Work function tuning of metal nitride electrodes for advanced CMOS devices

A novel method for tuning the work function of metal nitride (MNx) metal gates by incorporating lanthanide elements into MNx 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.