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Confocal Scanning Optical System for Overlay And Focus Control of Exposure Tools

IP.com Disclosure Number: IPCOM000100665D
Original Publication Date: 1990-May-01
Included in the Prior Art Database: 2005-Mar-16
Document File: 1 page(s) / 38K

Publishing Venue

IBM

Related People

Holmes, SJ: AUTHOR [+2]

Abstract

Confocal scanning principles employed in metrology microscopes are applied to control overlay alignment and best focus in photoresist exposure tools used in integrated circuit manufacture.

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Confocal Scanning Optical System for Overlay And Focus Control of Exposure Tools

       Confocal scanning principles employed in metrology
microscopes are applied to control overlay alignment and best focus
in photoresist exposure tools used in integrated circuit manufacture.

      As described in (*), a confocal scanning optical system has a
very narrow depth of focus and light is returned to a detector
primarily from the focal plane.  This system is incorporated in a
photoresist exposure tool to detect and drive control of 1) distance
of exposure lens to a photoresist plane (Z positioning) and 2) planar
position of a mask image with respect to alignment marks on a
semiconductor wafer created in an earlier photo processing step (X
and Y positioning).

      Because of the narrow depth of focus of the confocal system, Z
positioning to place the focal plane of the mask image in the
photoresist plane is performed with a high degree of accuracy.

      Because the light reaching the detector is nearly all from the
plane to which the confocal system is focused, an alignment mark
which is buried under a layer or two of semi-transparent material is
still detectable.  This feature is especially important when
processing includes a planarizing step before applying photoresist,
thereby eliminating top surface topography created by a buried
alignment mark as an aid for alignment.  During X and Y positioning,
the confocal system may be focused on the plane of the...