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Interferometric Measurement System for Overlay Measurement in Lithographic Processes

IP.com Disclosure Number: IPCOM000111455D
Original Publication Date: 1994-Feb-01
Included in the Prior Art Database: 2005-Mar-26
Document File: 2 page(s) / 40K

Publishing Venue

IBM

Related People

Makosch, G: AUTHOR

Abstract

The overlay of various device layers on a silicon wafer is measured interferometrically by the measurement arrangement illustrated in the Figure. In this method special cross-grids serving as overlay marks on the object wafer are employed. The relative displacement of these patterns in x and y directions is monitored by measuring the phase difference between two pairs of diffraction orders simultaneously occurring in x and y directions by illuminating these patterns with a focused laser beam. For sensing the adjacent grid patterns which are consecutively processed on the wafer, the laser spot illuminating the grid is internally displaced by tiltable glass plates controlled by galvanometric scanners.

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Interferometric Measurement System for Overlay Measurement in Lithographic
Processes

      The overlay of various device layers on a silicon wafer is
measured interferometrically by the measurement arrangement
illustrated in the Figure.  In this method special cross-grids
serving as overlay marks on the object wafer are employed.  The
relative displacement of these patterns in x and y directions is
monitored by measuring the phase difference between two pairs of
diffraction orders simultaneously occurring in x and y directions by
illuminating these patterns with a focused laser beam.  For sensing
the adjacent grid patterns which are consecutively processed on the
wafer, the laser spot illuminating the grid is internally displaced
by tiltable glass plates controlled by galvanometric scanners.  The
two pairs of first-order diffraction beams occurring in x and y
directions are recombined by two sets of Wollaston Prisms (W.P.); two
different phase monitors are employed to measure their phase
difference relating to the pattern displacements in both directions.
The measurement precision obtained by this technique is expected in
the subnanometer region.  This method is especially suited for
monitoring latent overlay patterns in resist.