Dissolution inhibition produced by diazonaphthoquinones in novolak and in other phenolic resins is based on the formation of phenolic clusters. The principal result of the exposure of novolak-diazoquinone resist films to light is the dispersal of these clusters. It occurs through the thermal effect of the Wolff rearrangement that follows the photolysis of diazonaphthoquinone. Indenecarboxylic acid, which is the final product of irradiation, is converted to indenecarboxylate ion in the penetration zone of the dissolving films, where it adds to the concentration of hydrophilic percolation sites. This causes the dissolution rate of exposed resist films to be accelerated above that of pure novolak.