The metallurgical control of electromigration failure in narrow conducting lines

Electromigration is a serious potential source of failure in the narrow, thin-film Al-Cu conductors used in modern microelectronic devices. The problem has become more acute as line widths have shrunk to below one micrometer, creating lines with quasi-bamboo microstructures. The usual mechanism of internal electromigration failure in such lines involves the formation of a transgranular void across a bamboo grain at the upstream end of a long, polygranular segment, preceded by the depletion of copper from both the polygranular segment and the upstream bamboo grain. At least three metallurgical mechanisms are available to inhibit this failure mechanism and improve the useful lifetime of the line, Each of these methods has been demonstrated in the laboratory environment.