Copper migration and precipitate dissolution in aluminum/copper lines during electromigration testing

Transmission electron microscopy (TEM) was used to examine in detail how microstructural changes take place in aluminum/copper (Al/Cu) lines adjacent to tungsten contacts. The results indicate that the presence of a single grain boundary can increase the electromigration flux of copper along the line by an order magnitude. In line segments where a bamboo grain occurred, copper diffusion appears to be controlled by diffusion along the Al/oxide interface at the surface of the lines. The results also indicate that, in polycrystalline lines, the rate of copper depletion from the cathode is largely determined by the rate of dissolution of the precipitates.