Browse Prior Art Database

Aluminum Oxide Block-Out Mask for VLSI Lithography

IP.com Disclosure Number: IPCOM000119433D
Original Publication Date: 1991-Jan-01
Included in the Prior Art Database: 2005-Apr-01
Document File: 1 page(s) / 39K

Publishing Venue

IBM

Related People

Fredericks, EC: AUTHOR [+2]

Abstract

Advanced lithography tools, such as multi-reticle stepper, use a "through reticle (mask)/through lens" technique to align masks to the wafers. The alignment marks are usually located near the areas of the active devices. Resist in these areas is developed after the exposure, which can result in a metal shorting problem caused by poor sidewall definition of the alignment mark areas in a process which uses a deep trench etch followed by a metal deposition.

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Aluminum Oxide Block-Out Mask for VLSI Lithography

      Advanced lithography tools, such as multi-reticle stepper, use
a "through reticle (mask)/through lens" technique to align masks to
the wafers.  The alignment marks are usually located near the areas
of the active devices.  Resist in these areas is developed after the
exposure, which can result in a metal shorting problem caused by poor
sidewall definition of the alignment mark areas in a process which
uses a deep trench etch followed by a metal deposition.

      This problem can be solved by covering the alignment marks with
a blockout mask of an ultraviolet (U.V.) light transparent layer of
A12O3 about 1000 angstroms thick. A12O3 can be deposited either by
E-Beam evaporation or CVD deposition.  This block-out mask can be
formed by a conventional lift-off method using resist or polyimide as
a lift-off structure.  As the A12O3 layer has a very low etch rate in
CF4 plasma, selectivity of SiO2 to A12O3 is about 50:1.  Therefore,
it can protect the alignment mark areas from being attacked during
the subsequent etch process (see FIG. #1).

      The A12O3 is a stable dielectric material both thermally and
chemically.  It can be annealed at 750o for 30 minutes with no sign
of degradation, and an etchant of H3PO4/H2O2/Cr2O3, A12O3 can be
selectively removed with no trace of residual aluminum.

      Disclosed anonymously.