Influence of Acid Diffusion Length on Line Edge Roughness in KrF Photoresists

LER of an acetal-type photoresist (PR) and an annealing-type PR was measured by Atomic Force Microscopy. The annealing-type PR showed smaller LER than acetal- type did. From acid diffusion length measurement study, the annealing-type PR has been found to show longer acid diffusion length than that of acetal-type PR. Considering deblocking temperature of acetal- and annealing-type PR, there would be more hydroxystyrene units in acetal-type PR at the beginning of PEB than in annealing-type one. From Tg study using DSC, it was found that Tg of acetal-type PR is much higher than that of annealing-type PR after deblocking reaction and Tg change in annealing-type PR is larger than acetal-type. The absolute Tg value and Tg change with deblocking reaction depending on types of PRs were correlated to explain the inherent difference in LER performance in different types of PRs.