Positive Role of Iodine Atoms in Chemically Amplified Photoresists for Extreme Ultraviolet Lithography

In this study, we evaluated the feasibility of incorporating elements with high extreme ultraviolet (EUV) absorption cross sections into chemically amplified photoresist (CAR) formulations to mitigate the sensitivity degradation characteristic of EUV lithography (EUVL), particularly in efforts aimed at reducing photon shot noise. We designed experiments to identify high-absorption elements that enhance the radiolysis of photoacid generators (PAGs) under EUV exposure. Bilayer stacks comprising a fluoroalkylated polymer overcoat doped with candidate elements atop an acid-labile polymer underlayer were exposed to EUV radiation, post-exposure baked, and developed. Varying the overcoat composition revealed that iodine (I) increased the underlayer’s solubility, whereas tin (Sn) produced no comparable effect. Guided by this result, we synthesized an iodine-containing radiosensitizer, IOH-A, by introducing acid-cleavable acetal groups into iohexol, a radiocontrast agent used in computed tomography angiography. Incorporating IOH-A into CAR formulations, followed by compositional optimization, yielded a 2.6% improvement in sensitivity and a 12% reduction in line-edge roughness (LER) during EUVL patterning. These results demonstrate a practical strategy to relax the long-standing sensitivity-LER trade-off in EUVL using CARs and propose IOH-A as a promising design motif for next-generation CAR systems.