Evaluation of tantalum silicon alloy systems as gate electrodes

The effect of Si concentration on the effective work function of tantalum silicon (Ta-Si) alloy systems as gate electrodes in direct contact with SiO2 and HfSiOx gate dielectrics has been studied extensively. It was found that the Si concentration in the Ta-Si electrodes (>= 60 at. % Si) has a strong effect on the effective work function, and three discrete composition-dependent phases (tantalum metal, tantalum silicide, and silicon) coexist in the films. The film resistivity and density also change dramatically as a function of Si concentration. Physical analysis shows that these Si-rich Ta-Si electrodes are amorphous at room temperature and crystallize with a 1000 degrees C, 5-s anneal. Finally, an effective work function value of 3.98 eV has been achieved by arsenic implantation of a capacitor electrode layer in Ta-Si/HfSiOx film systems, thereby producing a potential n-type metal gate electrode in conjunction with high-k gate dielectrics. (c) 2005 American Institute of Physics.