Backbone-Length-Optimized Inhibitors Deliver Long-Retention Selectivity in Area-Selective ALD of VO₂

Area-selective atomic-layer deposition (AS-ALD) relies on surface inhibitors; however, their molecular design remains empirical owing to the lack of a unified framework linking the molecular structure to inhibition performance. In this study, we systematically investigate the influence of the carbon-backbone length of trimethoxyphenyl(alkyl)silane small-molecule inhibitors (SMIs) on adsorption behavior and selectivity in the AS-ALD of VO₂. We use density functional theory to show that SMI adsorption on hydroxylated SiO₂ proceeds through a multistep pathway involving physisorption and single- and double-bonded chemisorption. Longer backbones enhance physisorption via stronger dispersion interactions; however, they impose rapidly increasing kinetic barriers to form a stable double-bonded configuration owing to severe steric and conformational constraints. Random sequential adsorption simulations show that the achievable surface coverage is dictated by a tradeoff between the molecular packing density and steric exclusion, resulting in a nonmonotonic dependence on the backbone length. These coupled chemical and geometric effects define the optimal intermediate backbone-length range. This prediction is validated by VO₂ AS-ALD experiments, in which only intermediate-length SMIs maintain high selectivity (> 90%) over extended cycling. This study establishes a predictive and chemically and geometrically grounded design principle for molecular inhibitors in AS-ALD, and broadly for area-selective atomic-layer processing.