Enhancing 365 nm Photoresist Performance Using 2-Isopropylthioxanthone as a Photosensitizer

Chemical amplification resists (CARs) are critical for advanced lithography, yet nonionic photoacid generators (PAGs) often suffer from low sensitivity. This study investigates the use of 2-isopropylthioxanthone (2-ITX) as a photosensitizer to enhance the performance of i-line (365 nm) photoresist systems. Four PAGs were synthesized, including TFPSO, BrTFPSO, TFPVSO, and BrTFPVSO. TFPSO, BrTFPSO was mixed with copolymers of 2-Ethyl-2-adamantyl methacrylate (EAMA) and 2-Oxotetrahydrofuran-3-yl methacrylate (GBLMA) to obtain a PAG-blended photoresist system. TFPVSO, BrTFPVSO was copolymerized with EAMA and GBLMA to obtain the PAG-bound photoresist system. Photoresist formulations with 10-20 wt % 2-ITX were evaluated for sensitivity, contrast, and acid diffusion. The PAG-blended system with 10 wt % 2-ITX achieved a dose-to-clear (E₀) of 38.4 mJ/cm² with high contrast (γ = 18.5). Elevated postexposure bake (PEB) temperatures (110 °C) further improved sensitivity (E₀ = 5.6 mJ/cm²). PAG-bound systems exhibited reduced acid diffusion (pattern error <1%) but lower sensitivity (E₀ = 150.9-673.7 mJ/cm²). Characterization via ultraviolet-visible (UV-vis) and ¹H NMR spectroscopy revealed that 2-ITX facilitates the transfer of energy to PAGs without participating in the photolytic decomposition process. These findings highlight the crucial importance of 2-ITX in enhancing photoresist performance and show that the inclusion of photosensitizers expands the applicability of photoresists.