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28 May 2004 Photo-induced changes in 157-nm optical coatings
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The photo-induced degradation of 157-nm anti-reflective (AR) coatings, and the role of water vapor in the ambient, have been studied with in-situ spectroscopic ellipsometry, atomic force microscopy (AFM), and x-ray photoelectron spectroscopy. Using ellipsometric techniques, we find that MgF2 thin films develop a surface roughness layer under laser irradiation at an incident dose of ~0.1 MJ/cm2. These thin film changes occur well before any changes in 157-nm transmission are observed. The findings are confirmed by ex-situ post-irradiation AFM measurements. LaF3 does not exhibit this effect. Addition of ppm-levels of moisture suppresses surface roughness formation, suggesting that the surface roughness growth may be a precursor to the transmission degradation of full AR stacks that had been observed earlier.
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Vladimir Liberman, Theodore M. Bloomstein, Mordechai Rothschild, Stephen T. Palmacci, Jan H. C. Sedlacek, and Andrew Grenville "Photo-induced changes in 157-nm optical coatings", Proc. SPIE 5377, Optical Microlithography XVII, (28 May 2004);

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