Effects of post metallization annealing on modulation in effective work function of platinum gate electrode in germanium metal-oxide-semiconductor devices

The inherent contributions of Fermi level pinning in Ge metal-oxide-semiconductor devices with Pt/HfO₂ gate stacks were investigated by examining the impact of thermal treatment in forming gas (FG) and oxygen environments on the effective metal work function (φ_m,eff) of the Pt gate electrode. The φ_m,eff of the Pt gate electrode for as-deposited devices was extracted to be ∼4.1 eV. However, the FG annealing process led to the increase in the φ_m,eff of the Pt gate electrode up to ∼4.5 eV, whereas no variation was noticed after oxygen annealing process. The interstitial hydrogen atoms with negative charge introduced by the FG annealing compensate positively charged dipoles associated with the Fermi level pinning of Ge. This could be responsible for the increased φ_m,eff of the Pt gate electrode in FG-annealed devices.