Diphenyliodonium 9,10-dimethoxyanthracene-2-sulfonate is photochemically dissociated to give 9,10-dimethoxyanthracene-2-sulfonic acid. The dissociation is considered to proceed via an intra-ion-pair electron transfer from 9,10-dimethoxyanthracene moiety to iodonium moiety. The counteranion acts as both spectral sensitizer for diphenyliodonium ion and precursor for photo-acid generator.
SYNOPSISAn aqueous-base developable photoresist based on photoinduced cationic polymerization has been prepared by copolymerization of glycidyl methacrylate (GMA) and methacrylic acid (MAA) . The copolymer containing 83 mol % of GMA unit is soluble in an aqueous base and crosslinked in the presence of photogenerated acid caused by acid-initiated ringopening polymerization of pendant epoxide groups. Exposure results in the generation of acid and the subsequent baking process promotes the diffusion of photogenerated acid, which initiates the cationic crosslinking of the epoxide rings. It was also found that the sensitivity of the copolymer was remarkably enhanced when a divinyl ether monomer is added as a bifunctional crosslinker. The sensitivity enhancement may be caused by the high reactivity of the divinyl ether monomer in the presence of acid. The resist comprised of the copolymer, the vinyl ether monomer, and diphenyliodonium 9,lO-dimethoxy-anthracene-2-sulfonate as photoacid generator exhibited the sensitivity of 20 mJ/cm2. A good pattern profile with high resolution was attained by exposure to a 365 nm light followed by a postexposure bake at 6OoC for 3 min.
In a positive photoresist composed of diphenyliodonium 9,10-dimethoxyanthracene-2-sulfonate as a novel photoacid generator, bisphenol A protected with tertbutoxycarbonyl group as a dissolution inhibitor, and a novolak resist matrix, the efficiency of photo-acid generation and deprotective reaction were investigated by means of UV-visible and IR spectroscopies. The quantitative measurement of photogenerated acid by using the acid-sensitive dye exhibited 0.18 as the quantum yield of acid generation in novolak resin film. The lithographic evaluation of this system as a chemically amplified resist was studied. The catalytic chain length for the acidcatalyzed deprotection step was determined as about 100 when 10 min post-exposure bake (PEB) at 80°C was given. The sensitivity and the resolution as a positive resist are 180 mJ/cm2 and higher than 1 p m , respectively under the PEB conditions mentioned above.
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