Influence of activation energy on LER in chemically amplified KrF photoresists

LER of an acetal-type photoresist (PR) and an annealing-type PR was measured by Atomic Force Microscopy, with which LER is more quantitatively measurable than using SEM. The annealing-type PR showed smaller LER than acetal-type did. Acid diffusion length measurement of these two types of KrF photoresists with a practical method that is a measurement of the thickness loss in a resist film after development which follows placement of exposed resist powder on the surface and applying PEB was also executed. The annealing-type PR has been found to show longer acid diffusion length than that of acetal-type PR. Considering deblocking temperature, acetal group is cleaved right upon exposure before PEB due to its relatively low activation energy. This means that there would be more hydroxystyrene units in acetal-type PR at the beginning of PEB than in annealing-type one. T-g of photoresist samples before and after deblocking reaction was also measured by DSC. After deblocking reaction, it was found that T-g of acetal-type PR is much higher than that of annealing-type PR. This relatively high T-g will make acetal-type PR to have shorter acid diffusion length in conjunction with relatively low PEB temperature comparing with annealing-type in general. The absolute T-g value and T-g change with deblocking reaction depending on types of PRs were correlated to explain the inherent difference in LER performance in different types of PRs.