Plasma Chemistry and Plasma Processing

, Volume 38, Issue 1, pp 223–245 | Cite as

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
Original Paper


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.


EUV Sn Etching Reactive ion etching Collector Cleaning In-situ Plasma Hydrogen SnH4 Decomposition 



This material is based upon work supported by the National Science Foundation under Grant No. 14-36081. Additionally, the authors are grateful for funding and support from Cymer, LLC, an ASML company. The authors would also like to thank undergraduate students Sean Piper, Shubhang Goswami, Luke Gasparich, Shanna Bobbins, and Andreas Giakas for their help in carrying out experiments. Parts of this research were carried out in the Frederick Seitz Materials Research Laboratory Central Facilities, University of Illinois, which is partially supported by the U.S. Department of Energy under Grants DEFG02-07ER46453 and DE-FG02-07ER46471.


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Copyright information

© Springer Science+Business Media, LLC 2017

Authors and Affiliations

  • Daniel T. Elg
    • 1
    • 4
    • 5
  • Gianluca A. Panici
    • 1
  • Sumeng Liu
    • 2
  • Gregory Girolami
    • 2
  • Shailendra N. Srivastava
    • 3
  • David N. Ruzic
    • 1
  1. 1.Department of Nuclear, Plasma, and Radiological Engineering, Center for Plasma-Material InteractionsUniversity of Illinois at Urbana-ChampaignUrbanaUSA
  2. 2.Department of ChemistryUniversity of Illinois at Urbana-ChampaignUrbanaUSA
  3. 3.Applied Research InstituteUniversity of Illinois at Urbana-ChampaignChampaignUSA
  4. 4.Department of Chemical and Biomolecular EngineeringUniversity of California, BerkeleyBerkeleyUSA
  5. 5.Applied Materials, Inc.Santa ClaraUSA

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