Browse Prior Art Database

Alignment Mark Annealing

IP.com Disclosure Number: IPCOM000105420D
Original Publication Date: 1993-Jul-01
Included in the Prior Art Database: 2005-Mar-19
Document File: 2 page(s) / 60K

Publishing Venue

IBM

Related People

Chiu, G: AUTHOR

Abstract

A method is disclosed for improvement of alignment signals in the presence of grainy alignment marks that scatter the light. The wafer or substrate is subject first to a laser annealing step. The grain boundaries can largely be annealed out and thus improve the signal to noise ratio of the alignment signal.

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Alignment Mark Annealing

      A method is disclosed for improvement of alignment signals in
the presence of grainy alignment marks that scatter the light.  The
wafer or substrate is subject first to a laser annealing step.  The
grain boundaries can largely be annealed out and thus improve the
signal to noise ratio of the alignment signal.

      The alignment marks, depending on the processes, can be very
grainy (e.g., Al films).  The dark-field alignment [1]  uses the
scattered light as its alignment signal.  It is especially vulnerable
to the light scattered by the grainy films, i.e., the scattered light
by the grain boundaries aggravates the noise level of the alignment
signal.  Even in the grating alignment method [2]  the scattered
light also degrades the alignment accuracy [3].

      The laser annealing can coalesce fine grains and thereby
drastically reduce the number of grain boundaries [4]  The
signal-to-noise ratio of the alignment signal can be improved in the
absence of scattered light from grainy films.  In this approach, the
alignment marks and only the alignment marks are subject to the laser
annealing.  The devices on the wafer are not exposed to or affected
by the laser beam.  The alignment accuracy is ultimately limited by
the signal-to-noise ratio of the alignment signal.  Therefore it is
important to reduce the noise due to the unwanted scattered light.

      High power lasers at 308nm (XeCl) or other wavelengths that are
absorbed by the grainy films can be used for laser annealing.  A
laser beam with limited to a field size lightly greater than the
alignment mark can be used to anneal one mark at a time, and then
step to other...