Tomita Kentaro, Sato Yuta, Tsukiyama Syouichi, Eguchi Toshiaki, Uchino Kiichiro, Kouge Kouichiro, Tomuro Hiroaki, Yanagida Tatsuya, Wada Yasunori, Kunishima Masahito, Soumagne Georg, Kodama Takeshi, Mizoguchi Hakaru, Sunahara Atsushi, Nishihara Katsunobu
Interdisciplinary Graduate School of Engineering Sciences, Kyushu University, 6-1 Kasugakoen, Kasuga, 816-8580, Fukuoka, Japan.
Gigaphoton Inc., 400 Yokokurashinden, Oyama, 323-8558, Tochigi, Japan.
Sci Rep. 2017 Oct 2;7(1):12328. doi: 10.1038/s41598-017-11685-0.
Time-resolved two-dimensional (2D) profiles of electron density (n ) and electron temperature (T ) 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 (η) 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.
通过集体汤姆逊散射（CTS）光谱的离子成分，获得了极紫外（EUV）光刻光源等离子体的电子密度（n）和电子温度（T）的时间分辨二维（2D）分布。通过改变双脉冲激光照射锡液滴的延迟时间，获得了4%的最高EUV转换效率（CE）。二维CTS结果表明，在最高CE条件下，形成了类似空心的密度分布，即高密度区域不在中心轴上，而是存在于具有一定半径的部分。利用CTS结果和原子模型（Hullac代码）从理论上计算了带内EUV发射率（η）的二维分布，该分布较好地再现了直接测量的EUV图像。CTS结果有力地表明，未来优化二维等离子体分布对于提高CE的必要性。
