7 July 1997 Excimer laser interactions with dielectric thin films for advanced projection optics
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Stable and efficient UV-laser systems require stable and efficient optics which can only be realized by applying high performance, low loss and highly damage resistant thin film interference coatings. The interaction between excimer laser photons and optical coatings is determined by combined effects of high repetition rates and high energy densities. Optical stability investigations on oxide and fluoride thin films have been performed to estimate ns-laser-induced- damage-thresholds. By using thermal mirage technique both the detection of the damage onset after illumination with KrF excimer laser (248 nm, 20 ns) and the exploitation of the increase of the signal per unit fluence for the interpretation of the origins of radiation damage were possible. Damage sensitive defects were identified to origin both from residual gas and evaporation sources. By optimizing electron beam evaporation technology the defect density was drastically reduced.
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Norbert Kaiser, Norbert Kaiser, Roland Thielsch, Roland Thielsch, Michael Mertin, Michael Mertin, Harry H. Bauer, Harry H. Bauer, Eberhard Welsch, Eberhard Welsch, } "Excimer laser interactions with dielectric thin films for advanced projection optics", Proc. SPIE 3051, Optical Microlithography X, (7 July 1997); doi: 10.1117/12.276050; https://doi.org/10.1117/12.276050

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