Effects of Pulse Duration and Polarity on the Electromigration Behavior of Copper Interconnects under Pulsed Current Stress

Abstract

ABSTRACTDirect current (D.C.) is usually employed to characterize the electromigration reliability of interconnects. However, D.C. characterization techniques might not reflect the actual reliability of interconnects that are carrying pulsed D.C. or A.C. (alternating current) signals during operation. This study investigates the effects of unipolar and bipolar pulsed current on the electromigration lifetime of copper (Cu) interconnects. A series of long period pulsed current (i.e. 2, 16, 32 and 48 hours) were applied to Cu interconnects. Lifetime enhancement is observed when the half-period of pulsed current is shorter than the medium-time-to-failure (t50) of D.C. stressed samples. Minor increase in resistance occurring in-between pulses for unipolar pulsed current stressed samples, and occurrence of damage healing in bipolar pulsed current stressed samples are reasons attributed for the observed enhanced lifetime. We obtained longer MTF when the period of the pulsed current is shorter.