A Standard Addition Technique To Quantify Photoacid Generation in Chemically Amplified Photoresist

A technique to determine the efficiency of the decomposition of photoacid generators to produce photoacid and the concentration of acid necessary to image chemically amplified photoresists was designed, implemented, and validated. The technique is analogous to a standard addition experiment; known concentrations of a base quencher are added to a series of otherwise identical resist formulations. To produce the same free acid concentration within the resist films after neutralization, the concentration of photogenerated acid must increase by an amount equal to the known concentration of added base. The increase in exposure dose required to create this additional acid is indirectly determined as a function of base loading using resist dissolution behavior (contrast curves). The main assumptions implicit in the model to extract the Dill C parameter (a parameter proportional to the quantum yield) from experiments were validated using X-ray exposure and a positive tone photoresist system consisting of poly(p-t-butoxycarbonyloxystyrene-co-p-hydroxystyrene) as the base resin, norbornene dicarboximidyl triflate as the photoacid generator, and 1-piperidineethanol as the base quencher. Resin deprotection monitored by FTIR and dissolution rate measurements provided independent evidence that the bulk dissolution rate, the dissolution induction time, and the extent of deprotection as a function of the free acid concentration remained the same for resists with and without base.