Chain-End-Dependent Free Volume, Lithographic Roughness, and Etch Resistance of RAFT-Synthesized Poly(ECPMA-co-HOST) Photoresists

 Advanced semiconductor lithography requires polymer resists with controlled molecular architecture, high etch durability, and low pattern roughness. In this study, low-dispersity poly(ECPMA-co-HOST) copolymers were synthesized by RAFT polymerization as model chemically amplified photoresist platforms. To clarify the role of chain-end chemistry, RAFT-derived thiocarbonylthio groups were systematically converted through multiple post-polymerization routes. Radical-induced end-group modification was examined using hydrogen donors, peroxide initiators, and azo initiators, while aminolysis-mediated thiol formation was used for coupling with pyrene and POSS containing moieties. The resulting polymers were characterized by NMR, FT-IR, XRD, GPC, UV–vis, DSC, and TGA to confirm structural changes and evaluate how terminal functionality affects molecular-weight distribution, optical absorption, and thermal properties. Lithographic patterning and dry-etching tests correlated chain-end structure with line-edge/line-width roughness and etch resistance. Surface roughness, film-thickness profiles, and pattern morphology were further analyzed using AFM, surface profilometry, SEM, and optical microscopy. The chain-end-converted polymers exhibited distinct changes in glass-transition behavior and resist performance, indicating that terminal functionality can influence polymer packing, process stability, and plasma durability even at similar copolymer compositions. This work demonstrates that RAFT polymerization combined with targeted chain-end conversion is an effective strategy for independently controlling molecular uniformity and terminal functionality in photoresist polymers. These results provide insight into how subtle chain-end structures contribute to lithographic roughness and plasma etch performance, offering a molecular design guideline for next-generation semiconductor photoresists.