An Advancement in Transistor Second Breakdown Performance Using Molybdenum Metalization

Transistor second breakdown failures usually appear as collector-emitter short circuits. Microscopic examination of these devices shows that the contact metalization has undergone physical change. Cross sectioning shows that the short circuit is the result of the contact metal melting and alloying into the device. If it is assumed that second breakdown itself is not destructive but leads to the melting and alloying of the contact metalization, then a high temperature metal should be superior to aluminum for withstanding hot spots. This paper describes the experimental results of transistors having molybdenum-aluminum metalization compared to devices with only aluminum contacts. The results indicate that devices with molybdenum, when driven into second breakdown, will outlive aluminum units with respect to current by a factor of three.