20 May 2004 Properties of EUV emissions from laser-produced tin plasmas
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Extreme ultraviolet (EUV) emission from laser produced plasma attracts much attention as a next generation lithography source. The characterization of EUV emission has been carried out using GEKKO XII laser system. The twelve beams irradiated tin or tin-oxide coated spherical targets uniformly and dependence of EUV spectra on laser intensity were obtained with a transmission grating spectrometer and two grazing incidence spectrometers. The EUV Conversion Efficiency (CE, the ratio of EUV energy at the wavelength of 13.5 nm with 2 % bandwidth to incident laser energy) was measured using an absolutely calibrated EUV calorimeter. Optimum laser intensities for the highest conversion were found to be 0.5- 1x1011 W/cm2 with CE of 3 %. The spectroscopic data indicate that shorter wavelength emission increases at higher laser intensities due to excessive heating beyond optimum temperatures (20- 40 eV). The CE was almost independent on the initial coating thickness down to 25 nm.
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Yoshinori Shimada, Hiroaki Nishimura, Kazuhisa Hashimoto, Michiteru Yamaura, Keisuke Shigemori, Mitsuo Nakai, Shinsuke Fujioka, Shigeaki Uchida, Tomoharu Okuno, Takahiro Hibino, Nobuyoshi Ueda, Ryoji Matsui, Yezheng Tao, Keiji Nagai, Takayoshi Norimatsu, Toru Kawamura, Atsushi Sunahara, Katsunobu Nishihara, Noriaki Miyanaga, Masahiro Nakatsuka, Yasukazu Izawa, Chihiro Yamanaka, "Properties of EUV emissions from laser-produced tin plasmas", Proc. SPIE 5374, Emerging Lithographic Technologies VIII, (20 May 2004); doi: 10.1117/12.534959; https://doi.org/10.1117/12.534959

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