Electromigration in epitaxial copper lines on epitaxial underlayers.

摘要

This thesis describes investigation on electromigration (EM) behavior of epitaxial Cu interconnects on epitaxial underlayers.; The results indicate that nitrides underlayers increase the EM resilience of Cu lines by up to a factor of six. Empirical activation energies ( Q) for EM are 0.77 +/- 0.03, 0.76 +/- 0.03, 0.51 +/- 0.04 and 0.55 +/- 0.05 eV for Cu(001)/TiN, Cu(001)/TaN, Cu(001)/Ta and Cu(001)/MgO, respectively. These results correlate well with the adhesion energy (gamma) of Cu with the underlayers.; Dislocation pipe diffusion is not the dominant mechanism of EM. Instead, we find two different mechanisms, related to the gamma of the Cu with the underlayer. For Cu(001) on nitride underlayers, the gamma of Cu-underlayer is higher than that of Cu-Cu oxide film that is present on the Cu surfaces which results in EM occurring predominantly through surface diffusion. This is supported by agreement between the measured Q for EM in Cu with nitride underlayers, and that calculated from the gamma between Cu-Cu oxide. In contrast, the gamma of Cu(001) between Ta and MgO are lower than that of the Cu-Cu oxide, due to which the Cu/Ta and Cu/MgO interfaces serve as the EM pathways.; The shape and location of voids that cause EM-induced line-breakage were directly related to the atom transport pathway. For interfacial diffusion, the voids nucleate at the interface and grow into the film, giving them an upward concave shape. For surface diffusion, the voids nucleate at the top and grow inward into the film, giving them a downward concave shape.; Epitaxial Cu(111) lines exhibit higher EM resistance than Cu(001) lines, probably because the higher symmetry of diffusion anisotropy in (111) plane. Also, from the failure sites of (111) oriented lines we found faceted voids of 6-fold symmetry, most likely due to the high surface diffusion anisotropy in Cu.