First principles study of Nb–W bilayer metal gate electrode

First principles calculations are performed to study the electronic structure and related properties of the Nb–W interface within NbW multilayer metal gate electrode. It is found that the surface work functions of NbW multilayers are located between those of pure Nb and W surfaces due to the strain effect from the lattice dismatch. The interface energy of Nb(1 1 0)/W(1 1 0) is calculated to be −0.17 J/m2, implying that the Nb–W interface is energetically favorable. Additionally, it is found that the interface dipoles are formed in the interface region to balance the work function difference of W and Nb, and the dipole layers are mainly due to the contributions of interface atoms with a very small contribution from the second atomic layers from the interface. It is of interest to note that the interface W atoms give out a little bit more electrons than the interface Nb atoms during the formation of the interface dipole and that these changes are closely related to the DOS changes.