Applications of Photoinitiators to the Design of Resists for Semiconductor Manufacturing

Acids generated via radiolysis of cationic photoinitiators, such as aryldiazonium, diaryliodonium, and triarylsulfonium metal halides can induce a variety of chain reactions in polymers, including (1) cross-linking, (2) catalytic deprotection, and (3) catalytic depolymerization. All of these reactions can be exploited in the design of resist materials. When formulated with the onium salt photoinitiators, (1) epoxy resins undergo efficient cross-linking reactions to provide negative tone resists; (2) poly(p-t-butoxy carbonyloxystyrene) is converted to poly(p-hydroxystyrene) in the exposed areas to provide either a positive or negative resist tone depending on the developer employed; and (3) polyaldehydes are completely reverted to monomer upon exposure and vaporize during the exposure to provide self-developing positive resists. The extremely high sensitivity of these systems is achieved through chemical amplification.