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Effects of Si/Ni Composition Ratio of NixSiy Gate Electrode and Hf/Si Composition Ratio of Hf-Based High-k Insulator on Threshold Voltage Controllability and Mobility of Metal–Oxide–Semiconductor Field-Effect Transistors

We have investigated the threshold voltage (VT) controllability of metal–oxide–semiconductor field-effect transistors (MOSFETs) consisting of a Ni or Ni-full-silicide (Ni-FUSI) metal gate and a Hf-based high-k dielectric. We found that the Ni and Hf composition ratios in the metal electrode/HfSiON gate stacks are key factors for controlling the VT and fixed charge in a HfSiON film. Decreasing the Si/Ni ratio of the gate electrode and the Hf/Si ratio of the gate dielectric relieved Fermi level pinning. Increasing the Hf/Si ratio increased the negative fixed charge in the film. In particular for HfO2, only the pure Ni electrode prevended Fermi level pinning. In the case of HfSiON whose Hf/Si ratio was 1.0, NiSi2 and NiSi phases were suitable for nFETs, and the Ni3Si phase and the pure Ni electrodes were suitable for pFETs. It was also found that the electron mobility of Ni-FUSI nFETs depended on the crystalline phase, while no marked degradation of hole mobility was observed in pFETs.