Electromigration-induced Plasticity and Texture in Cu Interconnects

Abstract

Plastic deformation has been observed in damascene Cu interconnect test structures during an in‐situ electromigration experiment and before the onset of visible microstructural damage (ie. voiding) using a synchrotron technique of white beam X‐ray microdiffraction. We show here that the extent of this electromigration‐induced plasticity is dependent on the texture of the Cu grains in the line. In lines with strong 〈111〉 textures, the extent of plastic deformation is found to be relatively large compared to our plasticity results in the previous study[1] using another set of Cu lines with weaker textures. This is consistent with our earlier observation that the occurrence of plastic deformation in a given grain can be strongly correlated with the availability of a 〈112〉 direction of the crystal in the proximity of the direction of the electron flow in the line (within an angle of 10°). In 〈111〉 out‐of‐plane oriented grains in a damascene interconnect scheme, the crystal plane facing the sidewall tends to be a {110} plane,[2–4] so as to minimize interfacial energy. Therefore, it is deterministic rather than probabilistic that the 〈111〉 grains will have a 〈112〉 direction nearly parallel to the direction of electron flow. Thus, strong 〈111〉 textures lead to more plasticity, as we observe.