Comparison of H2 and He carbon cleaning mechanisms in extreme ultraviolet induced and surface wave discharge plasmas

A. Dolgov, D. Lopaev, T. Rachimova, A. Kovalev, A. Vasilyeva, Christopher James Lee, V.M. Krivtsun, O. Yakushev, Frederik Bijkerk

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Abstract

Cleaning of contamination of optical surfaces by amorphous carbon (a-C) is highly relevant for extreme ultraviolet (EUV) lithography. We have studied the mechanisms for a-C removal from a Si surface. By comparing a-C removal in a surface wave discharge (SWD) plasma and an EUV-induced plasma, the cleaning mechanisms for hydrogen and helium gas environments were determined. The C-atom removal per incident ion was estimated for different sample bias voltages and ion fluxes. It was found that H2 plasmas generally had higher cleaning rates than He plasmas: up to seven times higher for more negatively biased samples in EUV induced plasma. Moreover, for H2, EUV induced plasma was found to be 2-3 times more efficient at removing carbon than the SWD plasma. It was observed carbon removal during exposure to He is due to physical sputtering by He+ ions. In H2, on the other hand, the increase in carbon removal rates is due to chemical sputtering. This is a new C cleaning mechanism for EUV-induced plasma, which we call "EUV-reactive ion sputtering".
Original languageEnglish
Article number065205
Pages (from-to)-
Number of pages9
JournalJournal of physics D: applied physics
Volume47
Issue number6
DOIs
Publication statusPublished - 2014

Keywords

  • IR-88098
  • METIS-299269

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