Native oxide free polycrystalline/single crystal Si interface obtained by in situ cleaning: e ffects on the electrical performances of polysilicon emitter transistors

We compare polysilicon emitter bipolar transistors fabricated by using di€erent treatments of the interface between single crystal and polycrystalline Si (polysilicon) in the emitter region. One of the treatments consisted in an in situ cleaning of the silicon surface performed in the deposition chamber prior to the polysilicon deposition, resulting in an oxide free interface. A detailed structural and electrical characterization of transistors with and without an oxide free interface is presented. It is shown that, even if common emitter current gain decrease is observed, a strong improvement of base resistance and breakdown voltage can be achieved, while maintaining noticeable high frequency characteristics.