An investigation of the damage mechanisms in impact ionization-induced "mixed-mode" reliability stressing of scaled SiGe HBTs

A robust, time-dependent stress methodology for investigating "mixed-mode" (simultaneous high J/sub C/ and high V/sub CB/) reliability degradation in advanced SiGe HBTs is introduced. We present comprehensive stress data on scaled 120 GHz SiGe HBTs, and use specially designed test structures with variable emitter-to-shallow trench spacing to shed light on the resultant damage mechanisms. We also employ calibrated MEDICI simulations using the hot carrier injection current technique to better understand the damage mechanisms, and conclude by assessing the impact of mixed-mode stress in aggressively scaled 200 GHz SiGe HBTs.