Influence of copper purity on microstructure and electromigration

Electromigration in copper damascene interconnects is usually associated with interfacial diffusion at the copper/ dielectric barrier interface. In this study, we demonstrate how impurity and microstructural properties of the bulk copper can influence failures at the copper/dielectric barrier interface. Impurity concentrations in the bulk copper were modulated by varying electroplating conditions and the resulting effects on the copper microstructure and electromigration performances were investigated. A higher impurity concentration in the copper was found to increase the formation of microvoids during anneal and reduced the anneal rate which retarded the formation of large grains in the plated films. Both of these effects result in reduced electromigration lifetime with higher impurity level.