Influence of incorporated non-metallic impurities on electromigration in copper damascene interconnect lines

Low electromigration in Cu interconnect lines represents one of the major challenges for a good performance of semiconductor devices. Referring to this, experiments were carried out to study the influence of non-metallic impurities like Cl, S, and C incorporated in Cu during the electrochemical deposition. In the case of a lower impurity content a higher resistance against electromigration was verified. The electromigration activation energy for metallizations with small contaminations was found to be (1.00 ± 0.06) eV whereas Cu interconnect lines with high non-metallic impurities revealed an activation energy of (0.65 ± 0.03) eV. The electromigration induced degradation by void formation starts at the top interface between Cu and dielectric cap layer. Probably, this results from high mechanical stresses due to differences in material properties or due to an interface weakening by the segregation of S and C impurities.