Role of lanthanum in the gate stack: Co-sputtered TaLaN metal gates on Hf-based dielectrics

Abstract

We examine the characteristics of TaLaN metal gates in direct contact with HfO 2 dielectric, in particular focusing on the effect of La in the gate stack for NMOS applications. Effective work functions (EWF) and vacuum work functions (WF) are measured as a function of lanthanum content in TaLaN without any intentional heating using X-ray photoelectron spectroscopy, U-V photoelectron spectroscopy, and electrical C– V measurements. We find that the addition of lanthanum to tantalum nitride lowered both the EWF and the WF of the metal gate by ∼0.2 eV and ∼0.9 eV, respectively. Furthermore, XPS indicates that lanthanum in TaLaN at the interface with HfO 2 is primarily bonded to nitrogen rather than oxygen and not reacting with the dielectric.