Effect of photoacid generator concentration on sensitivity, photoacid generation, and deprotection of chemically amplified resists

Abstract

The dependence of resist processes (sensitivity, efficiency of photoacid generation, polymer deprotection) on the concentration of the photoacid generator (PAG) in formulations of chemically amplified photoresist was investigated as a function of the concentration of photoacid that was generated upon exposure. Although the sensitivity of a photoresist formulation improved by increasing the concentration of PAG in the resist formulation, the concentration of photoacid required to achieve an appropriate extent of deprotection to render development also increased. Using a standard addition technique, the efficiency of photoacid generation was quantified for resist systems consisting of triphenylsulfonium triflate as the PAG in an environmentally stable chemically amplified photoresist-type polymer primarily composed of 4-hydroxystyrene and tert-butyl acrylate monomers. Determination of the apparent efficiency of photoacid generation (the resist C parameter) allowed the concentration of photoacid within the resist film to be calculated for any exposure dose. Deprotection of the polymer was measured using infrared spectroscopy and analyzed as a function of the photoacid concentration within the resist. We determined from these results that the increase in the concentration of photoacid required for development of the resist was caused by a change in the deprotection process during the postexposure bake and was not due to dissolution inhibition by the unexposed PAG.