Failures induced by electromigration in ECL 100k devices

Reliability of ECL 100k devices using Al (4%wt Cu, 1%wt Si) double level metallization, isoplanar technology with shallow, 0.25 μm, base-emitter junctions was evaluated by means of high current and high temperature stresses. Three failure modes connected with electromigration phenomena were found in the output transistor: (a) base-emitter shunts owing to junction spiking caused by Al-Si interdiffusion enhanced by electromigration; (b) collector-emitter shorts due to the breaking of the dielectric oxide between two superimposed metal levels owing to material transport and pile-up in the underlying metallization; (c) open circuit of the output emitter due to void growth in the Cu-depleted areas of the Al interconnections. After B-E shunts, failure mechanism evolves towards two different sequences of failure modes, according to the different transistor structures; in fact C-E shorts were found to occur only when collector and emitter metals are superimposed, while the open circuit of the output emitter is the final failure for all configurations. The earlier and more frequent failure mode observed is the resistive shunt of the base-emitter junction of the output transistor, in agreement with previously reported data on electromigration effects in Al (Cu, Si) metallizations used both as interconnections and as contacts to shallow junctions.