Properties and performance of EUVL pellicle membranes

Abstract

EUV mask protection during handling and exposure remains a challenge for high volume manufacturing using EUV scanners. A thin, transparent membrane can be mounted above the mask pattern so that any particle that falls onto the front of the mask is held out of focus and does not image. The fluoropolymer membranes that are compatible with 193nm lithography absorb too strongly at the 13.5nm EUV exposure wavelength to be considered. Initially, the industry planned to expose EUV masks without any pellicle; however, the time and cost of fabricating and qualifying an EUV mask is simply too high to risk decimating wafer yield each time a particle falls onto the mask pattern. Despite the challenges of identifying a membrane for EUV, the industry has returned to the pellicle concept for protection. EUVL pellicles have been in development for more than a decade and reasonable options exist. Meeting all pellicle requirements is difficult, so this type of risk-mitigation effort is needed to ensure that there is a viable high-volume manufacturing option. This paper first reviews the desired membrane properties for EUVL pellicles. Next, candidate materials are introduced based on reported properties and compatibility with fabrication. Finally a set of candidate membranes are fabricated. These membranes are screened using a simplified set of tests to assess their suitability as an EUV pellicle. EUV transmission, film stress, and film durability data are included. The results are presented along with general guidelines for pellicle membrane properties for EUV manufacturing.