Designing ALD precursors that stay away from the wrong surface

Area-selective ALD depends on a deceptively simple idea: the precursor should react where film growth is wanted, but avoid adsorption on the protected non-growth surface.

For alumina ALD, that balance is difficult. Aluminum precursors are Lewis acidic, and even reversible adsorption on an inhibitor-covered SiO₂ surface can erode selectivity. In a recent publication, Maue and co-workers use pEDA in AMS-BAND to turn that qualitative problem into a quantitative bonding analysis.

The key value of pEDA is that it separates precursor adsorption into chemically meaningful contributions: electrostatics, orbital interactions, Pauli repulsion, dispersion, and surface or precursor deformation. This makes it possible to see why a precursor binds, not only how strongly it binds.

The study shows that Lewis acidity is often a useful guide for adsorption strength, but not the whole story. Bulky branched ligands can weaken surface binding by steric repulsion, while dimerization can reduce adsorption by making surface bond formation less accessible. In the most relevant AS-ALD scenario, adsorption between inhibitor molecules is strongly penalized by Pauli repulsion and deformation of the blocking layer.

The result is a more practical design logic for area-selective deposition: tune precursors not only for reactivity, but for controlled non-reactivity on the protected surface. For physicists, materials scientists, and process engineers working on nanoscale patterning, pEDA offers a way to connect molecular ligand design to selectivity loss mechanisms in real ALD environments.