Toward controlled resist line edge roughness: Material origin of line edge roughness in chemically amplified positive-tone resists

Abstract

Material origin of resist line edge roughness (LER) in positive-tone chemically amplified resists has been investigated by designing experiments to mimic the composition and the morphology of the resists in the line edge regions where the resist consists of both the protected polymer and its de-protected counterparts. Blends of the protected and the de-protected base polymers for two silicon containing, positive-tone chemically amplified resists were prepared. Morphology and surface roughness of thin films of the polymer blends were probed with atomic force microscope (AFM). AFM results clearly showed that the protected polymer and its de-protected counterparts form distinct phase separated morphology after spin coating and baking. This phase separation leads to surface roughening of the blend films. Furthermore, the surface roughness of the blend films is enhanced after development with an aqueous TMAH developer. These results suggest that the material origin of resist LER in positive-tone chemically amplified resists stems from the compositional heterogeneity due to phase incompatibility of the protected base polymer and its de-protected counterparts in the line edge regions. The effects of blend composition, the extent of de-protection, and processing conditions on the morphology and surface roughness will be presented. The implications of these findings for high-resolution resist design will also be discussed.