The influence of surface treatments on the electrical characteristics of polysilicon emitter bipolar transistors

Silicon bipolar transistors have been made with arsenic-implanted or phosphorus-diffused polysilicon emitters. The effects of different surface treatments, prior to polysilicon deposition, are investigated by comparing results obtained for a dip etch in hydrofluoric acid with those for an RCA clean. Detailed electrical results are presented for these two types of device, including transistor characteristics as a function of temperature. Rutherford backscattering is used to provide the arsenic profiles in the polysilicon and single-crystal silicon. It is shown that the dip etch devices have gains three times higher than conventional transistors, and a comparable temperature coefficient of the current gain. In contrast, the RCA devices have gains which are seven to thirty-two times higher than conventional transistors and a temperature coefficient which is superior. These results are explained using theoretical models from the literature.