Copper stress migration

A failure mechanism in semiconductor devices. Due to the combination of different materials and process temperatures used in chip fabrication, the Cu lines in advanced Cu technologies exist in a state of tensile stress. When geometric configurations produce local peaks in stress and when such a peak exists at a location of marginal adhesion or at a pre-existing process-induced void, large stress gradients are created. The term stress migration (stress-induced voiding, or simply stress voiding) refers to the movement of metal atoms under the influence of such a mechanical stress gradient. Little metal movement (migration) occurs until the stress exceeds the yield-point of the metallization. Then atoms diffuse from sites of low stress into regions of high stress and contribute to void growth, and when the void is large enough, the void can cause an electrical open or sufficient resistance increase to interfere with chip functionality. (Reference JEP122F)