The effect of oxygen in Ru gate electrode on effective work function of Ru/HfO2 stack structure

Effective work function (φ_m,eff) values of Ru gate electrode on SiO₂ and HfO₂ MOS capacitors were carefully examined and discussed from the viewpoint of an effect of oxygen incorporation in Ru gate electrode on φ_m,eff. Annealing at 400 °C in the reduction (3%H₂) and the oxidation (1%O₂) ambient resulted in similar changes in the φ_m,eff of Ru/HfO₂/SiO₂ and Ru/SiO₂ MOS capacitors. Furthermore, the Ru gate MOS capacitor after annealing in the oxidation condition have shown almost the same φ_m,eff value to that of RuO₂ gate MOS capacitors. The oxygen concentration in the Ru/HfO₂ interface after annealing in oxidizing atmosphere is approximately one order of magnitude higher than that after annealing in reducing atmosphere as confirmed by secondary ion mass spectroscopy analysis. Furthermore, the higher oxygen concentration at the Ru/dielectric interface leads to the higher φ_m,eff value, regardless of SiO₂ or HfO₂ dielectrics. This indicates that φ_m,eff of Ru gate MOS capacitor is dominantly determined by the oxygen concentration at the Ru/dielectric layer interface rather than the dipoles originated from the oxygen vacancy in HfO₂.