The influence of lanthanum doping position in ultra-thin HfO2 films for high-k gate dielectrics

Lanthanum dopant positioning at HfO2 ultra-thin films was achieved by the co-sputtering method. The physical properties of graded doping HfO2/HfLaO/p-Si and HfLaO/HfO2/p-Si structures after 850 oC postannealing were compared. The thickness of the monolayer was analyzed by X-ray reflectivity and confirmed by the multiple beam interference model. The HfO2 and silicate phases were characterized by X-ray diffraction patterns. It is found that crystallization depends on the ratio of stacked film thicknesses, and the HfLaO/HfO2/Si structure has more silicate formation at the interface than the HfO2/HfLaO/Si structure. Metal-insulator-semiconductor capacitors were fabricated. The electrical properties including leakage current, conduction mechanism, flatband voltage shift, and barrier height were studied.