Nitroxide mediated polymerization for narrow molecular weight distribution copolymers: application to photoresist materials

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To imprint sub-micron features for microelectronics, photolithography is used to etch the desired pattern with polymers that are sensitive to the irradiation (eg. photoresists). After exposure, patterns are developed by chemical treatment from the photoresists due to solubility changes. Factors such as line width resolution (LWR) that determine feature size depend on the type of polymer used and the properties of the polymer. Typically, conventional free radical polymerization of two or more monomers is used to make the desired copolymer for the photoresist. However, such a polymerization method does not control chain structure well, which is critical for LWR. Controlled radical polymerization (CRP) uses essentially free radical chemistry but can control molecular weight distribution and microstructure very tightly. Some CRP methods (eg. RAFT, ATRP) have been applied for photoresist materials but the major disadvantage is their lack of transparency and they require catalyst and chain transfer agent removal. We aim to apply another variant of CRP termed NMP, which does not leave polymers discoloured but still provides controlled microstructure. NMP has however not been applied towards photoresists. Our project will first evaluate NMP chemistry as a route towards photoresist polymer potentially for 193 nm photoresists with St-Jean Photochemicals Inc. (SJPC) as the industrial sponsor. SJPC will provide their expertise in polymerization chemistry and scale-up facilities for niche materials in the microelectronics industry.