The continuing drive towards deep sub-micron silicon technology has been stimulated by the demand for higher operating frequencies, greater circuit complexity and lower power consumption. At high current densities there is significant transfer of momentum to the metal ions from the electrons which compose the electric current.
Metal ions diffuse along grain boundaries, along the track surface or through the metal grains.
The shrinking lateral dimensions of all integrated circuit components means that less ion diffusion is necessary before line failure occurs. Thus there are many important reliability issues specific to Cu-based metallisation. There is a clear, urgent, need for research on Cu metallisations which will become dominant for many devices. While full process integration for Cu has been achieved there is little published information on the detailed microscopic mechanisms of failure which thus need academic input. It seems likely that Al will continue to be used for many technologies, perhaps with damascene Al serving as a stepping stone with Cu being used to for the most advanced technologies.