26 June 2003 Contamination rates of optical surfaces at 157 nm: impurities outgassed from construction materials and from photoresists
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Abstract
Photo-induced contamination rates on 157-nm optical surfaces have been studied in controlled experiments with contaminants containing fluorocarbon, sulfur and iodine. The compounds investigated represent species generated in controlled outgassing studies of common construction materials and photoresists used in 157 nm steppers. No photocontamination was measured for highly fluorinated alkanes and ethers on an anti-reflective coating, at levels exceeding 10 ppm. Photocontamination with sulfur based compounds was similar to the behavior observed with hydrocarbon based derivatives. Sulfur containing residues, even from oxidized precursors, are fully cleanable in oxygen, with cleaning rates scaling proportionally with the level of oxygen. In contrast, at elevated levels of oxygen, non-volatile iodate complexes can form from iodine based contaminants. Sulfonium salts should therefore be considered over iodonium species in photoacid generators in 157 nm photoresists. In addition to studying these new classes of compounds, cleaning rates of hydrocarbon residues in trace levels of water were also studied.
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Theodore M. Bloomstein, Jan H. C. Sedlacek, Stephen T. Palmacci, Dennis E. Hardy, Vladimir Liberman, Mordechai Rothschild, "Contamination rates of optical surfaces at 157 nm: impurities outgassed from construction materials and from photoresists", Proc. SPIE 5040, Optical Microlithography XVI, (26 June 2003); doi: 10.1117/12.485468; https://doi.org/10.1117/12.485468
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