Effective work function (φm,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 φm,eff. Annealing at 400 °C in the reduction (3%H2) and the oxidation (1%O2) ambient resulted in similar changes in the φm,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 φm,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 φm,eff value, regardless of SiO2 or HfO2 dielectrics. This indicates that φm,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.
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