Precursor Design Principles for Area-Selective Atomic Layer Deposition of Alumina: Quantifying the Role of Lewis...

In atomic layer deposition (ALD), precursor adsorption plays a critical role in determining growth characteristics. This is particularly important in area-selective ALD (AS-ALD), where adsorption on the non-growth surface (NGS) leads to selectivity loss. In this context, both the ability of a precursor to access reactive surface groups on the NGS and the strength of its binding are key parameters governing the selectivity in experiment. Adsorption on the NGS is strongly influenced by the precursor's substituents, which control Lewis acidity, steric demand, and propensity for dimerization. We applied energy decomposition analysis for extended systems (pEDA) to a set of commonly used aluminum precursors to quantitatively assess how these factors affect adsorption energetics on SiO₂ as the NGS, with trimethoxypropylsilane (TMPS) as a small-molecule inhibitor (SMI). Using fluoride ion affinity (FIA) as a metric for Lewis acidity, we find that this largely governs the trends in precursor bonding to both the surface and the SMIs. Notable exceptions are precursors bearing branched alkyl substituents for which steric repulsion dominates over Lewis acidity. Lewis acidity furthermore determines whether adsorption between the SMI layer remains energetically favorable. In this regime, steric effects-Pauli repulsion and deformation of the SMI layer-substantially weaken the adsorption. Dimerization generally reduces adsorption energies. This weakening effect is less pronounced, however, when adsorption takes place within the inhibitor layer. Based on these insights on bonding energetics, we recommend targeted modifications of existing aluminum precursors and propose systematic strategies for precursor design aimed at minimizing interactions with the NGS.