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Continuous Gettering of Contaminants Using Multiple Polysilicon Films

IP.com Disclosure Number: IPCOM000120394D
Original Publication Date: 1991-Apr-01
Included in the Prior Art Database: 2005-Apr-02
Document File: 2 page(s) / 84K

Publishing Venue

IBM

Related People

Tice, WK: AUTHOR [+2]

Abstract

A phosphorous-doped, polycrystalline silicon (polysilicon) thin film, deposited on the backside of silicon wafers, can be used for gettering of metal impurities to improve device reliability and yields. The gettering is chiefly accomplished by dislocations situated at the polysilicon film/silicon single crystal interface, and also along polysilicon grain boundaries. The efficiency of a single layer polysilicon film to getter is diminished during high temperature processing due to elimination of interfacial dislocations by epitaxial growth of the thin film of silicon upon the single crystal silicon substrate, and reduction of grain boundary area.

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Continuous Gettering of Contaminants Using Multiple Polysilicon Films

      A phosphorous-doped, polycrystalline silicon
(polysilicon) thin film, deposited on the backside of silicon wafers,
can be used for gettering of metal impurities to improve device
reliability and yields.  The gettering is chiefly accomplished by
dislocations situated at the polysilicon film/silicon single crystal
interface, and also along polysilicon grain boundaries.  The
efficiency of a single layer polysilicon film to getter is diminished
during high temperature processing due to elimination of interfacial
dislocations by epitaxial growth of the thin film of silicon upon the
single crystal silicon substrate, and reduction of grain boundary
area.

      This article teaches that gettering capacity can be rejuvenated
during processing by deposition of additional layers of polysilicon.
Such layers are added to the backside of a wafer during processing,
when polysilicon is used to build an integrated circuit.  Some key
steps are necessary to ensure that additional polysilicon layers can
act as efficient gettering materials.  First, intimate contact
between the initial, backside polysilicon layer and second layer must
be made.  This may require the removal of previously deposited, or
grown, dielectric materials which can be conveniently removed with a
dry etching step, and an over etch into the initial polysilicon film
ought to be done to insure complete removal.  Any additional
polysilicon would then be added as part of the normal process flow.
Subsequent to deposition of a second polysilicon layer, oxide layers
thinner than 20-30 angstroms can also be rendered harmless by high
temperature annealing, which causes the original continuous film to
fragment by diffusion of oxide into islands.  In this way, a
reduction of energy comes about by a decrease in the total area of
the oxide/silicon interface.

      These additional polysilicon layers coul...