Micromolar concentrations of base quenchers impact the apparent efficiency of photoacid generation in chemically amplified resists

The chemical composition of the base quencher added to chemically amplified photoresist formulations was found to influence the apparent efficiency of processes that lead to photoacid generation upon exposure to ionizing radiation. Resists formulated with the base quencher 1-piperidineethanol (1PE) required lower exposure doses to render development than resists containing 3-piperidino-1,2-propanediol (3P12PD) as the base. A standard addition technique was employed to determine the efficiency of photoacid generation in resist formulations consisting of one of the two base quenchers, the photoacid generator triphenylsulfonium triflate, and a matrix polymer composed of primarily p-hydroxystyrene and tert-butylacrylate monomers (environmentally stable chemically amplified photoresist type). The resist containing 1PE exhibited an apparently greater efficiency for photoacid generation than the formulation containing 3P12PD. Analysis of development processes showed that resists containing these bases exhibited identical dissolution behavior to that of a system without base quencher, verifying that resist dissolution could not explain the difference in exposure dose required for development of the 1PE and 3P12PD resists. Furthermore, the action of photoacid to deprotect the polymer, as interpreted from infrared spectroscopy, and the concentration of photoacid required to render development were the same for both resists. These results suggest that the small concentration of base in the resist may participate in the complicated chemical processes that produce photoacid from the decomposition of PAG upon exposure to ionizing radiation.