Depth profiles and chemical bonding states of graded doping and ultra-thin HfLaO high-k dielectrics deposited on silicon substrate

La dopant positioning at HfO₂ ultra-thin films was successfully achieved by the co-sputtering method. The depth profiles of graded doping HfLaO (7 nm)/p-Si structures after 850°C RTA were studied. From the nano-AES results, the out-diffusion of Hf atom into Si substrate increases when the La dopant is co-deposited in the upper bond and forming HfLaO/HfO₂/Si structures. On the other hand, the out-diffusion of Hf atoms into Si substrate is suppressed when the La is doped in the lower bond and forming HfO₂/HfLaO/Si structures. It is found that the chance to form silicate becomes insignificant due to less oxygen out-diffusion into Si in the later case. Above is consistent with the binding energies of our XPS results. The electrical properties of different doping locations were measured and compared. The thickness of silicate layer is suggested to be the origin of leakage current.