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 Phi
_M
of metal nitride (MN
_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
_x
metal gates such as TaN and HfN, the work function of these MN
_x
can be tuned continuously down to 4.2-4.3 eV even after rapid thermal annealing up to 1000 degC, owing to the very low Phi
_M
values of lanthanide elements. Material and electrical properties of lanthanide-MN
_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
_x
metal gates. Therefore, it needs to be carefully optimized in the process. In addition, transistor characteristics with Ta
_0.9
Tb
_0.1
N
_y
on SiO
₂
are also demonstrated, and several issues regarding the process integration of these novel materials are discussed