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 N-2 annealing step. The leakage current density decreased with the increase of the annealing temperature from 600 to 800 degrees 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 degrees C N-2 annealing because their work functions are between 4.05 and 4.25 eV. The interface state density and oxide trap density of the high-k gate stack were also reduced by the high-temperature N-2 annealing step. (c) 2006 American Vacuum Society.