Alkoxy chain-length engineering in heterometallic In–Sn-oxo clusters for nanolithography

Abstract

The limited solubility and solution processability of metal-oxo clusters often hinder their practical applications. To address this, we employed a ligand engineering strategy to synthesize a family of In₄Sn₄-oxo clusters (InOC-31 to InOC-37) sharing an identical core but functionalized with alkoxy ligands of progressively increasing chain lengths (C₁–C₇). The influence of alkoxy chain length and conformation on solubility, solution processability, patterning mechanism, and lithographic performance is thoroughly investigated. Solubility in 4-heptanone increases monotonically from 14.7 mg/mL (C1, InOC-31) to 31.4 mg/mL (C7, InOC-37). The resulting clusters exhibit excellent stability and tunable solubility, enabling high-quality thin-film fabrication via spin-coating. Four representative clusters (InOC-31 to InOC-34) each achieved fine patterning at 50 nm linewidth, with the propoxy-functionalized InOC-33 exhibiting optimal performance, including high sensitivity and better line edge roughness. Combined experimental and theoretical analyses reveal that the exposure mechanism involves Sn–butylene/phenyl–Sn crosslinking, multipath cleavage of carboxylate ligands, and competing decomposition routes of the alkoxy ligands. Notably, we propose a novel mechanism wherein alkoxy chain length dictates the decomposition route proceeding either via direct dissociation or through β-H elimination to form alkenes which critically governs the observed variations in lithographic performance. This newly elucidated lithographic mechanism provides valuable insights for the design of next-generation metal-based photoresist materials.