Evaluation of Pure Novolak Cresol‐Formaldehyde Resins for Deep U.V. Lithography

A series of pure, isomeric cresol‐formaldehyde novolak resins have been synthesized and evaluated with respect to their utility as matrix resins for deep u.v. resist formulations. One of the cresols, the p‐isomer, provides a resin which has far greater optical transmission at 254 nm than the commercial cresylic acid novolaks used to formulate the classical positive photoresists. Synthetic procedures were developed which allow reproducible preparation of the p‐cresol novolak over a wide range of molecular weights including that region which displays base dissolution kinetics that are compatible with lithographic processing.