Photoacid bulkiness on dissolution kinetics in chemically amplified deep ultraviolet resists

The photoacid bulkiness effect on dissolution characteristics was investigated in a three-component chemically amplified deep ultraviolet positive resist system. The resist consisted of a tert-butoxycarbonyl (t-BOC) protected polystyrene, benzenesulfonic acid derivative photoacid generator and an additional dissolution inhibitor (t-BOC protected bisphenol A). For the benzenesulfonic acid photoacid generator, four types of substituents; 4-fluoro, 4-chloro, 2,4-dimethyl, and 4-tert-butyl, were studied. Dissolution contrast (R(max)/R(min)) increased and the pattern profiles became rectangular with increasing substituent bulkiness. The reason for this is that bulky substituents such as 2,4-dimethyl and 4-tert-butyl increased resist hydrophobic strength in both bulk and surface regions, thereby strengthening the surface inhibition effect. Next, in order to investigate the bulkiness effect on acid mobility, diffusion length during postexposure bake time was determined by means of the ion conductivity method. Diffusion length decreased and resist profiles became rectangular with increasing photoacid bulkiness, and T-topping profile was observed in 4-tert-butyl substituent. It is believed that the acid catalytic reaction number decreases in the case of a shorter diffusion length, Therefore, the surface inhibition effect becomes strong, and then the T-topping profile was observed in 4-tert-butyl substituent. In order to understand the details of surface inhibition effect, resist pattern profile simulation was carried out using PROLITH/2 version 3.0. Simulation results of pattern profiles coincided with the actual resist pattern by adjusting the parameters of the surface inhibition effect (relative surface rate and inhibition depth). It was found that the photoacid bulkiness effect on pattern profiles can be explained by the surface inhibition effect. Based on the analysis of the dissolution characteristics, acid diffusion behavior and profile simulation, it was concluded that Me resist pattern profile, especially its top rectangularity, can be controlled by changing the substituent group of photogenerated benzenesulfonic acid. By combining the modification of the base resin structure (protection ratio and molecular weight) and acid structures, both high resolution capability and rectangular resist pattern profiles can be achieved. (C) 1995 American Vacuum Society