Trade-off between emitter resistance and current gain inpolysilicon emitter bipolar transistors with intentionally growninterfacial oxide layers

Experimental measurements of emitter resistance and current gain in polysilicon emitter bipolar transistors that have received annealing to break up an intentionally grown RCA oxide interfacial layer are presented. An anneal of 900°C for 10 min in a nitrogen ambient of the interfacial layer prior to polysilicon doping resulted in a decrease in emitter resistance by approximately a factor of 5, with an increase in base saturation current of only 25% while still maintaining a current gain of around 500. The authors believe that this is the largest trade-off in emitter resistance versus current gain demonstrated so far for polysilicon transistors with an RCA interfacial layer. These results support a theory previously proposed by the authors (1991) predicting that significant trade-offs between emitter resistance and current gain can be obtained if an intentionally grown interfacial oxide layer in polysilicon emitter bipolar transistors is annealed so as to induce only partial breakup such that most of the layer remains intact