Method of forming high performance bipolar transistor

A method of a fabricating a bipolar transistor structure in a semiconductor substrate that includes a substrate active device region, a dielectric isolation structure formed at the periphery of the active device region, the method comprising:

• removing an upper portion of the active device region to define an upper surface region of the active device such that a recess is defined above the upper surface region;
• introducing dopant into the upper surface region to define a collector region having a first conductivity type;
• depositing a epitaxial layer of silicon-germanium (SiGe) that fills the recess above the upper surface region;
• planarizing the SiGe epitaxial layer such that an upper surface of the SiGe epitaxial layer is substantially coplanar with an upper surface of the dielectric isolation structure, the planarized SiGe epitaxial layer defining a base region;
• forming a pad of dielectric material that extends from an edge of the dielectric isolation structure over a first portion of the base region such that a second portion of the base region is exposed;
• forming a layer of doped emitter polysilicon over the pad of dielectric material and the exposed second portion of the base region;
• patterning the layer of emitter polysilicon to define a ridge of emitter polysilicon having the first conductivity type and forms a ridge that extends beyond an edge of the pad of dielectric material, the ridge being in contact with the base regions;
• causing dopant to diffuse from the emitter polysilicon ridge into the base region to define an emitter-base junction in the base region;
• forming an oxide layer over the structure resulting from the foregoing steps;
• forming a layer of silicon nitride on the oxide layer;
• anisotropically etching the silicon nitride layer to stop on the oxide layer,
• whereby defining a silicon nitride sidewall spacer at an edge of the emitter polysilicon ridge and spaced-apart wherefrom by an intervening portion of the oxide layer;
• and
• removing exposed portions of the oxide layer.