DEPENDENCE OF ELECTROMIGRATION RATE ON APPLIED ELECTRIC-POTENTIAL

Copper films, current stressed under in-situ, ultra-high vacuum (UHV), clean surface conditions,have an activation energy for electromigrati on that lies in the range of values obtained for surface diffusion. Re cent field ion microscope studies of {001} fee metal surfaces showed t hat an electric field applied to the surface can influence the rate of surface diffusion. In the present work, positive and negative potenti als were applied to copper stripes undergoing electromigration damage cinder UHV, clean surface conditions. Activation energies were measure d as a function of applied potential using an electrical resistance ch ange method. The results show a strong dependence of the activation en ergy for electromigration on the sign and magnitude of the applied pot entials. Positive potentials raise the activation energy while negativ e potentials lower it. These results are in agreement with what one wo uld expect from field ion microscopy electric field effect experiments . They may also have practical implications in possibly controlling th e rate of electromigration damage in:passivated metal interconnects us ed in microelectronics where the damage mechanisms may involve volume, grain boundary, interfacial and surface diffusion processes.