Multi-Step Flow Synthesis of Photoresist Polymers Involving Copolymerization and Postpolymerization Modifications

We report the synthesis of a model copolymer, poly(4-hydroxystyrene- r -2-methyl-2-adamantyl methacrylate) [poly(HST- r -MAdMA)], suitable for the formulation of chemically amplified photoresists (CARs), using a flow reaction process. The synthesis involves three steps: reversible addition–fragmentation chain transfer (RAFT) copolymerization of 4-acetoxystyrene (ATST) and MAdMA, postpolymerization reactions for RAFT end group removal, and subsequent deacetylation. The flow-based reaction enables the preparation of poly(ATST- r -MAdMA) with precise control over its molecular weight, dispersity, and composition. The subsequent radical reaction for end group removal proceeds rapidly and efficiently, with a reaction time more than four times shorter than that of the corresponding batch process. The flow mode is also effective for the deacetylation step, reducing the reaction time to obtain the final product by approximately a factor of 3. Among these sequential flow reactions, both the RAFT polymerization and postpolymerization end group removal can be performed continuously without precipitation, while maintaining control over structural parameters and achieving end-group-removal efficiencies comparable to those of the separate batch processes. The resulting copolymers can form trench patterns with a critical dimension of approximately 70 nm by electron-beam lithography, achieving a pattern quality comparable to that obtained using copolymers synthesized in the batch mode.