Acceleration parameters and reliability of SiGe HBTs during long-term forward-biased operation

We have conducted accelerated lifetesting on discrete HBTs fabricated with the IBM SiGe5HP HBT technology, and determined the dependence of the wear-out on emitter interconnect temperature and current density. The wearout occurred by degradation of DC current gain, β, caused by increase of the base current. The characteristics and the parametric dependences of the β degradation were consistent with an electromigration (EM) mechanism originally developed by IBM. EM in the emitter interconnects causes compressive stress on the emitter semiconductor sufficient to alter the semiconductor energy band structure, leading to an increase in base current and associated reduction in β. Utilizing our empirically determined acceleration parameters, we have estimated the worst-case expected changes in β during typical use conditions (125 °C, J_i=1.0 mA/μm²). The results showed that after 20 years β would degrade by approximately 17±1%. This degradation is insignificant for most IC applications, and we therefore conclude that this technology is highly reliable during long-term forward-active bias operation.