The electromigration failure of Al interconnect has been extensively studied under constant current conditions. Integrated circuits, however, often operate with unidirectional or bidirectional current pulses. The assumption is often made that the conductor lifetime under unipolar DC pulses increases linearly with the reciprocal of the duty factor (i.e., the total on-time to failure is the same in constant DC and pulsed DC experiments). This is based on the further assumption that damage is accumulated during on-time and there is no recovery during the off-time. However, experimental results show lifetime improvement that differs from that predicted by this simplified model. A model which includes the damage relaxation effect during the off-cycle of the pulse is proposed. The mass transport in the conductor is described, and the electromigration lifetime is related to the flux of vacancies. The frequency and duty factor dependence of the pulsed DC median time-to-failure can be determined and used is to predict pulsed DC lifetime using constant DC stressing results. Simulation results are presented and compared to experimental data.
|Number of pages||2|
|Journal||Digest of Technical Papers - Symposium on VLSI Technology|
|State||Published - 1 Dec 1988|