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Proceedings Paper

In-situ measurements of VUV optical materials for F2 laser
Author(s): Akira Sumitani; Yasuo Itakura; Fumika Yoshida; Youichi Kawasa; Jing Zhang; Noriyoshi Kanda; Toshiro Itani
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Paper Abstract

F2 laser lithography (wavelength:157 nm) is a candidate of post-ArF excimer laser lithography. In order to test the characteristics of vacuum ultraviolet (VUV) materials for F2 laser lithography, we developed an evaluation system consisting of a 1 kHz F2 laser, an in-situ real-time transmittance measurement unit and an in-situ VUV spectrophotometer. The precision of the real-time transmittance measurement is +/- 0.5%. The precision of the VUV spectrophotometer measurement is +/- 0.5% for scanned wavelengths (140 - 300 nm) and +/- 0.1% for a constant wavelength (at 157.6 nm). Due to F2 laser irradiation cleaning, the transmittance of uncoated calcium fluoride (CaF2) substrates and of F2 laser coatings at first rapidly and then gradually increased. Thereafter the transmittance remained constant. Results of the real-time transmittance and the VUV spectrophotometer measurement were almost identical. In addition, durability tests of CaF2 substrates and of F2 laser coatings were performed with a 4 kHz F2 laser for more than 10 billion pulses (Bpls). After the initial transmittance increase of CaF2 substrates, no change in transmittance was observed during more than 10 Bpls. In order to maintain the CaF2 substrate transmittance, silicon compounds have to be removed from the purge gas and from the irradiation chamber where optical materials are placed. F2 laser coating quality varied enormously between suppliers.

Paper Details

Date Published: 30 July 2002
PDF: 10 pages
Proc. SPIE 4691, Optical Microlithography XV, (30 July 2002); doi: 10.1117/12.474557
Show Author Affiliations
Akira Sumitani, Komatsu Ltd. (Japan)
Yasuo Itakura, Komatsu Ltd. (Japan)
Fumika Yoshida, Komatsu Ltd. (Japan)
Youichi Kawasa, Komatsu Ltd. (Japan)
Jing Zhang, Komatsu Ltd. (Japan)
Noriyoshi Kanda, Semiconductor Leading Edge Technologies, Inc. (Japan)
Toshiro Itani, Semiconductor Leading Edge Technologies, Inc. (Japan)

Published in SPIE Proceedings Vol. 4691:
Optical Microlithography XV
Anthony Yen, Editor(s)

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