Physical and electrical properties of Ta–N, Mo–N, and W–N electrodes on $HfO2$ high-$k$ gate dielectric

The influence of various types of metal nitride gate electrodes, i.e., tantalum nitride, molybdenum nitride, and tungsten nitride, on electrical characteristics of metal-oxide-semiconductor capacitors with hafnium oxide as the gate dielectric material has been studied. The result shows that both the physical and electrical properties of the high-$k$ gate stack are influenced by the gate electrode materials and the post-metal-annealing temperature. Both the physical thickness and equivalent oxide thickness of the gate stack increased after the high-temperature $N2$ annealing step. The leakage current density decreased with the increase of the annealing temperature from $600to800°C$⁠. The work functions of these metal nitride electrodes decreased with the annealing temperature due to the variance of microstructure and chemical composition, as indicated by x-ray diffraction and second-ion-mass spectroscopy data. These metal nitride electrodes are suitable for $n$-channel metal-oxide-semiconductor device applications after $800°C$ $N2$ annealing because their work functions are between 4.05 and $4.25eV$⁠. The interface state density and oxide trap density of the high-$k$ gate stack were also reduced by the high-temperature $N2$ annealing step.