Study of Sn removal processes for in-situ collector cleaning

Daniel T. Elg, Gianluca A. Panici, Shailendra N. Srivastava, D. N. Ruzic

Research output: Chapter in Book/Report/Conference proceedingConference contribution


An in-situ hydrogen plasma cleaning technique to clean Sn off of EUV collector optics is studied in detail. The cleaning process uses hydrogen radicals (formed in the hydrogen plasma) to interact with Sn-coated surfaces, forming SnH4 and being pumped away. This technique has been used to clean a 300mm-diameter stainless steel dummy collector optic, and EUV reflectivity of multilayer mirror samples was restored after cleaning Sn from them, validating the potential of this technology. This method has the potential to significantly reduce downtime and increase source availability. However, net Sn removal is limited by decomposition of the SnH4 molecule upon impact with the collector and the resulting redeposition of Sn. This is true in all cleaning systems that make use of hydrogen radicals. Thus, to guide the design of effective cleaning systems, the transport of Sn in the chamber, and the fundamental processes affecting it, must be understood. Accordingly, an investigation into these processes Sn removal is being performed. These processes include the advection of gas through the chamber, the creation of hydrogen radicals, the etching of Sn by radicals, and the surface decomposition of SnH4. In this paper, experiments to determine the radical density are presented, along with a theoretical plasma chemistry model that explains the processes behind radical creation and validates the radical density measurements. Additionally, experiments are shown that provide an insight into the etching of Sn by hydrogen radicals, yielding calculations of etching probability as well as showing that Sn etching is very sensitive to oxygen contamination and surface morphology.

Original languageEnglish (US)
Title of host publicationExtreme Ultraviolet (EUV) Lithography VII
EditorsEric M. Panning, Kenneth A. Goldberg
ISBN (Electronic)9781510600119
StatePublished - 2016
EventExtreme Ultraviolet (EUV) Lithography VII - San Jose, United States
Duration: Feb 22 2016Feb 25 2016

Publication series

NameProceedings of SPIE - The International Society for Optical Engineering
ISSN (Print)0277-786X
ISSN (Electronic)1996-756X


OtherExtreme Ultraviolet (EUV) Lithography VII
Country/TerritoryUnited States
CitySan Jose


  • cleaning
  • collector
  • debris
  • in-situ
  • optic
  • reflectivity

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Condensed Matter Physics
  • Computer Science Applications
  • Applied Mathematics
  • Electrical and Electronic Engineering


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