We investigated flatband voltage (Vfb) behavior for several Hf-based high-k dielectrics, including HfO2, Mg-, and La-incorporated HfO2, HfSiOx, and Mg-, La-, and N-incorporated HfSiOx, during the reduction (forming gas annealing: FGA) and oxidation annealing (ODA) processes. A negative Vfb shift appeared in all high-k dielectrics as the FGA temperature increased. In contrast, a positive Vfb shift was observed after the introduction of additional oxygen into the high-k layer during ODA. The oxygen diffusion coefficient (D) values of all samples were estimated using Fick's law. The results showed that the D value of the HfO2 dielectric was five times as large as that of the HfSiOx dielectric in ODA at 400 degrees C. Furthermore, the Mg-, La-, and N- incorporated high-k dielectrics exhibited a larger D value compared with the pure high-k dielectrics. These results strongly suggest that the ionicity of high-k dielectrics, which we attribute to a large positive Vfb shift, enhances oxygen diffusion in the high-k layer. (c) 2011 Elsevier B.V. All rights reserved.