Ligand-Mediated Nuclearity Tuning of Tin Oxo Clusters for Advanced Lithography

Hybrid tin oxo clusters (SnOCs) have emerged as promising molecular resists for electron-beam (EB) and extreme-ultraviolet (EUV) lithography; however, their patterning mechanisms remain poorly understood due to the coupled effects of ligand electronics, cluster nuclearity, and electron-induced fragmentation. In this study, we demonstrate a ligand-mediated nuclearity tuning strategy that enables the selective synthesis of Sn₆- and Sn₃-based clusters using electron-donating carboxylate and electron-withdrawing diphenylphosphinate ligands, respectively. Density functional theory calculations, electrostatic potential analysis, and bond dissociation energy evaluations show that ligand electronic properties dictate the preferred electron-driven cleavage pathways. Sn₆ clusters predominantly undergo Sn-alkyl bond scission, whereas aromatic phosphinate ligands in Sn₃ clusters stabilize the framework and suppress ligand fragmentation. These trends are supported by XPS and TOF-SIMS analyses, which reveal extensive alkyl cleavage and organic-inorganic crosslinking in Sn₆-based resists, in contrast to minimal ligand decomposition and a robust Sn─O─P network in Sn₃ systems. As a result, Sn₆ clusters exhibit high EB sensitivity (D₀ = 285 µC cm^-2) and sub-30 nm resolution, while Sn₃ clusters deliver ultra-low line-edge roughness (1.02 nm) and excellent pattern fidelity. This work identifies nuclearity as a chemically tunable parameter for rational molecular-resist design.