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In-Situ Doped Tungsten Silicide

IP.com Disclosure Number: IPCOM000103522D
Original Publication Date: 1990-Dec-01
Included in the Prior Art Database: 2005-Mar-18
Document File: 1 page(s) / 42K

Publishing Venue

IBM

Related People

Joshi, RV: AUTHOR [+3]

Abstract

Tungsten silicide is often used in VLSI technology as, for example, a polycide structure (WSix on poly) in BIPOLAR applications. Tungsten silicide is deposited on p+ poly to form an extrinsic base to lower the contact resistance. If this structure is annealed, the underlying doped polysilicon loses 50 percent of its boron into the WSix layer. A technique is described whereby the processing required for this structure is simplified and dopant loss is reduced. This process overcomes the out-diffusion problem by in-situ boron doping the silicide and using it as a source to drive-in boron into the underlying polysilicon.

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In-Situ Doped Tungsten Silicide

      Tungsten silicide is often used in VLSI technology as, for
example, a polycide structure (WSix on poly) in BIPOLAR applications.
Tungsten silicide is deposited on p+ poly to form an extrinsic base
to lower the contact resistance.  If this structure is annealed, the
underlying doped polysilicon loses 50 percent of its boron into the
WSix layer.  A technique is described whereby the processing required
for this structure is simplified and dopant loss is reduced. This
process overcomes the out-diffusion problem by in-situ boron doping
the silicide and using it as a source to drive-in boron into the
underlying polysilicon.

      In-situ B doped WSix may be fabricated by the inclusion of up
to several percent diborane in the gaseous deposition source used to
deposit the silicide.  This prevents boron out-diffusion from the
underlying polysilicon.  In addition, the major difficulty in the
deposition of WSix is the poor efficiency with which silicon is
incorporated in the films. Although only small flows (10 sccm) of WF6
are required in commercial reactors, standard processing requires
very large flows (1000 sccm) of SiH4 to achieve the desired post
anneal film stoichiometry.  The use of diborane in the presence of
silane also significantly enhances the decomposition of silane and
reduces silane consumption to more reasonable levels.  Thus, in
summary, the in-situ boron doping of tungsten silicide eliminates
dopant loss problems...