Hydrophilicity-Tuned Iodine-Containing Quasi-Alternating Copolymers for Extreme Ultraviolet Lithography

Extreme ultraviolet lithography (EUVL), employing chemically amplified photoresists (CARs), has emerged as the preferred patterning technique for advanced integrated circuit fabrication. Enhancing photon absorption in CAR films is advantageous for further improving the commercial viability of EUVL; accordingly, incorporating elements with high EUV absorption cross sections into CAR formulations represents a practical strategy, with iodine being a particularly promising candidate. To implement this approach while preserving the chemical uniformity of the CAR polymer matrix, an iodine-containing alternating copolymer, P(IPMi-alt-tBSt), composed of N-(4-iodophenyl)maleimide (IPMi) and tert-butoxystyrene (tBSt), was designed. The target polymer was successfully synthesized with low molecular weight and a narrow molecular-weight distribution; however, its iodine-induced hydrophobicity hindered dissolution in standard aqueous developers, resulting in poor lithographic pattern formation. To address this limitation, the hydrophilic comonomer, N-(4-hydroxyphenyl)maleimide (HPMi), was introduced into the copolymer backbone. The resulting composition-tuned quasi-alternating copolymer, P(IPMi/HPMi-alt-tBSt)-3, exhibited improved dissolution behavior, enabling sub-100 nm positive-tone patterning under focused electron-beam irradiation. Furthermore, its thin films became soluble upon exposure to 11 mJ/cm2 of EUV irradiation. These findings demonstrate that iodine-containing quasi-alternating copolymers, when appropriately tuned for hydrophilicity, represent a promising platform for EUV photoresist development.