Influence of pulsed DC current stress on Electromigration results in AlCu interconnections ; analysis of thermal and healing effects

Electromigration experiments have been performed on AlCu interconnect structures subjected to unipolar or bipolar current stresses. Activation energy values were similar between AC and DC stress suggesting that the same failure mechanisms occurred in both cases. From 100 Hz to l MHz, the results followed an average current model for which the sample is stressed by an efficient current density averaged over the period and Joule heating is taken into account with an original thermal model. The average current model was also verified for bipolar currents and provided very large increase of median time to failure when symmetric signals were considered. Asymmetric signals lead to unipolar electromigration behavior. At l Hz, the results tend toward an on time model for which matter diffusion occurred only during the application of the current. © 1999 Elsevier Science Ltd, All rights reserved.