Work function tuning and material characteristics of lanthanide-incorporated metal nitride gate electrodes for NMOS device applications

A versatile method to tune the work function dim of metal nitride (MNx) metal gates by incorporating lanthanide elements for the applications in NMOS devices is demonstrated. By incorporating lanthanide elements such as terbium (Tb), erbium (Er), or ytterbium (Yb) into MNx metal gates such as TaN and HfN, the work function of these MNx can be tuned continuously down to 4.2-4.3 eV even after rapid thermal annealing up to 1000 degrees C, owing to the very low Phi(M) values of lanthanide elements. Material and electrical properties of lanthanide-MNx are investigated, and the results indicate that N concentration is an important parameter for the resistivity, work function, and thermal stability of lanthanide-MNx metal gates. Therefore, it needs to be carefully optimized in the process. In addition, transistor characteristics with Ta0.9Tb0.1Ny on SiO2 are also demonstrated, and several issues regarding the process integration of these novel materials are discussed.