The effect of isolation edge profile on the leakage and breakdown characteristics of advanced bipolar transistors

The authors describe the effect of the isolation edge profile on the leakage and breakdown characteristics of advanced poly emitter NPN bipolar transistors. It is shown that the isolation edge profile can cause considerable base narrowing and reduction of the Gummel number, thus controlling the collector-emitter breakdown voltage, BV _ceo, and the collector-emitter leakage current, I _ceo. The reduction in BV_ceo can become severe enough so that the devices cannot operate at the maximum supply voltages used in emitter coupled logic (ECL) and BiCMOS circuits. The vertical scaling of the intrinsic device will be constrained under these circumstances to meet the required circuit breakdown characteristics, compromising device parameters such as beta and the unity gain cutoff frequency. Therefore device isolation can control key device parameters, thus becoming a major limiting factor in the development of high-performance bipolar devices