Removal of Tin from Extreme Ultraviolet Collector Optics by In-Situ Hydrogen Plasma Etching

Daniel T. Elg, Gianluca A. Panici, Sumeng Liu, Gregory Girolami, Shailendra N. Srivastava, David N. Ruzic

Research output: Contribution to journalArticlepeer-review


Extreme ultraviolet (EUV) lithography produces 13.5 nm light by irradiating a droplet of molten Sn with a laser, creating a dense, hot laser-produced plasma and ionizing the Sn to the + 8 through + 12 states. An unwanted by-product is deposition of Sn debris on the collector optic, which focuses the EUV light emitting from the plasma. Consequently, collector reflectivity is degraded. Reflectivity restoration can be accomplished by means of Sn etching by hydrogen radicals, which can be produced by an H2 plasma and etch the Sn as SnH4. It has previously been shown that plasma cleaning can successfully create radicals and restore EUV reflectivity but that the Sn removal rate is not necessarily limited by the radical density. Additionally, while Sn etching by hydrogen radicals has been shown by multiple investigators, quantification of the mechanisms behind Sn removal has never been undertaken. This paper explores the processes behind Sn removal. Experiments and modeling show that, within the parameter space explored, the limiting factor in Sn etching is not radical flux or SnH4 decomposition, but ion energy flux. Thus the removal is akin to reactive ion etching.

Original languageEnglish (US)
Pages (from-to)223-245
Number of pages23
JournalPlasma Chemistry and Plasma Processing
Issue number1
StatePublished - Jan 1 2018


  • Cleaning
  • Collector
  • Decomposition
  • EUV
  • Etching
  • Hydrogen
  • In-situ
  • Plasma
  • Reactive ion etching
  • Sn
  • SnH

ASJC Scopus subject areas

  • Chemistry(all)
  • Chemical Engineering(all)
  • Condensed Matter Physics
  • Surfaces, Coatings and Films


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