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Applied Optics

Applied Optics


  • Editor: James C. Wyant
  • Vol. 45, Iss. 7 — Mar. 1, 2006
  • pp: 1380–1385

Postfluorination of fluoride films for vacuum-ultraviolet lithography to improve their optical properties

Yusuke Taki, Shunji Watanabe, and Akira Tanaka  »View Author Affiliations

Applied Optics, Vol. 45, Issue 7, pp. 1380-1385 (2006)

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Transmittance of fluoride films prepared by various kinds of deposition methods is not sufficient for a vacuum-ultraviolet (VUV) stepper application. Moreover, moisture penetrates into fluoride films because of porous structures. Then the moisture reacts with the fluoride chemically, and the photoabsorption of the films increases with elapsed time. Postfluorination treatment, in which F-poor areas of fluoride films are sufficiently fluorinated and the film structures are modified to be denser, has been developed. The postfluorination treatment was performed at 0.1 MPa of diluted F 2 gas in a special apparatus made of nickel. This treatment reduces photoabsorption of fluoride films and prevents photoabsorption from increasing again with elapsed time. In a long-time F 2 laser irradiation test, the transmittance of as-deposited fluoride films remarkably degraded with irradiation. On the other hand, there is no tendency of transmittance degradation in the case of postfluorinated fluoride films. The postfluorination is able to improve the optical performance of fluoride films, promising the highest coating level for VUV lithography.

© 2006 Optical Society of America

OCIS Codes
(310.3840) Thin films : Materials and process characterization
(310.6860) Thin films : Thin films, optical properties

ToC Category:
Short and Intense Wavelength Coatings

Original Manuscript: March 1, 2005
Manuscript Accepted: June 28, 2005

Yusuke Taki, Shunji Watanabe, and Akira Tanaka, "Postfluorination of fluoride films for vacuum-ultraviolet lithography to improve their optical properties," Appl. Opt. 45, 1380-1385 (2006)

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  1. S. Niisaka, T. Saito, J. Saito, A. Tanaka, A. Matsumoto, M. Otani, R. Biro, C. Ouchi, M. Hasegawa, Y. Suzuki, and K. Sone, 'Development of optical coatings for 157-nm lithography. I. Coating materials,' Appl. Opt. 41, 3242-3247 (2002). [CrossRef] [PubMed]
  2. Y. Taki, 'Film structure and optical constants of magnetron-sputtered fluoride films for deep ultraviolet lithography,' Vacuum 74, 431-435 (2004). [CrossRef]
  3. Y. Taki and K. Muramatsu, 'Hetero-epitaxial growth and optical properties of LaF3 on CaF2,' Thin Solid Films 420-421, 30-37 (2002). [CrossRef]

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