Self-aligned Copper Oxide Passivation Layer – A Study on the Reliability Effect

The reliability of the plasma etched copper lines with the self-aligned copper oxide passivation layer has been studied with the electromigration stress method. The oxide passivation layer was prepared by plasma oxidation, which covers the entire exposed copper line to prevent the surface oxidation under the ambient condition. The void formation and growth process reflect the line broken mechanism. Voids formed from grain boundary depletion and grain thinning were monitored by optical microscopes. The line failure times with respect to line width and current density were measured. The addition of the oxide passivation layer shortened the lifetime due to the poor heat transfer and copper diffusion, which accelerated the formation and growth of the voids. The narrow line has a longer lifetime than the wide line because of the fewer grain boundaries for flux divergence to form voids. The copper oxide passivation layer was formed self-aligned to the copper line. It also gettered copper atoms diffused from the bulk copper film.