Browse Prior Art Database

Illuminating Equipment for Overlay Measurement

IP.com Disclosure Number: IPCOM000118178D
Original Publication Date: 1996-Oct-01
Included in the Prior Art Database: 2005-Apr-01
Document File: 2 page(s) / 56K

Publishing Venue

IBM

Related People

Wagner, D: AUTHOR

Abstract

Disclosed is a laser illumination equipment with a cross-shaped intensity distribution in the image plane and in the aperture plane. This intensity distribution improves the signal-to-noise ratio and provides low radiation intensity at the surface of a wafer to be measured.

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Illuminating Equipment for Overlay Measurement

      Disclosed is a laser illumination equipment with a cross-shaped
intensity distribution in the image plane and in the aperture plane.
This intensity distribution improves the signal-to-noise ratio  and
provides low radiation intensity at the surface of a wafer to be
measured.

      The illumination equipment for future chip generations will be
scanning steppers.  This requires frequent overlay measurements with
high accuracy which is only achievable with a significantly improved
signal-to-noise ratio.  Conventional overlay measuring equipment uses
white light illumination with the radiation intensity of the lamps
being limited.

      The illumination equipment disclosed comprises twenty detectors
in the aperture plane.  The cross-shaped arrangement of these
detectors covers a cross-shaped portion of the aperture plane.  Each
detector is  sufficiently provided with light to reach the required
signal-to-noise ratio.

      Overlay measurements may ideally be carried out by two
orthogonal scanning apertures.  The interference contrast needs a
cross-shaped intensity distribution in the aperture plane and also in
the image plane.  According to the ratio aperture width to aperture
length, the radiation intensity in the image plane is reduced without
affecting the signal-to-noise ratio.

      Suitable light emitting sources are laser diodes with an
effective length-to-width ratio of about 20:1.  Th...