Suitable passivation thickness on a metal line to prevent electromigration damage

Electromigration (EM) is a serious problem for an Al line subjected to high-density electron flow. The present work reports a strategy for achieving a suitable passivation thickness on the line against EM damage. Experiments carried out in this work indicated that the threshold current density, a measure of EM resistance, increased with increasing passivation thickness and became saturated for thicknesses greater than 1700 nm. The saturation was shown to begin at the situation in which the level of the passivation top surface beside the Al line and that of the Al top surface are the same. A suitable passivation thickness for effectively increasing EM resistance was determined based on this finding.