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

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 similar to 0.2 eV and similar to 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. (C) 2008 Elsevier B.V. All rights reserved.