Zirconium and hafnium oxide interface with silicon: Computational study of stress and strain effects

Computations of the periodic double-interface MO₂/Si (M = Zr and Hf) systems using density functional theory (DFT) demonstrate that very thin epitaxial MO₂ layers at silicon (1 0 0) surface adopt anatase-like structure with six-coordinate M atoms, while tetragonal-like MO₂ structure with seven-coordinated M atoms has a lower stability (metastable). This results from a closer match between Si(1 0 0) surface unit cell and anatase-like ZrO₂ and HfO₂ leading to the overall stress reduction if MO₂ adopts the anatase-like structure on silicon. In agreement with the previous study of Gavartin et al. [Gavartin, Fonseca, Bersuker, Shluger, Microelectron. Eng. 80 (2005) 412–415] formation of oxygen vacancy at the interface is demonstrated to be lower than in bulk film. This result appears to be independent from the film or interface structure but originates from the energy balance between M–O, M–M, Si–O and M–Si bonds, as revealed by a simple molecular model.