The cost of ownership of semiconductor manufacturing equipment is typically addressed in terms of raw utility
consumption. Focusing on energy, the average consumption of a typical semiconductor fabrication plant has doubled
over a recent 10 year period, with approximately 30% of this energy currently attributed to vacuum equipment.
Compared to conventional optical lithography, extreme ultraviolet lithography (EUVL) requires the adoption of a
vacuum subsystem to enable the technology, bringing an additional vacuum requirement to semiconductor fabs. With
this trend it is increasingly important to focus on more efficient ways of operating semiconductor manufacturing tools
and their supporting equipment. Clever operation through employment of 'GREEN' modes can provide significant utility
savings. However, in semiconductor lithography, tool uptime is a critical parameter to be considered in any cost of
ownership model, and the facility vacuum equipment plays an intimate role here, so including redundancy in pumping
equipment can be a key enabler to maintaining tool uptime. Consequently optimizing the design of the vacuum
subsystem will help to reduce the overall footprint, utility consumption and energy costs associated with this process.
Optics contamination is a concern for extreme ultraviolet (EUV) lithography. To protect EUV optics, all materials used
in EUV vacuum exposure chambers must be screened prior to use. Photoresists are a concern since a freshly coated
wafer will be introduced into the chamber approximately every minute in a high volume production tool. SEMATECH
and the International EUV Initiative (IEUVI) have begun a resist outgassing benchmarking experiment to compare
different outgassing methodologies. Samples of the same batch of resist were sent to eight researchers. The results show
a large variation of four orders of magnitude in the amount of measured outgassing products. The next steps are to
correlate outgassing measurements to witness plate experiments.
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.