Short-wavelength out-of-band EUV emission from Sn laser-produced plasma

F. Torretti, Ruben Schupp, Dmitry Kurilovich, Alex Bayerle, Joris Scheers, Wim Ubachs, Ronnie Hoekstra, Oscar Versolato

Research output: Contribution to JournalArticleAcademicpeer-review

Abstract

We present the results of spectroscopic measurements in the extreme ultraviolet regime (7–17 nm) of molten tin microdroplets illuminated by a high-intensity 3 J, 60 ns Nd:YAG laser pulse. The strong 13.5 nm emission from this laser-produced plasma (LPP) is of relevance for next-generation nanolithography machines. Here, we focus on the shorter wavelength features between 7 and 12 nm which have so far remained poorly investigated despite their diagnostic relevance. Using flexible atomic code calculations and local thermodynamic equilibrium arguments, we show that the line features in this region of the spectrum can be explained by transitions from high-lying configurations within the Sn${}^{8+}$–Sn${}^{15+}$ ions. The dominant transitions for all ions but Sn${}^{8+}$ are found to be electric-dipole transitions towards the n = 4 ground state from the core-excited configuration in which a 4p electron is promoted to the 5s subshell. Our results resolve some long-standing spectroscopic issues and provide reliable charge state identification for Sn LPP, which could be employed as a useful tool for diagnostic purposes.
Original languageEnglish
Article number045005
JournalJournal of Physics B. Atomic, Molecular and Optical Physics
Volume51
Issue number045005
DOIs
Publication statusPublished - 25 Jan 2018

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