ELECTROMIGRATION, STRESSES, AND PULSE EFFECTS IN THIN-FILM CONDUCTORS

It is theoretically shown that electromigration can lead to the formation of high electrodiffusional mechanical stresses in a thin‐film conductor and a stress gradient along it. The integrodifferential equation with partial derivative determined at one point is obtained and solved. The equation describes the process of mechanical stress gradient build‐up (relaxation). It is shown that this equation can be reduced to the equation of diffusion by proper choice of the boundary conditions, the relaxation time constant te is independent of the electric current density and determined by the mechanical and diffusional properties of the conductor material, its structural and geometric parameters, and temperature. For pulsating current, the mass flow increases with decreasing pulse duration and reaches a maximum when the pulse duration becomes less that the critical value τmax = (10−3 to 10−2)te. The projections'growth on a conductor during electromigration is caused by relaxation of electrodiffusional stress exceeding the yield limit of thin films. Copyright © 1990 WILEY‐VCH Verlag GmbH & Co. KGaA