1 July 2002 Radiation-induced carbon contamination of optics
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Abstract
In this work molecular contamination of optical components such as e.g. reflective mirrors for extreme ultraviolet (EUV) lithography was experimentally studied using irradiation with keV electrons. Since secondary electrons are known to initiate most of the surface chemistry, radiation with EUV photons or electrons often gives similar results. Due to presence of hydrocarbon molecules in a vacuum system, carbon growth will occur at each irradiated surface. The carbon growth rate for various molecules was measured by in-situ Auger electron spectroscopy and Rutherford backscattering spectroscopy (RBS) analyzing the influence of the two main parameters being radiation dose and partial pressure of hydrocarbons. The latter was varied over a large range from 10-5 until 10-11 mbar. Furthermore the structure of the resulting carbon films was analyzed by X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy indicating the formation of a nanocrystalline graphite-like structure independent of the original hydrocarbon molecule.
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Ralph Kurt, Michiel van Beek, Co Crombeen, Peer Zalm, Yde Tamminga, "Radiation-induced carbon contamination of optics", Proc. SPIE 4688, Emerging Lithographic Technologies VI, (1 July 2002); doi: 10.1117/12.472279; https://doi.org/10.1117/12.472279
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