Positive Photoresist Chemistry

Abstract

The present paper describes chemistry of naphthoquinone diazide (NQD) — novolak type positive photoresists focusing on the reactions of NQD. NQD is a highly reactive compound and has been known to render various kinds of reactions, among which photochemical, thermal and base catalyzed reactions are very important for the positive photoresist chemistry. Upon light exposure it releases nitrogen and undergoes Wolff rearrangement to transform into a ketene, which then reacts with water to produce an acid. This series of well-known reactions is regarded as the principle of pattern formation of the positive photoresist. Recent photochemical works seem focused on revealing more detailed mechanisms and kinetics of the reactions. Thermal and base catalyzed reactions give crosslinked structures to the resist which play important roles in several novel resist processes for improved resist performances such as deep-UV cure, REL, LENOS and DESIRE processes. The present paper elucidates the mechanisms of these processes based on the results of our model experiments on thermal and base catalyzed reactions.