Polymeric base additives for lithographic improvement in DUV resist system

Recently, base additives have become indispensable ingredients in high resolution chemically amplified resists. These bases act as acid scavengers to extend shelf Life for low activation systems such as ketal and acetal protected polyhydorxystyrene (PHS) type resists. They are also used to improve contamination resistance for high activation resist systems such as TBOC and t-butyl ester containing resins. Studies have also shown that base additives can reduce (or eliminate) linewidth slimming and FEB sensitivity for acetal systems. Actually, one of the most important benefits of base additives is to limit acid diffusion and enhance chemical contrast during exposure and bake process, hence improving resolution and process latitudes. In this paper, we show that polymeric bases provide better lithe performance than small compounds. In addition, hydroxides are found to be better than carboxylate salts and amines.