Characterization of the polymer-developer interface in 193-nm photoresist polymers and formulations during dissolution

Abstract

Investigations of the dissolution behavior of the IBM V2 193 nm methacrylate photoresist polymer and its formulations using the recently developed impedance quartz-crystal microbalance methodology unequivocally confirm the presence of an interfacial gel layer during dissolution. All aspects of V2 dissolution behavior are strong functions of resist formulation, developer concentration, and resist film thermal history. The dissolution process is characterized by (a) a complex gel layer evolution regime; (b) a steady-state dissolution regime; and (c) a final gel layer decay regime upon depletion of solid resist film. The gel layer evolution regime exhibits a linear increase in mass and development of a lossy film component (interfacial gel) associated with developer uptake. The transition from this regime to the steady-state dissolution regime is accompanied by reproducible correlated excursions in frequency shift and film resistance measurements. The steady-state dissolution regime exhibits a linear decrease in mass and fairly constant gel-layer; upon depletion of the solid resist film, the gel layer decays. Absolute and relative metrics for phenomena occurring in these regimes can be extracted from the dissolution data and are useful for analyzing the influences of formulation components on dissolution and gelation behaviors. Formulation components explored include a photoacid generator, bis(t-butylphenyliodonium) perfluorobutanesulfonate, and common dissolution modifiers, t-butyl lithocholate and lithocholic acid. Film thermal history impacts dissolution phenomena strongly and appears to reflect both polymer annealing and residual solvent evaporation effects.