The use of an interface anneal to control the base current and emitter resistance of p-n-p polysilicon emitter bipolar transistors

The effects of an interface anneal on the electrical characteristics of p-n-p polysilicon-emitter bipolar transistors are reported. For devices with a deliberately grown interfacial oxide layer, an interface anneal at 1100 degrees C leads to a factor of 15 increase in base current, and a factor of 2.5 decrease in emitter resistance, compared with an unannealed control device. These results are compared with identical interface anneals performed on n-p-n devices, and it is shown that the increase in base current for p-n-p devices is considerably smaller than that for the n-p-n devices. This result is explained by the presence of fluorine in the p-n-p devices, which accelerates the breakup of the interfacial layer. >