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Emitter Structure for Optimum Bipolar Performance in BiCMOS

IP.com Disclosure Number: IPCOM000113704D
Original Publication Date: 1994-Sep-01
Included in the Prior Art Database: 2005-Mar-27
Document File: 2 page(s) / 42K

Publishing Venue

IBM

Related People

Hook, TB: AUTHOR [+3]

Abstract

An improved BiCMOS process is described in which the conventional PFET source/drain implant is prevented from entering the n-type NPN polysilicon emitter and limiting the performance of the NPN device.

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This is the abbreviated version, containing approximately 98% of the total text.

Emitter Structure for Optimum Bipolar Performance in BiCMOS

      An improved BiCMOS process is described in which the
conventional PFET source/drain implant is prevented from entering the
n-type NPN polysilicon emitter and limiting the performance of the
NPN device.

      The conventional BiCMOS process is shown in Fig. 1 just prior
to the introduction of the source/drain dopants.  No protection is
provided for the NPN emitter region so that subsequent source/drain
dopants will be implanted into the polysilicon emitter.

      The improved BiCMOS process is shown in Fig. 2.  A blocking
material such as silicon nitride was deposited uniformly over the top
of the gate polysilicon, and the entire stack was etched when the
gates were defined.  The blocking material left on top of the NPN
emitter (shown by cross-hatching) is thick enough to contain nearly
all of the subsequently implanted source/drain dopant.  The spacer
etch was designed so as to leave the blocking material intact over
the NPN emitter after spacer etch.  The spacer material may be
silicon dioxide.

      In Fig. 3, the improved BiCMOS process is shown after removal
of the blocking material and after silicidation of the polysilicon.
It is not necessary to remove the blocking material if salicidation
is not desired.  The resulting NPN emitter polysilicon is essentially
devoid of the source/drain dopant.  The emitter resistance and
bipolar
gain that result are better than that of the conve...