Photochemically-induced acid-catalyzed polymer reactions for microlithography

Abstract

This paper reviews our work on acid-catalyzed deprotection and depolymerization reactions for the design of chemically amplified resist systems. AAL-1 acidolysis can be conveniently used to design dual tone resist systems that can be developed in either a positive or a negative mode depending on the polarity of the developer solvent, which is due to conversion of lipophilic polymers to acidic polymers. Such deprotection reactions also allow selective silylation of the acidic polymers formed in the exposed regions, providing negative dry development by O2 reactive ion etching (RIE). Thermal and acid-catalyzed deesterification and rearrangement of cyclopropyl carbinol esters can be exploited in the design of negative resist systems that can be developed either with anisole or with aqueous base depending on the postexposure bake temperature. Acid-catalyzed desterification of poly(α-acetoxystyrene) results in formation of poly(phenylacetylene) and simultaneous depolymerization, providing a positive resist system. Positive resist systems based on acid-catalyzed depolymerization of polyphthalaldehyde (PPA) derivatives include a thermally developable O2 RIE barrier resist and the use of PPA as a dissolution inhibitor for a novolac resin. A very efficient depolymerization of poly(p-hydroxy-α-methylstyrene) (p-PIIOMS) initiated by reaction of its end group with acids is also discussed as a third mode of depolymerization.