Electromigration in sputtered copper films on polyimide

Abstract

Electromigration damage (EMD) is one of the major causes for the failures of interconnects. In this study, the electromigration of Cu on polyimide is investigated. An empirical formula is used to evaluate the EMD of Cu film. The activation energy (Q) obtained is significantly less than those of lattice and grain boundary diffusion. This suggests that the electromigration in copper proceeds via an interfacial diffusion path. The geometry of the metallization also affects the activation energy. Any abrupt change in the interconnect direction and metal width causes current crowding and should be avoided. The current exponents (n), calculated from EMD data, are 3.58 and 3.35 for straight and zig-zag Cu films, respectively.