On the very-high-current degradations on Si n-p-n transistors

The stressing of 0.8-μm double-poly self-aligned Si n-p-n transistors at current densities up to 12.5 mA/μm² is discussed. The emitter contact does not fail abruptly; rather, its contact resistance drifts gradually. The contact resistance increases when the current flows out of the emitter and decreases when the current is reversed. The drift in emitter resistance can be thermally accelerated and is consistent with the electromigration phenomenon. The emitter-base junction shows negligible degradation when stressed in normal-mode operation, i.e. the current flows out of the emitter. However, the junction degrades when stressed with open collector or when stressed in inverse mode. The annealing experiments show that the junction degradation results from the interface-state generation. However, the drift in contact resistance cannot be recovered by annealing. The causes of junction degradation are suggested