Structure-Inhibition Relationship of Vapor-Deposited Alkylsilane Monolayers in Area-Selective Atomic Layer Deposition

Area-selective atomic layer deposition (AS-ALD) relies critically on molecular-scale inhibition layers to suppress precursor adsorption in nongrowth regions. Although octadecyltrichlorosilane (ODTS) self-assembled monolayers (SAMs) are widely used, their structural parameters─particularly molecular orientation and grafted molecular areal density─have rarely been systematically correlated with inhibition performance. Moreover, conventional solution-phase deposition introduces contamination risks and extended processing times, limiting practical adoption. Here, we demonstrate a rapid vapor-phase deposition route that forms ODTS blocking layers with improved molecular alignment on SiO2 within 3 min. Angle-dependent near-edge X-ray absorption fine structure (NEXAFS) spectroscopy reveals a reduced molecular tilt angle of ∼29.8 ± 0.3° for vapor-deposited ODTS compared to ∼38.7 ± 0.6° for solution-deposited films, indicating a more upright average molecular orientation and lower orientational disorder. Molecular dynamics simulations establish an inverse correlation between tilt angle and grafted molecular areal density, yielding an estimated density of ∼2 molecules/nm2 for vapor-deposited layers. When applied as ALD inhibitors, the vapor-deposited ODTS layers exhibit improved blocking behavior for HfO2 and Ru ALD compared with the solution-deposited ODTS layers prepared in this study. For HfO2 ALD, image-based analysis at the same projected area fraction shows a ∼35% decrease in nucleation density on D-ODTS, while Ru nucleation is strongly suppressed on D-ODTS, with only isolated nuclei observed within the examined field of view. These results indicate that average molecular orientation and effective grafted molecular areal density are correlated with precursor-accessible nucleation pathways and ALD inhibition efficiency.