Design of New Positive-Tone Photoresists Based on the Acid-Catalyzed Hydrolysis of Phenylmethanediol Diesters

A series of novel phenylmethanediol diesters have been designed for use as dissolution inhibitors of phenolic resins in alkaline solution. The rates of triflic acid-catalyzed hydrolyses of these gem diesters to carboxylic acids in DMSO have been measured and correlated with their structural features. New three-component positive-tone photoresists consisting of these dissolution inhibitors, a photochemical generator of acid, and poly(4-hydroxystyrene) have been prepared and tested successfully. A 20 wt % loading of the additive effectively retards the dissolution of the phenolic resin in aqueous base developer. Following exposure to radiation and the application of heat, the photogenerated acid catalyzes the decomposition of the additive to afford two molecules of a carboxylic acid that act as dissolution promoters for the polymer. The reaction temperature has a drastic influence on the dissolution properties of the resist coatings. Optimization of the processing conditions can be facilitated by ¹H NMR analyses of processed resist materials. The resists have demonstrated high sensitivities with both deep-UV (<1 mJ/cm²) and electron-beam radiation (ca. 1.7 μC/cm²).