Effective control of flat-band voltage in HfO2 gate dielectric with La2O3 incorporation

The origin of negative flat-band shift using La₂O₃ incorporation in HfO₂ dielectrics has been extensively examined. From careful extraction of effective work function of gate electrode and fixed charges at each interface, it has been revealed that La₂O₃ at high-k/Si substrate or high-k/SiO₂ interface has either large amount of positive fixed charges or an additional dipole of 0.36 V compared to that of HfO₂/Si or HfO₂/SiO₂. Stacked MOSCAPs were fabricated and the C-V characteristics show that flat-band voltage shift is mainly determined by high-k film which is in contact to Si or SiO₂. Using HfLaO with different La concentration, the amount of shift in flat-band voltage could be well controlled, which might be due to the diffusion or pile-up of La atoms to the interface over 420degC. This study provides further insights in controlling the threshold voltage of HfO₂ based oxides.