Electron trapping properties at HfO2/SiO2 interface, studied by Kelvin probe force microscopy and theoretical analysis*

Electron trapping properties at the HfO2/SiO2 interface have been measured through Kelvin Probe force microscopy, between room temperature and 90 °C. The electron diffusion in HfO2 shows a multiple-step process. After injection, electrons diffuse quickly toward the HfO2/SiO2 interface and then diffuse laterally near the interface in two sub-steps: The first is a fast diffusion through shallow trap centers and the second is a slow diffusion through deep trap centers. Evolution of contact potential difference profile in the fast lateral diffusion sub-step was simulated by solving a diffusion equation with a term describing the charge loss. In this way, the diffusion coefficient and the average life time at different temperatures were extracted. A value of 0.57 eV was calculated for the activation energy of the shallow trap centers in HfO2.