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11 October 2000 Evaluation of fused silica for DUV laser application by short-time diagnostics
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Excimer laser pulses ((lambda) equals 193 nm, (lambda) equals 248 nm) induce transient and permanent defects in highly UV transparent optical glass for microlithography. Usually laser damage of fused silica is evaluated by time consuming and expensive marathon tests characterized by about 109 pulses at repetition rates of 400-1000 Hz and fluences of 0.5-10 mJ/cm2. Alternatively, short time tests using high laser energy densities have been developed to quickly evaluate influences of changes in the production technology. The following evaluation methods are used: Laser induced absorption at 193 nm measured by laser induced deflection (LID), Laser induced fluorescence at 650 nm (LIF) excited by 193 nm or 248 nm laser irradiation, H2 content measurement by means of a pulsed Raman spectroscopy at 248 nm laser excitation. Both, the LIF signal and the H2 concentration are measured locally resolved in a non-destructive way. The applied energy densities of the above methods vary from 1 mJ/cm2 to 600 mJ/cm2. The front face technique for investigating large diameter samples, e.g. mask blanks (6 inches and 9 inches), have been established.
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Wolfgang Triebel, Sylvia Bark-Zollmann, Christian Muehlig, Andreas Voitsch, Frank Coriand, and Jochen Alkemper "Evaluation of fused silica for DUV laser application by short-time diagnostics", Proc. SPIE 4103, Optical Diagnostic Methods for Inorganic Materials II, (11 October 2000);

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