Polyelectrolyte effects in model photoresist developer solutions: Roles of base concentration and added salts

Abstract

We demonstrate that poly(4-hydroxystyrene) and (5, 15, and 20) % tert-butoxycarboxy protected copolymers are polyelectrolytes when dissolved in aqueous base solutions. The polyelectrolyte effect is quantified through the observation of a correlation peak, measured with small-angle neutron scattering. Polyelectrolyte effects are weakened with added salts and excess base. These studies emphasize that salt additives screen the electrostatic interactions, while pH leads to the ionization of the chain. Solvent quality is quantified and the chain configurations are measured in the limit of high ionic strength. It is speculated that the developer-resist interactions will play an important role in development-induced roughness, hence these equilibrium solution measurements can serve a predictive function for future photoresists dissolution models incorporating solvent quality as a parameter.