Study of a new electromigration failure mechanism by novel test structure

A novel electromigration (EM) structure is designed and characterized with advanced Cu/low-k technology. Comparing the EM results derived from novel and traditional test structures, a new EM failure mechanism is proposed. The new mechanism is caused by the Cu/barrier interface damage at the metal line-edge during upper Via opening process. This damage provides a fast diffusion path. From the downstream EM test, it is observed that the thicker Ta-based ALD barrier has a higher activation energy and median time to failure compared to thinner Ta based barrier. Thicker barrier process enhances Cu/barrier adhesion and hence prevent the via opening induced interface damage.