Theoretical Investigation on Lithographic Properties of Zinc–Oxo and Cadmium–Oxo Clusters Ligated with Differently Substituted Benzoic Acids

Zinc-oxo clusters offer advantages over polymer resists for extreme ultraviolet lithography (EUVL) due to their smaller size and higher EUV absorptivity. Although cadmium-oxo clusters provide higher EUV absorption, their severe toxicity necessitates safer alternatives. Elucidating the differences between zinc-oxo and cadmium-oxo clusters is key to identifying the origin of high performance in metal-oxo clusters (MOCs) and guiding the design of safer materials. This study employs density functional theory (DFT) to investigate the lithographic properties of ten distinct zinc-oxo and cadmium-oxo clusters (M-L) ligated with benzoic acid (BA), 4-methylbenzoic acid (MBA), 4-vinylbenzoic acid (VBA), 4-trifluoromethylbenzoic acid (TBA), and 4-cyanobenzoic acid (CBA). Results demonstrate that the VBA and CBA enable zinc-oxo clusters to surpass cadmium-oxo counterparts in lithographic properties. Analysis of the state with the highest oscillator strength reveals Zn-L, Cd-CBA, and Cd-VBA cluster transitions are dominated by local excitation (LE), whereas Cd-BA, Cd-MBA, and Cd-TBA clusters form hybrid LE/charge transfer (CT) states with metal participation. Thermodynamic and kinetic calculations confirm all clusters undergo photoreactions through three pathways (ionization, electron attachment, and radical process), demonstrating a synergistic Coulomb-induced and radical-mediated mechanism. This study establishes quantitative structure-property relationships for the design of high-performance and environmentally safer MOC photoresists.