A critical issue leading to decreased mirror lifetime is the buildup of debris on the surface of the primary mirror optics that comes from the use of both Sn and Li in GDPP or LPP. While lithium can easily be evaporated from the optic surface initially, over long duration high volume manufacturing, it is experimentally observed that there can be lithium debris buildup on the optic surfaces, which can lead to shortened lifetime of the mirror optics and decreased productivity of the tool. Consequently, an in situ cleaning process is needed so as to remove and limit the surface contamination on the optics so as to extend the lifetime of the optics. The Surface Cleaning of EUV Optics by Plasma Exposure (SCOPE) experiment was developed to study the mechanism of lithium deposition and the resulting diffusion to the end goal of using a secondary plasma source to preferentially remove the lithium surface contamination while leaving the underlying optic matrix in tact. Results have shown preferential lithium debris mitigation and sputtering from the surface of the MLM optic materials through the use of a secondary plasma that does not interfere or absorb EUV photons.

Date Published: 18 January 2007
PDF: 8 pages
Proc. SPIE 6151, Emerging Lithographic Technologies X, 615132 (18 January 2007); doi: 10.1117/12.656614

Published in SPIE Proceedings Vol. 6151:
Emerging Lithographic Technologies X
Michael J. Lercel, Editor(s)