Process for making self-aligned polysilicon base contact in a bipolar junction transistor

摘要

A bipolar transistor in accordance with the invention includes a polysilicon base contact (607A) which is self-aligned with a polysilicon emitter (303). The polysilicon emitter is formed from a first polysilicon layer overlying an intrinsic base region (502) in a substrate (201). An extrinsic base (504) in the substrate is in contact with the intrinsic base and is self-aligned with a spacer (406) adjacent to the emitter. The polysilicon base contact is formed from a second polysilicon layer (407) in contact with the extrinsic base and overlying the emitter. A second sidewall spacer (508) is formed on the second polysilicon layer on step caused by the emitter. A protective layer (509, 510) formed on portions of the second polysilicon layer protects the base contact when the second spacer and the underlying portion of the second polysilicon layer are removed. The separation between the polysilicon base contact and the polysilicon emitter is controlled by the thickness the second polysilicon layer and the thickness of the spacers so that the base contact is self-aligned with a fixed separation from the emitter. Layer and spacer thicknesses define separation between the emitter and the base contact and permit sub-micron active regions in the substrate.