Control of polysilicon emitter interface using RTCVD

The device characteristics of n-p-n poly-emitter bipolar transistors under a variety of interface control schemes have been studied. Common emitter current gain, reverse bias emitter/base leakage current and emitter resistance parameters have been measured. Polysilicon emitter contacts were deposited in a RTCVD reactor, with and without an in-situ interface treatment step, using SiH IH2 chemistry at 4 torr total pressure. Further, the effect of a 30:1 HF dip, prior to loading the wafers into the load-lock, was also investigated. It is concluded that the behavior of the NPN transistors has a direct correlation with the polysilicon microstructure and interfacial oxide layer which is primarily influenced by the interface treatment process. The highest current gain and lowest emitter/base leakage current was obtained for the samples with a cleaned/oxidized polysilicon/silicon interface.

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