Design of Photoresists with Reduced Environmental Impact. 1. Water-Soluble Resists Based on Photo-Cross-Linking of Poly(vinyl alcohol)

• Published in: Chemistry of materials 1999-03, Vol.11 (3), p.719-725
• Main Authors: Havard, Jennifer M, Shim, Sang-Yeon, Fréchet, Jean M. J, Lin, Qinghuang, Medeiros, David R, Willson, C. Grant, Byers, Jeffrey D
• Format: Article
• Language: English
• Subjects: Application fields; Applied sciences; Exact sciences and technology; Polymer industry, paints, wood; Technology of polymers
• ISSN: 0897-4756; 1520-5002
• DOI: 10.1021/cm980603y

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 silicon wafers. Negative-tone images were obtained upon irradiation at 254 nm, postbaking, and subsequent development in pure water. The two-component resist suffered from swelling during development, but improved performance was obtained through the addition of a cross-linking agent, hexamethoxymethylmelamine (HMMM). The resulting three-component, water-soluble resist was able to resolve micron-sized images using a 248 nm stepper, at a dose of ca. 200 mJ/cm2. Model studies conducted using 13C NMR monitoring with 2,4-pentanediol 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.