In-situ measurements of VUV optical materials for F2 laser

Akira Sumitani; Yasuo Itakura; Fumika Yoshida; Youichi Kawasa; Jing Zhang; Noriyoshi Kanda; Toshiro Itani

doi:10.1117/12.474557

30 July 2002 In-situ measurements of VUV optical materials for F2 laser

Akira Sumitani, Yasuo Itakura, Fumika Yoshida, Youichi Kawasa, Jing Zhang, Noriyoshi Kanda, Toshiro Itani

Proceedings Volume 4691, Optical Microlithography XV; (2002) https://doi.org/10.1117/12.474557
Event: SPIE's 27th Annual International Symposium on Microlithography, 2002, Santa Clara, California, United States

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.

Citation Download Citation

Akira Sumitani, Yasuo Itakura, Fumika Yoshida, Youichi Kawasa, Jing Zhang, Noriyoshi Kanda, and Toshiro Itani "In-situ measurements of VUV optical materials for F2 laser", Proc. SPIE 4691, Optical Microlithography XV, (30 July 2002); https://doi.org/10.1117/12.474557

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KEYWORDS

Transmittance

Vacuum ultraviolet

Laser irradiation

Laser development

Spectrophotometry

Lithography

Silicon

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