Evaluation of tantalum silicon alloy systems as gate electrodes

Abstract

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 (⩾60at.% 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°C, 5-s anneal. Finally, an effective work function value of 3.98eV 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.