RELIABILITY IMPOSED DESIGN ASPECTS OF SUBMICROMETER POLYSILICON-EMITTER BIPOLAR-TRANSISTORS

The device reliability of narrow poly-emitter bipolar transistors with very shallow emitter junctions is studied experimentally. The excess base current due to nonuniform poly doping, which is typically seen in such devices, is found not to accelerate device degradation. The lower doping at the emitter edge due to known perimeter depletion and emitter plug effects (PPE's) leads to a reduced increase in base current per perimeter length with stress. The results show that bipolar device scaling can likely be pursued to a point where PPE's start to appear, and that lateral emitter grading is effective in improving the device reliability.