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 PhiMof 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 MNxmetal gates such as TaN and HfN, the work function of these MNxcan be tuned continuously down to 4.2-4.3 eV even after rapid thermal annealing up to 1000 degC, owing to the very low PhiMvalues of lanthanide elements. Material and electrical properties of lanthanide-MNxare investigated, and the results indicate that N concentration is an important parameter for the resistivity, work function, and thermal stability of lanthanide-MNxmetal gates. Therefore, it needs to be carefully optimized in the process. In addition, transistor characteristics with Ta0.9Tb0.1Nyon SiO2are also demonstrated, and several issues regarding the process integration of these novel materials are discussed