Accurately computed dimerization fraction of ALD precursors and their impact on surface reactivity in area-selective atomic layer deposition

The Lewis acidic nature of aluminum atoms in common precursors for the atomic layer deposition (ALD) of Al2O3 can lead to dimerization. This study investigates whether these compounds predominantly exist as monomers or dimers under ALD conditions. Understanding dimerization is crucial for discussing precursor reactivities and other properties, especially in the context of area-selective ALD (AS-ALD). We employed a theoretical approach, incorporating conformer search, density functional theory, and coupled cluster calculations, to determine the dissociated dimer fraction for a range of precursors under typical ALD pressures and temperatures. The precursors studied include aluminum alkyls, chlorinated aluminum alkyls, dimethylaluminumisopropoxide (DMAI), and trisdimethylamidoaluminum (TDMAA). Our findings indicate that aluminum alkyls are completely dissociated over the whole parameter range, while DMAI and TDMAA form stable dimers. Chlorinated precursors were found to exist in both monomeric and dimeric forms depending on temperature and pressure.