Sensitized Transparent Photobase Additive For 193nm Lithography

This paper reports on the use of trimethyl sulfonium hydroxide as a base additive for 193nm applications, which is found to stabilize the latent image as well as act as a photodecomposable base. Delay time stability (exposure to post-exposure bake) of formulations consisting of trimethylsulfonium hydroxide is compared to that of a non-photodecomposable base (diethanolamine) in both methacrylate- and cycloolefin-based 193nm resists. Resist formulations made using the trimethylsulfonium base were delay-stable for more than one hour, while the reference formulation with diethanolamine showed T-top formation within 10 minutes delay time under the same conditions. The trialkylsulfonium hydroxide base additives were found to be photodecomposable by measuring the acid produced upon exposure. Compared to a non-photodecomposable base containing resist, the photodecomposable base containing resist produced more acid in the exposed areas under identical PAG/BASE molar ratios.