Reliability Characteristics of La-doped High-k/Metal Gate nMOSFETs

The reliability of hafnium oxide gate dielectrics incorporating lanthanum (La) is investigated. nMOSFETs with metal/La-doped high-k dielectric stack show lower VSUBth/SUB and ISUBgate/SUB, which is attributed to the dipole formation at the high-k/SiO₂ interface. The reliability results well correlate with the dipole model. Due to lower trapping efficiency, the La-doping of the high-k gate stacks can provide better PBTI immunity, as well as lower charge trapping compared to the control HfSiO stacks. While the devices with La show better immunity to positive bias temperature instability (PBTI) under normal operating conditions, the threshold voltage shift (ΔVSUBth/SUB) at high field PBTI is significant. The results of a transconductance shift (ΔGSUBm/SUB) that traps are easily generated during high field stress because the La weakens atomic bonding in the interface layer.