Roughness at ZrO2/Si interfaces induced by accelerated oxidation due to the metal oxide overlayer

We investigated reactions at ZrO2/Si interfaces by means of interface oxidation and atomic-scale roughness caused by postoxidation annealing. When fabricating ZrO2 by in situ reoxidation of a thin Zr metal layer, the interface oxidation that results in Zr–silicate formation accelerates, when the initial Zr layer becomes thicker. This implies that interface oxidation is not dominated by oxidant diffusion through the high-k film, but is accelerated by catalytic effects that occurs within the metal oxide. We also found that, in contrast with a SiO2/Si interface, roughness at the high-k/Si interface monotonously increases with the growth of the interface silicate layers. These results demonstrate the importance of postannealing conditions on high-k gate dielectrics.