Influence of Trifunctional RAFT Chain-Transfer-Agent-Mediated Polymerization Conditions on the Negative-Tone Patterning Behavior of Methacrylate-Based Photoresists

Chemically amplified resist performance is governed by the combined effects of polymer structure, molecular characteristics, thermal behavior, and processing conditions. In this study, methacrylate-based photoresist polymers were prepared under different chain-transfer-agent (CTA)-mediated polymerization conditions using a multifunctional three-arm RAFT agent, TMP-CEPA3, while maintaining the same nominal HEMA:TCDMA:MAMA feed composition. HTM CTA 0, HTM CTA 8, and HTM CTA 16 exhibited comparable incorporated monomer compositions, similar weight-average molecular weights, and narrow dispersities, allowing their thermal and lithographic behaviors to be compared without large compositional differences. Thermal analysis showed no monotonic dependence of glass-transition behavior or thermal response on TMP-CEPA3 loading. FT-IR spectroscopy revealed spectral changes after UV exposure and PEB that were consistent with photoacid-mediated chemical changes involving the MAMA-derived acid-labile groups. Negative-tone lithographic evaluation showed a strong dependence on post-exposure baking (PEB) temperature. At 90 °C, all three formulations produced discernible patterns, with HTM CTA 0 and HTM CTA 8 showing slightly clearer pattern definition than HTM CTA 16. Line-pattern evaluation over nominal feature sizes of 10–80 μm likewise showed favorable pattern formation for CTA 0 and CTA 8. Overall, increasing TMP-CEPA3 loading did not systematically improve patterning behavior, indicating that resist behavior is governed by the combined effects of polymerization conditions, polymer characteristics, and lithographic processing parameters.