Interface bonding structure of hafnium oxide prepared by direct sputtering of hafnium in oxygen

The interface properties of the hafnium gate oxide films prepared by direct sputtering of hafnium in oxygen with rapid thermal annealing have been investigated in detail. X-ray photoelectron spectroscopy reveals that the interface silicate layer is a random mixture of Hf–O, Si–O, Hf–Si, and excess Hf and Si atoms. The contributions of these bonds to the composition of silicate layer are governed by the Si/Hf ratio. At low Si/Hf ratio (<2), the silicate layer is a mixture of SiO4 and HfO4 phases. At higher Si/Hf ratio (2–5), the contribution of the HfO4 phase decreases and Hf–Si (silicide) bonds become important. At very high Si/Hf ratio (>9) and close to the substrate, Hf–Si dominates and the high strain Hf–Si bonds govern the electrical properties of the interface. These results explain the observed high interface trap density at the HfO2/Si interface and the soft breakdown behavior which is different from the silicon oxide film.