Characterization of the electronic structure and thermal stability of HfO2/SiO2/Si gate dielectric stack

X-ray photoelectron spectroscopy was used to investigate thermal stability of HfO2 on SiO2/Si substrate prepared by atomic layer deposition, followed by annealing at different temperature. Hf silicate and Hf silicide are formed at the interface of HfO2 and SiO2 during deposition. The Hf silicide disappears, while the amount of the Hf silicate is intensified after post-deposition annealing treatment at 400 degrees C. Phase separation of the Hf silicate layer occurs when the annealing temperature is over 400 degrees C, resulting in the Hf silicate decomposition into Si and Hf oxides. Moreover, crystallization at high temperature leads to grain boundaries formation, which deteriorates the gate leakage current, as observed by the electrical measurements. The similar annealing temperature dependence of both internal electric field and the amount of Hf silicate implies that the Hf silicate plays a key role in building up the internal electric field, which is attributed to generation of oxygen vacancies (V-o) in the Hf silicate layer. Copyright (c) 2017 John Wiley & Sons, Ltd.