THERMAL-STABILITY OF SULFONATE ESTER PHOTOACID GENERATORS IN PHENOLIC MATRICES

Sulfonate esters have been used extensively as photoacid generators (PAGs) in a number of chemically amplified photoresist systems. For these molecules to be useful in such systems, they must be able to withstand processing temperatures of up to 150 degrees C. Differential scanning calorimetry and thermogravimetric analysis have been used to investigate the thermal stability of a variety of classes of sulfonate esters. It has been discovered that the decomposition temperatures of a number of sulfonate esters are changed when placed in a polymeric matrix. In phenolic polymers a destabilization was observed, and in many cases the effect is profound. The thermal stability of various sulfonates including pyrogallol esters, nitrobenzyl derivatives and imino sulfonates were investigated in poly(4-hydroxystyrene) (PHS). It has been shown that acid is formed upon decomposition. Further, model reactions have been employed to investigate the mechanism of decomposition. It was concluded that both steric hindrance of the sulfonate ester linkage and the electronic effects of the functional groups on the sulfonate moiety play important roles in the thermal stability of these molecules in PHS. Finally, the effect of thermally generated acid from these photoacid generators on a typical chemically amplified resist system was studied by thermogravimetric analysis and FTIR.