Interfacial stability of electroplated Cu on a 5nm Ru film supported by Si, Cu/(5nmRu)/Si, was investigated using Rutherford backscattering and high-resolution analytical electron microscopy. Transmission electron microscopic imaging showed that a 5nm Ru film was amorphous in contrast to the columnar microstructures of thicker films (20nm). Direct Cu plating on a 5nm Ru film yielded a homogeneous Cu film with over 90% plating efficiency. It was demonstrated that 5nm Ru could function as a directly plateable Cu diffusion barrier up to at least 300C vacuum annealing. Transmission electron microscopy revealed an interlayer between Ru/Si, which expands at the expense of Ru upon annealing. Electron energy loss spectroscopy analyses showed no O across the Cu/(5nmRu)/Si interfaces, thereby indicating that the interlayer was RuxSiy. The silicidation was attributed to failure of the ultra-thin Ru barrier at the higher annealing temperature.

5nm Ruthenium Thin Film as a Directly Plateable Copper Diffusion Barrier. T.N.Arunagiri, Y.Zhang, O.Chyan, M.El-Bouanani, M.J.Kim, K.H.Chen, C.T.Wu, L.C.Chen: Applied Physics Letters, 2005, 86[8], 083104 (3pp)