PHOTOACID BULKINESS ON DISSOLUTION KINETICS IN CHEMICALLY AMPLIFIED DEEP-ULTRAVIOLET RESISTS

The photoacid bulkiness effect on dissolution characteristics was inve stigated in a three-component chemically amplified deep ultraviolet po sitive 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 bi sphenol A). For the benzenesulfonic acid photoacid generator, four typ es 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 bulki ness. The reason for this is that bulky substituents such as 2,4-dimet hyl and 4-tert-butyl increased resist hydrophobic strength in both bul k and surface regions, thereby strengthening the surface inhibition ef fect. Next, in order to investigate the bulkiness effect on acid mobil ity, diffusion length during postexposure bake time was determined by means of the ion conductivity method. Diffusion length decreased and r esist 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 cas e of a shorter diffusion length, Therefore, the surface inhibition eff ect becomes strong, and then the T-topping profile was observed in 4-t ert-butyl substituent. In order to understand the details of surface i nhibition effect, resist pattern profile simulation was carried out us ing PROLITH/2 version 3.0. Simulation results of pattern profiles coin cided with the actual resist pattern by adjusting the parameters of th e surface inhibition effect (relative surface rate and inhibition dept h). It was found that the photoacid bulkiness effect on pattern profil es can be explained by the surface inhibition effect. Based on the ana lysis of the dissolution characteristics, acid diffusion behavior and profile simulation, it was concluded that Me resist pattern profile, e specially its top rectangularity, can be controlled by changing the su bstituent group of photogenerated benzenesulfonic acid. By combining t he modification of the base resin structure (protection ratio and mole cular weight) and acid structures, both high resolution capability and rectangular resist pattern profiles can be achieved. (C) 1995 America n Vacuum Society