Pushing extreme ultraviolet lithography development beyond 22 nm half pitch

Abstract

Microfield exposure tools (METs) have and continue to play a dominant role in the development of extreme ultraviolet resists and masks. One of these tools is the SEMATECH Berkeley 0.3 numerical aperture (NA) MET. Here, the authors investigate the possibilities and limitations of using the 0.3 NA MET for sub-22-nm half-pitch development. They consider mask resolution limitations and present a method unique to the centrally obscured MET, allowing mask patterning resolution limitations to be overcome. The method, however, comes at the cost of increased sensitivity to mask surface roughness. They also explore projection optics resolution limits and describe various illumination schemes allowing resolution enhancement. At 0.3 NA, the 0.5k1 factor resolution limit is 22.5 nm, meaning that conventional illumination is of limited utility for sub-22-nm development. In general, resolution enhancing illumination encompasses increased coherence. They study the effect of this increased coherence on line-edge roughness (LER), which, along with resolution, is another crucial factor in sub-22-nm resist development. Due to coherence induced LER limitations, addressing the development at 16 nm half pitch and beyond will ultimately require higher NA systems.