Work Function Tuning and Material Characteristics of Lanthanide-Incorporated Metal Nitride Gate Electrodes for NMOS Device Applications

摘要

A versatile method to tune the work function φ{sub}M of metal nitride (MN{sub}x) 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 MN{sub}x metal gates such as TaN and HfN, the work function of these MN{sub}x can be tuned continuously down to 4.2-4.3 eV even after rapid thermal annealing up to 1000℃, owing to the very low φ{sub}M values of lanthanide elements. Material and electrical properties of lanthanide-MN{sub}x are investigated, and the results indicate that N concentration is an important parameter for the resistivity, work function, and thermal stability of lanthanide-MN{sub}x metal gates. Therefore, it needs to be carefully optimized in the process. In addition, transistor characteristics with Ta{sub}0.9Tb{sub}0.1N{sub}y on SiO{sub}2 are also demonstrated, and several issues regarding the process integration of these novel materials are discussed.