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°CN2 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.

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