Perimeter Effects and Doping Conditions in Narrowemitter Silicon Bipolar Transistors

A reduced emitter doping concentration in silicon bipolar transistors with implanted emitter-polysilicon is often assumed to be the reason for the decrease of cut-off frequency in narrow-emitter devices. Therefore, perimeter effects and doping conditions in transistors with implanted as well as in-situ doped emitter-polysilicon are investigated. Detailed two-dimensional characterization shows that the deteriorated behaviour of narrow devices is mainly caused by the increase of the perimeter to area ratio (P/A) and not by insufficient emitter doping. It is demonstrated that transistors; even with emitters as narrow as 0.08 ¿m, can be fabricated without reduction in emitter doping concentration.