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 struc tures subjected to unipolar or bipolar current stresses. Activation energy values were similar between AC and DC stress suggesting that the same failu re mechanisms occurred in both cases. From 100 Hz to 1 MHz, the results fol lowed an average current model for which the sample is stressed by an effic ient current density averaged over the period and Joule heating is taken in to account with an original thermal model. The average current model was al so 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 1 Hz, the results tend towa rd an on time model for which matter diffusion occurred only during the app lication of the current. (C) 1999 Elsevier Science Ltd. All rights reserved .