Plasma and Fusion Research

Volume 21, 2406016 (2026)

Regular Articles

Measurement of Visible Emission from Laser-Produced Sn Plasma in Hydrogen Atmosphere
Shusen GAO1), Keishin WATANABE1), Yu TAKEHIRO1), Yuito NISHII1), Maki KISHIMOTO1), Tomoyuki JOHZAKI1,2), Atushi SUNAHARA2,3), Kotaro YAMASAKI1), Takeshi HIGASHIGUCHI4), Shinichi NAMBA1)
1)
Graduate School of Advanced Science and Engineering, Hiroshima University, 1-3-2 Kagamiyama, Higashihiroshima, Hiroshima 739-8527, Japan
2)
Institute of Laser Engineering, Osaka University, 2-6 Yamadaoka, Suita, Osaka 565-0871, Japan
3)
Center for Material under Extreme Environment, Purdue University, 610 Purdue Mall, West Lafayette, IN 47907, U.S
4)
Department of Electrical and Electronic Engineering, Utsunomiya University, 350 Minemachi Utsunomiya, Tochigi 321-8505, Japan
(Received 30 August 2025 / Accepted 20 November 2025 / Published 31 March 2026)

Abstract

Laser-produced tin (Sn) plasma is extensively used as an extreme ultraviolet (EUV) light source for advanced lithography; however, the collector mirror lifetime is considerably shortened by high-energy debris from the plasma. The introduction of hydrogen (H2) gas into the plasma region can mitigate debris through ion–neutral collisions and chemical reactions forming gaseous stannane (SnH4). However, the detailed Sn-H interaction mechanisms remain uninvestigated. Herein, visible emission spectroscopy was used to investigate the spatiotemporal behaviors of Sn and H plasmas generated by 12-ps, 1,064-nm laser pulses incident on a solid Sn target in a 100 Pa H2 atmosphere. Spatiotemporal-resolved measurements of Hα and Hβ lines revealed prompt hydrogen excitation following plasma generation, with electron temperatures of 1–2 eV and electron densities up to 1 × 1017 cm−3 near the target. These conditions aid the formation of hydrogen radicals that react with Sn atoms/ions to produce SnH4, contributing to the effective mitigation of debris. These findings offer insights into the optimization of the EUV source performance and the prolongation of the optical component lifetime.

Keywords

laser-produced plasma, tin plasma, hydrogen gas, EUV lithography, debris removal, plasma spectroscopy, electron temperature, electron density

DOI: 10.1585/pfr.21.2406016

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