Effect of the crystallinity on the long-term reliability of electroplated copper thin-film interconnections

In this study, the crystallinity of electroplated copper thin-film interconnections on Cu and Ru seed layers before and after EM (Electro migration) test was evaluated by an EBSD (Electron Back-scattered Diffraction). The EM resistance of the interconnection on the Ru seed layer was improved drastically compared with that on the Cu one. EBSD analyses revealed that the crystallinity of the interconnection on the Ru seed layer was much higher than that on the Cu one. In particular, the density of random grain boundaries with low crystallinity decreased in the interconnection on the Ru seed layer. It was concluded, therefore, that the improvement of the crystallinity of the electroplated copper thin-film interconnection by using the seed layer that can reduce the lattice mismatch between Cu and a barrier layer material is effective for assuring the high EM resistance and thus, the long-term reliability of the interconnection.