Browse Prior Art Database

Optimum Overlay

IP.com Disclosure Number: IPCOM000111494D
Original Publication Date: 1994-Feb-01
Included in the Prior Art Database: 2005-Mar-26
Document File: 2 page(s) / 53K

Publishing Venue

IBM

Related People

Wagner, D: AUTHOR

Abstract

The yield in semiconductor manufacturing can be improved if the overlay measurements can be made more precise. The overlay measurement systems on the market are white light microscopes with TV evaluation. For more than 15 years they have been in use. The performance of these systems has reached a summit with a standard deviation of 3 &sigma. = 12 nm. This is good for the 64 Mbit chip, but for future generations a new measurement principle seems necessary. The main error sources in overlay measurements are the roughness of the pattern and the signal-to-noise ratio of the TV camera. Both errors should be made distinctly smaller.

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Optimum Overlay

      The yield in semiconductor manufacturing can be improved if the
overlay measurements can be made more precise.  The overlay
measurement systems on the market are white light microscopes with TV
evaluation.  For more than 15 years they have been in use.  The
performance of these systems has reached a summit with a standard
deviation of 3 &sigma.  = 12 nm.  This is good for the 64 Mbit chip,
but for future generations a new measurement principle seems
necessary.  The main error sources in overlay measurements are the
roughness of the pattern and the signal-to-noise ratio of the TV
camera.  Both errors should be made distinctly smaller.

      It is proposed to use a laser-scanning microscope for future
overlay measurements, because such a system is more flexible for
improvements.  In the laser-scanning microscope a diffraction limited
light spot scans the surface of the object.  The power of the laser
defines the signal to noise.  With small lasers (&tilde.  5 m W) a
signal-to-noise ratio of more than 200 has been measured.  The
signal-to-noise ratio of a TV camera is typically &tilde 20.

      Overlay measurements with the laser scanner should be further
improved by using a light spot which has a rectangular shape.  Only
in the scan direction is the highest possible resolution used.  This
has the advantage that we are averaging over a long part of the rough
edge and have the best measurement resolution in the scan direction.
T...