5 nm ruthenium thin film as a directly plateable copper diffusion barrier

Interfacial stability of electroplated copper on a 5 nm ruthenium film supported by silicon, Cu/(5 nm Ru)/Si, was investigated using Rutherford backscattering and high-resolution analytical electron microscopy. Transmission electron microscopy (TEM) imaging shows that a 5 nm Ru film is amorphous in contrast to the columnar microstructures of thicker films (20 nm). Direct Cu plating on a 5 nm Ru film yielded a homogeneous Cu film with over 90% plating efficiency. It is demonstrated that 5 nm Ru can function as a directly plateable Cu diffusion barrier up to at least 300 degrees C vacuum anneal. TEM reveals an interlayer between Ru/Si, which expands at the expense of Ru upon annealing. Electron energy loss spectroscopy analyses show no oxygen (O) across the Cu/(5 nm Ru)/Si interfaces, thereby indicating that the interlayer is ruthenium silicide (RuxSiy). This silicidation is mainly attributed to the failure of the ultrathin Ru barrier at the higher annealing temperature. (c) 2005 American Institute of Physics.