Effects of surface alloying and orientation on work function of MoTa metal gate

Work functions of sub- and monolayers Mo on metal Ta of various orientations are investigated using first-principles methods based on density functional theory. The calculated results reveal that the work function has strongly orientation dependence. However, for a given surface orientation, the work function is insensitive to distributions of Ta/Mo atoms in the surface layer. Moreover, it is found that work functions of the (100) and (111) surfaces increase with increasing Mo composition in the surface layer but those of the (110) decrease. By analysis of surface dipole density, it is found that the metal work function is mainly determined by surface orientation and surface charge redistribution. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3204976]