Diffusion and electromigration of copper in SiO2-passivated single-crystal aluminum interconnects

We have experimentally studied the diffusion and electromigration of Cu in passivated single-crystal Al interconnects, fabricated on oxidized Si wafers. The test structure consisted of parallel lines (0.4 mu m thick and 5 mu m wide), with alternating lines terminating in shared contact pads. Cu was locally added to the same regions in all the lines, and the effects of temperature and electric fields on diffusion along the lines were characterized by analyzing the Cu concentration profile measured by electron-probe microanalysis. The activation energy for diffusion was found to be 0.8+/-0.2 eV in the temperature range 320-400 degrees C, which suggests that the path for diffusion of Cu is along the Al/AlOx/SiOy interface for these single crystals. The apparent effective valence (Z*) characterizing electromigration was measured to be -5.4+/-1.2 at 350 degrees C. (C) 1999 American Institute of Physics. [S0003-6951(99)02401-8].