Activation energy and prefactor for surface electromigration and void drift in Cu interconnects

Surface electromigration rates on oxide-free surfaces of unpassivated damascene Cu interconnect segments have been determined through electromigration testing under vacuum. Electromigration-induced voids grew at the cathode end of the segments due to a flux divergence at refractory-metal-lined vias to the lead lines below the test segment. Copper diffusivity on a clean Cu surface was determined by measuring the size of the voids as a function of time and test temperature at a fixed current. An activation energy of 0.45 +/- 0.11 eV and a prefactor of 3.35 x 10(-12) m(2)/s were found for the product of the effective charge z* and the surface diffusivity D-s. This result is shown to be consistent with void drift rates measured in passivated interconnects. (C) 2007 American Institute of Physics.