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20 May 2004 Short-term vacuum outgassing measurements with application to load-locks and photoresist
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Outgassing of water and hydrocarbon (CxHy) species at short timescales, ~1 minute or less, is an important technological problem when considering contamination in load-locks of extreme ultra-violet lithography (EUVL) production tools, where throughputs of 50-120 wafers/hour are required. In addition EUV stimulated outgassing will be an important property of photo-resist materials for EUV lithography, where tight control of contaminant partial pressures around the projection optics is required to preserve multilayer mirror life. The level, particularly of stimulated outgassing in the short term, has the potential to greatly influence the design of EUVL vacuum systems and contamination mitigation schemes. We have used 2 techniques to measure outgassing rates in the short term: Pressure rise method where sub 1-minute outgassing rates of a mock load-lock assembly have been measured, both empty and with silicon wafers in place; Quasi steady-state measurement where samples are quickly transferred from atmosphere to ultra-high vacuum (UHV) pressures, such that the measurement of outgassing is conducted under conditions of near-constant total pressure. We have initially used this method to measure the short term outgassing from carbon steel. In both experiments the measured outgassing rates are significantly lower than those calculated by extrapolating back from a 1 hour measurement.
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Anthony M. Keen and Neil Condon "Short-term vacuum outgassing measurements with application to load-locks and photoresist", Proc. SPIE 5374, Emerging Lithographic Technologies VIII, (20 May 2004);

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