Fermi-Level Pinning Induced Thermal Instability in the Effective Work Function of TaN in TaN/SiO 2 Gate Stack

Abstract

In this letter, we demonstrate for the first time that the Fermi-level pinning caused by the formation of Ta(N)-Si bonds at the TaN/SiO 2 interface is responsible for the thermal instability of the effective work function of TaN in TaN/SiO 2 devices after high temperature rapid thermal annealing (RTA). Because of weak charge transfer between Hf and Ta(N) and hence negligible pinning effect at the TaN/HfO 2 interface, the effective work function of TaN is significantly more thermally stable on HfO 2 than on SiO 2 dielectric during RTA. This finding provides a guideline for the work function tuning and the integration of metal gate with high-κ dielectric for advanced CMOS devices.