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 lowe
r doping at the emitter edge due to known perimeter depletion and emit
ter plug effects (PPE's) leads to a reduced increase in base current p
er 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.