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

We compare polysilicon emitter bipolar transistors fabricated by using diff erent treatments of the interface between single crystal and polycrystallin e Si (polysilicon) in the emitter region, One of the treatments consisted i n an in situ cleaning of the silicon surface performed in the deposition ch amber prior to the polysilicon deposition, resulting in an oxide free inter face. A detailed structural and electrical characterization of transistors with and without an oxide free interface is presented. It is shown that, ev en if common emitter current gain decrease is observed. a strong improvemen t of base resistance and breakdown voltage can be achieved, while maintaini ng noticeable high frequency characteristics. (C) 1999 Elsevier Science Ltd . All rights reserved.