Browse Prior Art Database

Laser Scan Microscopy with Increased Contrast

IP.com Disclosure Number: IPCOM000116796D
Original Publication Date: 1995-Nov-01
Included in the Prior Art Database: 2005-Mar-31
Document File: 2 page(s) / 37K

Publishing Venue

IBM

Related People

Wagner, D: AUTHOR

Abstract

Disclosed is a method which increases the interference contrast of a microscope by using a detector array. This allows to carry out overlay measurements with higher precision.

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Laser Scan Microscopy with Increased Contrast

      Disclosed is a method which increases the interference contrast
of a microscope by using a detector array.  This allows to carry out
overlay measurements with higher precision.

      Although having a 3 sigma value of 1 nm laser scanners for
linewidth detection could not be used for overlay measurements due to
the low contrast in the various layers caused by the monochromatic
illumination.  The laser scanning apparatus shown integrates the
various contrast enhancing methods developped for conventional
microscopes comprizing bright field, dark field, phase contrast and
differential interference contrast.

      In a laser scanner, normally the whole aperture is uniformly
illuminated and with the same aperture the image is formed on the
detector.  This provides a broad band of incident angles and the
interference contrast is flattened.

      With a ring-shaped aperture in the focal plane of the objective
and a ring-shaped detector illumination occurs within a small range
of angles and detection occurs within the same small range of angles.
Different incident angles are obtained by the use of ring-shaped
apertures of different sizes for the illumination and by the use of
ring-shaped detectors of different sizes.