Plasma-assisted As implants for effective work function modulation of TiN/HfO2 gate stacks on germanium

Abstract

The plasma assisted As doping (PLAD) technique is used to demonstrate multiple flatband voltages (multi-Vfb) on TiN/HfO2 Ge gate stacks for n-FinFET applications. Through detailed studies with varying doses, implant energies, and TiN cap thicknesses, we show that the PLAD As technique can be used to obtain effective work function (EWF) modulation from the near midgap to the conduction band edge (up to 280 meV) of Ge, a key technological requirement for multi-threshold voltage (VT) Ge n-FinFETs. Furthermore, there is no deterioration of key gate stack parameters such as gate leakage, effective oxide thickness, and gate/channel interface trap densities. From secondary ion mass spectroscopy data, we attribute the tuning of EWF to As accumulation and interfacial dipole formation at the TiN/HfO2 interface. The experimental observations are reinforced by ab initio simulations of near-interface As substitutions at the TiN/HfO2 interface. As substitution at N sites near the interface reduces the EWF, making it more suitable for n-MOS applications.