Browse Prior Art Database

Three-Stage Single-Wafer Lift-Off Etch

IP.com Disclosure Number: IPCOM000101787D
Original Publication Date: 1990-Sep-01
Included in the Prior Art Database: 2005-Mar-16
Document File: 4 page(s) / 163K

Publishing Venue

IBM

Related People

Cunningham, CW: AUTHOR [+4]

Abstract

Undercut profiles in thick polymer films are usually needed when defining interconnecting metal lines and studs using the "lift-off" technique. The ideal profile needs to be vertical, to prevent it from contacting an adjacent pattern, and without a "foot" to achieve a successful lifting of the polymer stencil after metal deposition. The "foot" refers to the shaping of the etched profile at the bottom of the pattern. The non-ideal etched profile with the foot is shown in the figure.

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Three-Stage Single-Wafer Lift-Off Etch

       Undercut profiles in thick polymer films are usually
needed when defining interconnecting metal lines and studs using the
"lift-off" technique.  The ideal profile needs to be vertical, to
prevent it from contacting an adjacent pattern, and without a "foot"
to achieve a successful lifting of the polymer stencil after metal
deposition.  The "foot" refers to the shaping of the etched profile
at the bottom of the pattern.  The non-ideal etched profile with the
foot is shown in the figure.

      A nearly ideal profile is normally accomplished by etching the
polymer film at low pressures of less than 100 mtorr in an oxygen
plasma.  Since the etch rates at these pressures are rather low
(approximately 0.1 u/min), processing is usually done in a batch
mode.  In recent years, processing in the single-wafer mode is
becoming more manufacturable due to advantages of improved process
control and elimination of process scale up.  "Elimination of process
scale-up" refers to doing away with extensive re-optimization work
needed when a process is transferred from the laboratory to
manufacturing.  All process development in the laboratory is done
using one wafer at a time, due to cost and unavailability of large
number of partially processed wafers.  Most plasma etching processes
are sensitive to the number of wafers processed at a time (i.e.,
batch size), and the single wafer process has to be re-optimized or
completely redefined for successful etching of a batch.  Much time
and money is therefore expended for scale-up of lab processes, to
make them manufacturable in the batch mode.

      Single-wafer processing eliminates these scale-up activities
entirely, because processes developed in the laboratory now become
directly transferable due to similar single-wafer reactors being used
in manufacturing.  This technology therefore contributes to
significant savings in cost and time during technology transfer.
However, to keep the productivity comparable to batch etching,
single-wafer etching is done at high pressures to achieve high etch
rates (greater than 1 u/minute).  Although high-pressure single-wafer
reactors offer the advantages of being simple and cost effective,
they suffer from the drawback of producing "bowed" profiles in
polymers, as shown in the figure.  This effect is due to ion-neutral
scattering in the sheath adjacent to the wafer, causing the ions to
strike the sidewalls of the patterns and enhancing the lateral etch
rate.  This is also illustrated in the figure.

      The invention described here proposes a process to overcome
above limitation and achieve the right profile as required for
lift-off patterning.  The degree of verticalness that can be obtained
in etching a polymer using an oxygen plasma depends on the ratio of
the concentration of 02(+) ions to 0 atoms, since these two species
basically control the etching process.  The higher the 02(+)0 ratio,
the hi...