We report the rational design and synthesis of acid-cleavable 3-arm polymers via core-first approach using a degradable reversible addition–fragmentation chain transfer (RAFT) agent, in which three chain transfer units are attached to the core through acetal bonds that are cleavable under acidic conditions. Its efficacy is confirmed through RAFT polymerization of methyl methacrylate (MMA), resulting in 3-arm PMMA with a molecular weight reduction to ≈30% of its original value after acid treatment. This approach is extended to a 3-arm terpolymer suitable for chemically amplified resists, exhibiting significantly enhanced sensitivity compared to the conventional linear terpolymer: onset energy for development decreases by ≈21% (DUV) and ≈50% (e-beam), while the energy at which development ends decreases by ≈50% for both. With DUV light, pattern formation is achieved at ≈50% lower energy than the linear terpolymer, and with e-beam, sub-100 nm pattern definition is demonstrated, which is not feasible with the linear terpolymer. The enhanced sensitivity and patternability stem from reduced molecular weight and functional group transformation induced by acid released from a photoacid generator. These findings highlight the significance of rationally designing multiarm architectures to tailor the structure and functionality of complex copolymers through an effective synthetic route, offering potential applications in advanced photoimaging materials and broader stimuli-responsive systems.
Lee et al. (Mon,) studied this question.