Secondary ion mass spectrometry (SIMS) applications on characterization of RF NPN bipolar polysilicon emitter process

摘要

The device design for the cutting edge RF npn bipolar polysilicon emitter transistrors (PETs) is required to reduce the volume of N~+ emitter single crystal region and the vertical width of the p-type base region. In addition, due to the extremetly sensitive nature of the interface between polysilicon/monosilicon, a well controlled and characterized interface plays a key role in fabricating reproducible PETs. SIMS measurements of the interfacial oxide have established a very good correlation between the interfacial oxide thickness and the device h_(FE) performance. The reduction of the interfacial oxide from 7-8 A to 3-4 A results in a controllable h_(FE) (current gain) with very uniform distribution within wafer and very good reproducibility. Furthermore, the experimental results have shown that a total elimination of the interfacial oxide by in-situ polysilicon deposition coupled with H_2 bakig resulted in a complete epitaxial realignment of polycrystalline silicon to the underlying single crystal silicon. This single crystal emitter contact prevented efficient arsenic diffusion into substrate to form the critical n~+ emitter single crystal region.