Bipolar transistor with raised extrinsic self-aligned base using selective epitaxial growth for BiCMOS integration

High performance bipolar transistors with raised extrinsic self-aligned base are integrated into a BiCMOS structure containing CMOS devices. By forming pad layers and raising the height of an intrinsic base layer relative to the source and drain of preexisting CMOS devices and by forming an extrinsic base through selective epitaxy, the effect of topographical variations is minimized during a lithographic patterning of the extrinsic base. Also, by not employing any chemical mechanical planarization process during the fabrication of the bipolar structures, complexity of process integration is reduced. Internal spacers or external spacers may be formed to isolate the base from the emitter. The pad layers, the intrinsic base layer, and the extrinsic base layer form a mesa structure with coincident outer sidewall surfaces.