Browse Prior Art Database

Particle Detection on Chromium or Phase Shifting Masks

IP.com Disclosure Number: IPCOM000116592D
Original Publication Date: 1995-Oct-01
Included in the Prior Art Database: 2005-Mar-30
Document File: 2 page(s) / 36K

Publishing Venue

IBM

Related People

Wagner, D: AUTHOR

Abstract

Pattern edges and critical particles on chromium or phase shifting masks may be highlighted by darkfield illumination methods. Disclosed is a way to find methods which allow to distinguish between pattern and particles.

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Particle Detection on Chromium or Phase Shifting Masks

      Pattern edges and critical particles on chromium or phase
shifting masks may be highlighted by darkfield illumination methods.
Disclosed is a way to find methods which allow to distinguish between
pattern and particles.

      A method for testing masks using darkfield reflection
illumination and darkfield transmission illumination is already
described (*).

      When inspecting phase shifting masks there is however to be
considered that generally the phase edges diffract more light than
the edges of chromium masks and that the Levenson-type masks show
parasitic edges in the backscattered light rendering improper the use
of a difference method.

      Shown in Fig. 2 is a method which is more sensitive than the
conventional dark field mask inspection method, shown in Fig. 1,
which
illuminates the mask from its glass side.

      When illuminating from the glass side the pellicle ring
prevents the collector to collect light.  Fig. 2 shows the
ring-shaped illumination of the mask.  The diffracted light is
collected by a circular aperture within the illumination area.  This
arrangement is working at its optimum when using an aperture as big
as possible.  Using a high numerical aperture produces the smallest
laser spot diameter for every wavelength, thus, increases the
sensitivity and the number of pixels.
  Reference
  (*) U.S. Patent 4,681,442.