Insights into the Surface Chemistry of Tin Oxide Atomic Layer Deposition from Quantum Chemical Calculations

The surface chemistry and growth characteristics of tin oxide atomic layer deposition (ALD) from tetrakis(dimethylamino)tin (TDMASn) and H2O have been investigated by density functional theory and second-order Møller–Plesset perturbation theory calculations. The determined reaction pathways provide the basis for a mechanistic understanding of SnOx ALD on OH-terminated silicon and facilitate analysis of previous experimental observations. In particular, the calculations provide insight into the origin of the experimentally observed increase in the growth rate of SnOx at temperatures below 100 °C, for which the role of physisorbed H2O has been suggested, by demonstrating that the energetics for the TDMASn reaction with surface OH groups are similar to that with H2O molecules. Also, the reaction barrier for the water half reaction is shown to depend on the presence of hydroxyl groups adjacent to O2SnN(CH3)2* reaction sites on the growth surface, and this plays a role in the SnOx ALD at low deposition temperatures. The surface chemistry understanding developed here for SnOx is expected to be of relevance for the ALD of other technologically promising materials such as zinc tin oxide.