Method of forming bipolar transistor having substrate to polysilicon extrinsic base contact

A process for forming a bipolar transistor, comprising the steps of:

• providing a silicon substrate having a surface;
• implanting and diffusing a doped collector region having a first conductivity type, the doped collector region being formed within the silicon substrate and being exposed at the surface of the silicon substrate;
• growing a silicon dioxide layer overlying the substrate;
• depositing a first polysilicon layer overlying the first silicon dioxide layer;
• depositing a TEOS based layer overlying the first polysilicon layer;
• etching a portion of the silicon dioxide layer, a portion of the TEOS based layer, and a portion of the first polysilicon layer, the etching forming an exposed portion of the substrate which contains the doped collector region and forming a first polysilicon layer sidewall;
• implanting and diffusing a doped base region having a second conductivity type within the exposed portion of the substrate and overlying the doped collector region, the doped base region exposed at said surface of the substrate;
• growing a conductive epitaxially grown region laterally adjacent the first polysilicon layer sidewall and overlying the surface of the substrate;
• forming a first dielectric sidewall spacer laterally adjacent the conductive epitaxially grown region that is adjacent the first polysilicon layer;
• etching a portion of the conductive epitaxially grown region which overlies the surface of the substrate, the etching of the portion of the conductive epitaxially grown region forming a sidewall of the conductive epitaxially grown region;
• forming a second dielectric sidewall spacer laterally adjacent the sidewall of the conductive epitaxially grown region;
• and
• depositing a second polysilicon layer having the first conductivity type and overlying each of the substrate, the first and second dielectric sidewall spacers, and the TEOS based layer, the second polysilicon layer being electrically coupled to the substrate and at least partially forming a doped emitter region.