Design of photoresists with reduced environmental impact. 1. Water-solubleresists based on photo-cross-linking of poly(vinyl alcohol)

The feasibility of a chemically amplified fully water-soluble negative-tone resist based upon the cross-linking of a poly(vinyl alcohol) (PVA) matrix resin has been demonstrated. Two-component resists incorporating PVA and (2 ,4-dihydroxyphenyl)dimethylsulfonium triflate as a water-soluble photoacid generator were formulated in deionized water and spin-coated onto bare sili con wafers. Negative-tone images were obtained upon irradiation at 254 nm, postbaking, and subsequent development in pure water. The two-component res ist suffered from swelling during development, but improved performance was obtained through the addition of a cross-linking agent, hexamethoxymethylm elamine (HMMM). The resulting three-component, water-soluble resist was abl e to resolve micron-sized images using a 248 nm stepper, at a dose of ca. 2 00 mJ/cm(2). Model studies conducted using C-13 NMR monitoring with 2,4-pen tanediol as a model for PVA showed that under acidic catalysis HMMM reacts to form active electrophilic species that add to the diol, affording ether linkages with concomitant liberation of methanol.