Browse Prior Art Database

Dark Field Through the Lens Alignment for a Step And Repeat Camera

IP.com Disclosure Number: IPCOM000120842D
Original Publication Date: 1991-Jun-01
Included in the Prior Art Database: 2005-Apr-02
Document File: 2 page(s) / 80K

Publishing Venue

IBM

Related People

Tibbetts, RE: AUTHOR [+3]

Abstract

A modification is described of the automatic dark field optical alignment apparatus taught in U.S. Patent 4,232,969 for use in situations where there is insufficient room between the mask and the projection lens for the optical components described in the illustrative embodiment.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 52% of the total text.

Dark Field Through the Lens Alignment for a Step And Repeat Camera

      A modification is described of the automatic dark field
optical alignment apparatus taught in U.S. Patent 4,232,969 for use
in situations where there is insufficient room between the mask and
the projection lens for the optical components described in the
illustrative embodiment.

      The present embodiment includes a separate illuminator (at
least one, if rotational alignment is not required), a removable
mirror, a mirror with a hole in an image plane of the aperture stop
of the system and additional image forming optics.

      The projection lens, when used at one half of its numerical
aperture, will have a line spread function width of 2g/N.A.  For a .4
N.A. lens at 5X, this corresponds to an opening in the mask of 10 mm.
At full N.A., this opening would be only 5 mm (g/UR and g/UI in the
drawing).  The dark field light which is scattered by the edges of
the alignment aids on the wafer will, therefore, pass through the
central half width of the slit.  It is then separated from the
illuminating light in the parallel path (see the top righthand side
of the drawing).  An optional field lens 4, just above the mask,
images the beam separating element onto the lens pupil, thus
optically superposing both.

      Critical illumination may be used in this system since only a
small area must be filled with light, while uniform filling of the
pupil is of primary importance.  Thus, lenses 1 and 2...