The Multifunctional Role of Base Quenchers in Chemically Amplified Photoresists

A systematic investigation of four base quenchers in chemically amplified photoresist revealed that the role of the base quencher is more complex than rapid, stoichiometric neutralization of photoacid. The base quenchers studied included common supplements to chemically amplified photoresist, 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), 1-piperidineethanol (1PE), and tetrabutylammonium hydroxide (TBAH), and an atmospheric contaminant and poison to chemically amplified resists, N-methyl pyrrolidinone (NMP). Acid−base neutralization, deprotection, and development processes in formulations with and without base quencher were evaluated to determine the effects of the base quencher on resist processing. The extent of deprotection of the polymer was measured by infrared spectroscopy and analyzed as a function of the concentration of photoacid within the resist. The concentration of photoacid after exposure was determined using a standard addition technique that quantified the efficiency of photoacid generation. Dissolution rates were measured as a function of the extent of deprotection, and the induction time during development was measured as a function of the resist dissolution rate. Some base quenchers were found (i) to neutralize photoacid in the resist with less than stoichiometric proportions, (ii) to act as dissolution inhibitors or promoters, and (iii) to lengthen the induction time during development. These results show that base quenchers act in considerably more complex ways than the stoichiometric neutralization of photogenerated acid, and understanding these multifunctional characteristics is important for the design of improved resist systems for high-resolution lithography.