Image Number 11 for United States Patent #6004855.
A process for producing a small shallow-depth high-performance bipolar structure having low parasitic capacitance is disclosed wherein an active base region of a P-type material is first defined in a substrate, a portion of which is of N-type material in a device formation area surrounded by an isolating oxide regions, such as trenches or the like. An N-doped polysilicon layer is then defined over the active base region and over field oxide regions located atop the isolating trenches. This N-poly region, when treated, will provide an interdigitated collector with self aligning emitter region aligned over the active base region. After appropriate spaced isolation layers are placed, a P-poly layer is laid down and heat treated to cause the P-type doping material to diffuse into the substrate contact to the active base region. A thin buried collector layer, approximately 1.5- to 2-micron thick, can be used as a result of the combination of an interdigitated collector design and a thin epitaxial region in which the active base is located; this combination contributing to a low effective collector resistance that compensates for the increased resistance associated with a thinner buried collector layer. The process provides for collector contacts in close proximity to the active device region permitting fabrication of a small device with very low parasitic capacitance.