Effect of Acid-Labile Protecting-Group Structure on the Micrometer-Scale Patterning Performance of Core-First RAFT-Synthesized Three-Arm Photoresists.

Controlling dimensional fidelity and line-edge roughness is important in chemically amplified negative-tone imaging. In this study, two three-arm random terpolymers containing different acid-labile protecting groups were synthesized via core-first reversible addition-fragmentation chain-transfer (RAFT) polymerization to examine the influence of protecting-group structure within a common star-polymer framework. HTT 334 contained tert-butyl methacrylate (t-BMA), whereas HTM 334 contained 2-methyl-2-adamantyl methacrylate (MAMA). The two polymers exhibited comparable molecular weights and compositions, with narrow dispersities of 1.14 and 1.16. Thermal analysis showed that HTM 334 had a slightly higher glass-transition temperature than HTT 334 (77 and 73 °C, respectively). Fourier transform infrared (FT-IR) spectroscopy revealed spectral changes after exposure and post-exposure baking (PEB) that were consistent with acid-catalyzed deprotection and possible intermolecular reactions involving the hydroxyethyl methacrylate units. Negative-tone patterns were formed using an n-butyl acetate developer under the selected PEB conditions of 70 °C for HTT 334 and 90 °C for HTM 334. Across nominal mask dimensions of 10-80 μm, HTM 334 exhibited printed-to-mask critical-dimension ratios of 0.990-1.039, compared with 0.915-1.003 for HTT 334. HTM 334 also showed lower measured line-edge roughness values of 0.22-0.39 μm than HTT 334, which showed values of 0.52-1.27 μm. At the nominal 10 μm dimension, HTM 334 exhibited a line-edge roughness of 0.27 μm and an LER/CD ratio of 2.60%. These results indicate that an acid-labile protecting-group structure can influence thermal behavior and micrometer-scale pattern fidelity within the investigated three-arm RAFT polymer platform.