Plasma-Assisted Low Energy N-2 Implant For V-Fb Tuning Of Ge Gate Stacks

This work reports V-fb tuning of TiN/HfO2 gate stacks on Ge using low energy plasma-assisted doping with N-2 without significant impact on gate capacitance and gate/channel interface trap densities. As required for multi-V-T Ge p-FinFETs, controlled change in effective work function up to 180mV from the near midgap to the near valence band edge of Ge is demonstrated by varying implant dose and energy. Unlike Si gate stacks, increased gate leakage in implanted Ge gate stacks is shown to result from traps created in the HfO2 layer during the implant and exposed to channel carriers due to a low band offset GeO2 interfacial layer (IL). Recovery of gate leakage is demonstrated by substituting GeO2 with an Al2O3 IL. Further, a simple physical model is proposed to extract the work function and oxide charge components of the change in V-fb for varying implant doses and energies. Published by AIP Publishing.