Time-resolved two-dimensional profiles of electron density and temperature of laser-produced tin plasmas for extreme-ultraviolet lithography light sources

Kentaro Tomita, Yuta Sato, Syouichi Tsukiyama, Toshiaki Eguchi, Kiichiro Uchino, Kouichiro Kouge, Hiroaki Tomuro, Tatsuya Yanagida, Yasunori Wada, Masahito Kunishima, Georg Soumagne, Takeshi Kodama, Hakaru Mizoguchi, Atsushi Sunahara, Katsunobu Nishihara

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Abstract

Time-resolved two-dimensional (2D) profiles of electron density (n e) and electron temperature (T e) of extreme ultraviolet (EUV) lithography light source plasmas were obtained from the ion components of collective Thomson scattering (CTS) spectra. The highest EUV conversion efficiency (CE) of 4% from double pulse lasers irradiating a Sn droplet was obtained by changing their delay time. The 2D-CTS results clarified that for the highest CE condition, a hollow-like density profile was formed, i.e., the high density region existed not on the central axis but in a part with a certain radius. The 2D profile of the in-band EUV emissivity (ηEUV) was theoretically calculated using the CTS results and atomic model (Hullac code), which reproduced a directly measured EUV image reasonably well. The CTS results strongly indicated the necessity of optimizing 2D plasma profiles to improve the CE in the future.

Original languageEnglish
Article number12328
JournalScientific reports
Volume7
Issue number1
DOIs
Publication statusPublished - Dec 1 2017

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All Science Journal Classification (ASJC) codes

  • General

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