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Proceedings Article

Long-term 193-nm laser irradiation of thin-film-coated CaF2 in the presence of H2O

[+] Author Affiliations
V. Liberman, M. Switkes, M. Rothschild, S. T. Palmacci, J. H. C. Sedlacek, D. E. Hardy

Lincoln Lab., Massachusetts Institute of Technology (USA)

A. Grenville

Intel Corp./International SEMATECH (USA)

Proc. SPIE 5754, Optical Microlithography XVIII, 646 (May 12, 2005); doi:10.1117/12.601468
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From Conference Volume 5754

  • Optical Microlithography XVIII
  • Bruce W. Smith
  • San Jose, CA | February 27, 2005

abstract

The final projection lens element in a 193-nm immersion-based lithographic tool will be in direct contact with water during irradiation. Thus, any lifetime considerations for the lens must include durability data of lens materials and thin films in a water ambient. We have previously shown that uncoated CaF2 is attacked by water in a matter of hours, as manifested by a substantial increase in AFM-measured surface roughness.1 Thus, CaF2 lenses must be protected, possibly by a thin film, and the coatings tested for laser durability in water. To address the above lifetime concerns, we have constructed a marathon laser-irradiation system for testing thin film exposure to water under long-term laser irradiation. Coated substrates are loaded into a custom water cell, made of stainless steel and Teflon parts. Ultrapure water is delivered from a water treatment testbed that includes particle filtration, deionization and degassing stages. In-situ metrology includes 193-nm laser ratiometry, UV spectrophotometry and spectroscopic ellipsometry, all with spatial profiling capabilities. In-situ results are coupled with off-line microscopy, AFM measurements and spatial surface mapping with spectroscopic ellipsometry at multiple incidence angles. A variety of laser-induced changes have been observed, from complete adhesion loss of protective coatings to more subtle changes, such as laser-induced index changes of the thin films or surface roughening. Implications of the study on expected lifetimes of the protective coatings in the system will be discussed.

© (2005) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
Citation

V. Liberman ; M. Switkes ; M. Rothschild ; S. T. Palmacci ; J. H. C. Sedlacek, et al.
"Long-term 193-nm laser irradiation of thin-film-coated CaF2 in the presence of H2O", Proc. SPIE 5754, Optical Microlithography XVIII, 646 (May 12, 2005); doi:10.1117/12.601468; http://dx.doi.org/10.1117/12.601468


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