Effects of Substrate Thermal Characteristics on the Electromigration Behavior of Al Thin Film Conductors

Electromigration failure in aluminum conductors is strongly temperature activated, and reliable levels of current density do significantly raise the conductor temperature. However, the temperature increase and its ultimate effect on the conductor lifetime is related to device and substrate structure and to the pulsewidth and duty cycle of pulsed currents. This work describes simple but accurate models for thermal buildup in typical IC structures due to both constant and pulsed currents. The results are then included in predictive models for pulsed current electromigration lifetime. These models include temperature cycling and its effect on damage relaxation between pulses, and they are built up in a modular fashion from the basic constant current model. Experimental data is shown to support the theory.