Work function tuning of metal nitride electrodes for advanced CMOS devices

Abstract

A novel method for tuning the work function of metal nitride (MN x) metal gates by incorporating lanthanide elements into MN x is demonstrated for application in nMOSFETs. The work function (ΦM) of MNx metal gates, such as TaN and HfN, can be tuned continuously down to 4.2-4.3 eV even after rapid thermal annealing (RTA) up to 1000 °C by incorporating lanthanide elements, such as terbium (Tb), erbium (Er), or ytterbium (Yb), into MNx gates. In addition, the lanthanide-MNx metal gates exhibit good thermal stability on both SiO2 and HfAlO high-κ dielectrics in terms of equivalent oxide thickness (EOT) and leakage current, making them promising metal gate candidates in the conventional self-align bulk-Si CMOS process flow. The effect of N in lanthanide-MNx is also studied and the results show that the enhanced nitrogen content in lanthanide-MNx could be of importance for the thermal stability as well as other properties of MNx. © 2005 Elsevier B.V. All rights reserved.