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Enhanced Schottky Barriers by C-Containing Plasma

IP.com Disclosure Number: IPCOM000108186D
Original Publication Date: 1992-Apr-01
Included in the Prior Art Database: 2005-Mar-22
Document File: 1 page(s) / 66K

Publishing Venue

IBM

Related People

Fleishman, A: AUTHOR [+3]

Abstract

The insensitivity of the Schottky barrier height (0.7 eV) on n-type GaAs irrespective of the contact material used is attributed to the pinning of Fermi level at the metal/GaAs interface. However, in some GaAs devices there is a need to increase the barrier height. An increase will allow a larger positive gate bias for enhancement mode MESFETs, thus permitting design of digital circuits with an improved noise margin and a relaxed tolerance on device threshold voltage meV) has been demonstrated by counter doping of the n-surface of GaAs either by Be or Mg implants. However, in either case, a significant redistribution of the implanted p-dopant occurs during postimplant anneal. The process, therefore, is not suitable for manufacturing.

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Enhanced Schottky Barriers by C-Containing Plasma

      The insensitivity of the Schottky barrier height (0.7 eV) on
n-type GaAs irrespective of the contact material used is attributed
to the pinning of Fermi level at the metal/GaAs interface.  However,
in some GaAs devices there is a need to increase the barrier height.
An increase will allow a larger positive gate bias for enhancement
mode MESFETs, thus permitting design of digital circuits with an
improved noise margin and a relaxed tolerance on device threshold
voltage meV) has been demonstrated by counter doping of the n-surface
of GaAs either by Be or Mg implants.  However, in either case, a
significant redistribution of the implanted p-dopant occurs during
postimplant anneal.  The process, therefore, is not suitable for
manufacturing.  It is becoming clear from recently published data
that implated C can give high hole concentrations (>N 1x1019 cm-3) in
GaAs and does not show any noticeable redistribution in GaAs during
post-implant anneal.

      This disclosure describes a novel way to achieve ultrashallow
C-doping at high concentrations (>N 1x1019cm-3) to fabricate p+
regions in the channel of a GaAs MESFET to obtain high Schottky
barriers.  The present method involves exposing the n-channel region
of a GaAs MESFET with a C-containing (e.g., CH4 or CF4) plasma prior
to the channel anneal.  Furthermore, the annealing will also allow
the H or F which is introduced during the plasma exposure to
outdiffu...