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Bipolar Transistors with Poly-SiGe Emitter Contacts and/or Poly-SiGe Extrinsic Bases

IP.com Disclosure Number: IPCOM000105769D
Original Publication Date: 1993-Sep-01
Included in the Prior Art Database: 2005-Mar-20
Document File: 2 page(s) / 44K

Publishing Venue

IBM

Related People

Crabb, EF: AUTHOR [+3]

Abstract

Disclosed are devices using poly-SiGe instead of polysilicon for the emitter and/or base contacts to reduce series resistances.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 64% of the total text.

Bipolar Transistors with Poly-SiGe Emitter Contacts and/or Poly-SiGe Extrinsic Bases

      Disclosed are devices using poly-SiGe instead of polysilicon
for the emitter and/or base contacts to reduce series resistances.

      Polysilicon emitter contacts offer significant advantages such
as self-aligned very shallow emitters and reduction of the base
current compared to metal-contacted devices.  There is in general a
trade-off between the reduction in base current and the emitter
resistance which is critically dependent on the emitter thermal cycle
and the polysilicon doping.  For sub-0.5&mu.m emitter devices, the
emitter resistance plays a major role in circuit operation.
Alternative emitter contacts which DECOUPLE the base current from the
emitter resistance, allow a significant reduction in emitter
resistance; therefore, are of great interest.

      The invention disclosed here replaces the polysilicon contact
to the emitter by poly-SiGe with typically 50% Ge.  The large Ge
fraction in the film insures higher dopant activation, higher
mobility and larger grain size which all lead to a reduction of two
components of the emitter resistance, the bulk poly resistance and
the metal/poly contact resistance.  Furthermore, a higher effective
surface recombination velocity for holes is expected at the
Si/Poly-SiGe interface, leading to a reduction of current gain.  This
feature is attractive for SiGe-base HBT applications in which the
current gain is too high, r...