How to make polyvinylphenol inhibitable by diazonaphthoquinone sulfonates

There is interest in phenolic resins that are transparent at 248 nm and the dissolution of which in alkaline aqueous developers can be inhibited by diazonaphthoquinone sulfonic acid derivatives, the standard photoactive compounds (PACs) of novolak resists. Poly(4-hydroxystyrene), i.e., poly(vinylphenol), has the requisite optical properties, but its dissolution is not very effectively inhibited by standard PACs. We have now found that poly(4-hydroxystyrene) can be made more inhibitable by increasing the acidity of its OH groups and, at the same time, lowering the concentration of the acidic OH groups in the resin.