Jennifer Passage, Research Assistant, SUNY Polytechnic Institute               

Jennifer (Shuster) Passage has received her Bachelor of Arts in the study of Mathematics from the College of St. Rose from Albany, NY in 2013. She is currently pursuing Ph.D. degree with the Colleges of Nanoscale Science and Engineering, SUNY Polytechnic Institute. She has worked on projects involving the time dependent breakdown of low-k materials in the BEOL, as well as intermittent current studies of copper in the BEOL.

Enhanced Lifetime of Copper Interconnect Lines Due to Stress Relaxation During Intermittent Current Studies

Electromigration testing is generally performed via the application of a constant direct current.  However, in “real life” the conductor is subjected to an alternating current or pulsed DC sometimes with a low duty cycle. If at all, compensation for pulsed operation is treated “time on,” where the duty cycle is modelled as a linear multiplier of the lifetime. However, electromigration lifetime is determined by the electromigration driving force and an induced stress gradient driving force. The electromigration driving force produces a counter force in the form of a stress gradient. Damage occurs when there is enough stress to nucleate a void. It makes sense that turning off the current periodically should provide some relaxation of the stress gradient and contribute to a longer lifetime than if the current were uninterrupted DC. In this experiment, we studied the electromigration failure of copper interconnects using intermittent current at a previously neglected very low frequency, 10 Hz, with FormFactor’s new module capable of intermittent electromigration stressing. The effects of temperature and duty cycle were studied and compared to earlier studies. Evidence of stress relaxation was revealed in significantly longer lifetimes than expected if “time on” were the only criterion for damage creation. The consequences for extrapolation of lifetimes from accelerated to use conditions is discussed.