Density functional theory study of initial stage of HfO2 atomic layer deposition on hydroxylated SiO2 surface

Density functional theory is employed to investigate atomic layer deposition (ALD) mechanism of HfO2 on hydroxylated SiO2 surface using HfCl4 and H2O as precursors. The ALD process involves two alternate deposition half-reactions: (1) HfCl4 with the SiO2-OH* surface site, and (2) H2O with the SiO2-O-HfCl* surface site. Combined potential energy surface and intrinsic reaction coordinate studies show that both the half-reactions proceed through an analogous trapping-mediated mechanism and a similar transition state. By comparison of the reaction energies of precursors on different size model surfaces, we find that the cluster size has a major effect on the HfCl4 half-reaction, especially on the formation of HfCl4 chemisorbed complex, as compared to the H2O half-reaction. We also find that the intermediate stability is lowered as the surface temperature is raised, which in turn results in desorption increasing of adsorbed precursors.