A Water-Castable, Water-Developable Chemically Amplified Negative-Tone Resist

This paper describes an "environmentally friendly", water-castable, water-developable photoresist system. The chemically amplified negative-tone resist system consists of three water-soluble components: a polymer, poly(methyl acrylamidoglycolate methyl ether), [poly(MAGME)]; a photoacid generator, (2,4-dihydroxyphenyl)dimethylsulfonium triflate, and a cross-linker, 1,4-butanediol. In the three-component resist system, the acid generated by photolysis of the photoacid generator catalyzes the cross-linking of poly(MAGME) in the exposed regions during postexposure baking, thus rendering the exposed regions insoluble in water. Negative-tone relief images are obtained by developing with pure water. The resist is able to resolve 1 μm line/space features (1:1 aspect ratio) with a deep-UV exposure dose of 100 mJ/cm2 (dose to print). The resist can be used to generate etched copper relief images on printed circuit boards using aqueous sodium persulfate as the etchant. The mechanism of cross-linking has been investigated by model compound studies using 13C NMR.