(Invited) Mechanism of Vfb Shift in HfO2 Gate Stack by Al Diffusion from (TaC)1-xAlx Gate Electrode

We investigate Vfb behavior of (TaC)1-xAlx gated HfO2 MOS capacitors as a function of post metal annealing (PMA) temperature. The positive Vfb shift appears in PMA temperature at above 700 °C, while the negative Vfb shift occurs at below 600 °C. At below 600 °C, the effective work function (φm,eff) of gate electrode becomes lower by increasing Al atoms with a low work function. We found that the positive Vfb shift occurs dominantly due to the φm,eff change induced by Al diffusion from gate electrode at 700 and 800 °C. At above 900 °C, Al atoms reach to the HfO2/SiO2 interface and form the AlOx layers, and results in positive Vfb shift due to the bottom interface dipole. We can divide into two components of φm,eff change of gate electrode and the bottom interface dipole due to AlOx layer as a function of PMA temperature.