A comprehensive study on three typical photoacid generators using photoelectron spectroscopy and abinitio calculations.

Abstract

Conducting a comprehensive molecular-level evaluation of a photoacid generator (PAG) and its subsequent impact on lithography performance can facilitate the rational design of a promising 193nm photoresist tailored to specific requirements. In this study, we integrated spectroscopy and computational techniques to meticulously investigate the pivotal factors of three prototypical PAG anions, p-toluenesulfonate (pTS-), 2-(trifluoromethyl)benzene-1-sulfonate (TFMBS-), and triflate (TF-), in the lithography process. Our findings reveal a significant redshift in the absorption spectra caused by specific PAG anions, attributed to their involvement in electronic transition processes, thereby enhancing the transparency of the standard PAG cation, triphenylsulfonium (TPS+), particularly at ∼193nm. Furthermore, the electronic stability of PAG anions can be enhanced by solvent effects with varying degrees of strength. We observed the lowest vertical detachment energy of 6.6eV of pTS- in PGMEA solution based on the polarizable continuum model, which prevents anion loss at 193nm lithography. In addition, our findings indicate gas-phase proton affinity values of 316.4 kcal/mol for pTS-, 308.1 kcal/mol for TFMBS-, and 303.2 kcal/mol for TF-, which suggest the increasing acidity strength, yet even the weakest acid pTS- is still stronger than strong acid HBr. The photolysis of TPS+-based PAG, TPS+·pTS-, generated an excited state leading to homolysis bond cleavage with the lowest reaction energy of 83 kcal/mol. Overall, the PAG anion pTS- displayed moderate acidity, possessed the lowest photolysis reaction energy, and demonstrated an appropriate redshift. These properties collectively render it a promising candidate for an effective acid producer.