Dependence of electromigration rate on applied electric potential

Abstract

Copper films, current stressed under in-situ, ultra-high vacuum (UHV), clean surface conditions, have an activation energy for electromigration that lies in the range of values obtained for surface diffusion. Recent field ion microscope studies of {001} fcc metal surfaces showed that an electric field applied to the surface can influence the rate of surface diffusion. In the present work, positive and negative potentials were applied to copper stripes undergoing electromigration damage under UHV, clean surface conditions. Activation energies were measured as a function of applied potential using an electrical resistance change method. The results show a strong dependence of the activation energy for electromigration on the sign and magnitude of the applied potentials. Positive potentials raise the activation energy while negative potentials lower it. These results are in agreement with what one would expect from field ion microscopy electric field effect experiments. They may also have practical implications in possibly controlling the rate of electromigration damage in passivated metal interconnects used in microelectronics where the damage mechanisms may involve volume, grain boundary, interfacial and surface diffusion processes.