ABSTRACT
Negative tone resists based on acid-hardening resin chemistry are three-component systems composed of a novolac resin, a melamine crosslinking agent, and a radiation-sensitive acid generator. The copolymerization chemistry of maleic anhydride/cyclic olefin polymers was less well established than that of the methacrylate polymerization used to prepare methacrylate co- and terpolymers. Halogen compounds such as trichloromethyl-s-triazene have been known as free-radical initiators for photopolymerization. The photogenerated acid induces depolymerization of polyphthalaldehyde, resulting in loss of dissolution-inhibition capability to give a positive image. The workers of Hoechst AG reported three-component chemical-amplification resist systems using acid-catalyzed depolymerization of O,O- and N,O-acetals. The chain-reaction character of the epoxy group in acid-catalyzed ring-opening polymerization can be used to obtain negative resists. The simple, straightforward polymerization produces a corresponding material that is quite simple, with a narrow molecular-weight distribution. The material is based on simple, direct terpolymerization of methacrylate monomers, with no postpolymerization reactions as commonly found in 248 nm materials.
