Investigation of Mg Diffusion in Ta(N) Based Electrodes on HfO2for Sub-32nm CMOS Gate-Last Transistors

Magnesium alloyed with Ta and TaN is investigated as possible gate electrode on HfO2 dielectric. When Mg is deposited on Ta, we observe TaMg alloy formation and HfO2 degradation induced by Mg annealed at 440{degree sign}C. When TaN is deposited on HfO2 prior to Mg, TaN acts as chemical barrier against Mg diffusion and minimizes direct reaction of Mg with HfO2. TaN controls the Mg diffusion through complex mechanisms. Beside, sub-stoichiometric TaNx electrode without any additive is stable on HfO2 at 440{degree sign}C, with N+ 4.3eV band-edge work-function. We discuss on the relevance to use low-work-function additive in refractory metal gate on HfO2 dielectric.