Bipolar transistor with ultra small self-aligned polysilicon emitter and method of forming the transistor
AssigneeNational Semiconductor Corporation
InventorAbdalla Aly Naem
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Abstract
A low-power bipolar transistor is formed to have an intrinsic emitter region with a sub-lithographic width, and an oxide layer that is self aligned to an overlying extrinsic emitter. The small extrinsic emitter region reduces the maximum current that can flow through the transistor, while the self-aligned oxide layer and extrinsic emitter reduces the base-to-emitter junction size and device performance variability across the wafer.
Claims27
A method for forming a bipolar transistor on a wafer, the wafer having a buried layer, an epitaxial layer of a first conductivity type formed over the buried layer and having a smaller dopant concentration than the buried layer, and an intrinsic base region of a second conductivity type formed in the epitaxial layer, the method comprising the steps of:
- forming an isolation region on the intrinsic base region;
- forming a layer of conductive material on the isolation region and the intrinsic base region;
- etching the layer of conductive material to form an extrinsic emitter on the isolation region and the intrinsic base region;
- forming an intrinsic emitter region in the intrinsic base region;
- and
- forming a side-wall spacer on the intrinsic base region to adjoin the extrinsic emitter.
A method for forming a bipolar transistor on a wafer, the wafer having a substrate, an epitaxial layer of a first conductivity type formed over the substrate, and a base region of a second conductivity type formed in the epitaxial layer, the base region having a top surface, the method comprising the steps of:
- forming an isolation region, the isolation region contacting the top surface of base region;
- forming a layer of conductive material on the isolation region and the base region;
- etching the layer of conductive material to form an emitter, the emitter contacting the base region of the epitaxial layer, and having the first conductivity type;
- and
- forming a side wall spacer on the base region to contact the emitter.
Dependencies are inferred from the claim text.