David Punsalan

Strategies for purging the pellicle space for 157 nm lithography

Current microlithography research is examining the viability of a 157 nm exposure wavelength in order to decrease the size of printed features. This wavelength shift is particularly challenging because many components of air strongly absorb at 157 nm, such as O2, H2O, and CO2. The particle barrier known as the pellicle presents a substantial resistance to mass transfer. In this project, a purge chamber has been devised that can decontaminate the reticle from these species. This work evaluates various purging strategies using polymeric and inorganic pellicle materials to attain acceptable contaminant levels. Results are presented that show the decline in O2 concentration over time within the pellicle space under an external N2 purge. Variables in the experiment include the pellicle material, the allotment of filters on the pellicle frame, and the flow rate of the purge gas. Furthermore, a model of the purging process was developed, which shows good agreement with experimental data.