Positive tone dry-develop resist based on cross-linking a phenolic resin

Abstract

We have previously shown that a copolymer of p-hydroxystyrene and p-acetoxymethylstyrene can be used as a sensitive deep UV resist. In that study we demonstrated that a formulation of this copolymer and an onium salt could be exposed, baked and developed in aqueous base to yield a high resolution negative tone relief image. In this paper we will discuss a gas phase silylation process that converts this negative tone solvent-developable resist system, into a positive tone dry-developable resist system. We have used an FT-IR microscope, coupled to a motorized X-Y stage, to study the silylation process as a function of UV exposure dose and silylation processing parameters. By altering the copolymer ratio, we found that resist contrast increased when the amount of acetoxymethyistyrene increased. This resist system and dry develop process were used to print 0.35 j.m images at a DUV dose of approximately 25 mJ/cm2.