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Elevated Emitter Junction for High Performance Bipolar Transistor

IP.com Disclosure Number: IPCOM000121897D
Original Publication Date: 1991-Oct-01
Included in the Prior Art Database: 2005-Apr-04
Document File: 2 page(s) / 50K

Publishing Venue

IBM

Related People

Ng, CC: AUTHOR [+3]

Abstract

In current self-aligned bipolar technology, the emitter is formed by diffusion from a doped polysilicon contact. The emitter junction contains a perimeter and an area component. We propose here a novel transistor in which the emitter is elevated, so it is above the substrate and surrounded by the sidewall. Thus, the perimeter component of the emitter-to-base junction capacitance is eliminated.

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Elevated Emitter Junction for High Performance Bipolar Transistor

      In current self-aligned bipolar technology, the emitter
is formed by diffusion from a doped polysilicon contact.  The emitter
junction contains a perimeter and an area component. We propose here
a novel transistor in which the emitter is elevated, so it is above
the substrate and surrounded by the sidewall.  Thus, the perimeter
component of the emitter-to-base junction capacitance is eliminated.

      In our proposed process, the intrinsic base and the collector
are implanted at low energies in order to achieve a narrow base
width.  After the sidewall is formed, there are two ways to form the
emitter.

      In the first approach, a thin and undoped Low Temperature
Epitaxial (LTE) silicon is deposited (see the figure).  The thickness
of this epitaxial layer is equal to the expected emitter junction
depth.  Then polysilicon is deposited over the LTE epitaxial layer.
The polysilicon is either doped in-situ or by ion implantation.  A
thermal anneal drives the dopants from the polysilicon into the LTE
layer to form the emitter.

      In the second approach, a thin and in-situ doped LTE is
deposited.  The thickness of the LTE is equal to the expected emitter
junction depth.  Then a layer of in-situ doped polysilicon is
deposited over the LTE epitaxial layer. Rapid thermal annealing is
then applied to activate the dopant.

      The advantages of our proposed elevated emitter tra...