination number of 4. We have carried out an atomistic simulation and estimated the volume change of oxide materials which may have the same structural transformation mechanism as SiO2. As a result, the volume of SnO2 with quartz structure (quartz-SnO2), in which Sn was present with a valance of 4 and a coordination number of 4, decreased with increase in temperature, that is, the density of quartz-SnO2 increased. Thus, it was indicated that the glass with lower CTE than that of silica glass could be obtained with substituting Sn for Si. Based on this hypothesis, we have prepared Sn-doped silica glass by Asahi silica glass producing method. The synthesized Sn-doped silica glass exhibited lower CTE than that of an ordinary silica glass.

Paper Details

Date Published: 23 March 2006
PDF: 7 pages
Proc. SPIE 6151, Emerging Lithographic Technologies X, 61511A (23 March 2006); doi: 10.1117/12.655931
Show Author Affiliations
Mitsuhiro Kawata, Asahi Glass Co., Ltd. (Japan)
Akira Takada, Asahi Glass Co., Ltd. (Japan)
Hideaki Hayashi, Asahi Glass Co., Ltd. (Japan)
Naoki Sugimoto, Asahi Glass Co., Ltd. (Japan)
Shinya Kikugawa, Asahi Glass Co., Ltd. (Japan)

Published in SPIE Proceedings Vol. 6151:
Emerging Lithographic Technologies X
Michael J. Lercel, Editor(s)

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