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Proceedings Paper

Size matters in overlay measurement
Author(s): Nigel P. Smith; Brennan L. Peterson; Gary R. Goelzer
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Paper Abstract

We report an analysis of measurements of overlay targets fabricated in a single lithography step in a resist film. With patterns printed in a single step the expected result is zero, providing a rare opportunity to qualify the measurement error completely. Our results allow validation of a complete model for this error, which includes precision and TIS terms that vary as 1/√L, where L is the total pattern length in each target. Removing the precision and TIS effects shows that the remaining errors, which are usually undetectable, also vary as 1/√L. This residual error is very small (0.1nm or less) for the very large targets normally used in scanner qualification, but exceed the ITRS goals for overlay measurement uncertainty in traditional image-based overlay targets smaller than 25x25μm. As the industry drives towards smaller overlay targets it is important to consider the impact on complete measurement uncertainty, and to maximize the information content of each target. We show that acceptable uncertainty in 10x10μm targets is possible using targets patterned with dense gratings that can be measured by both diffraction and imaging tools.

Paper Details

Date Published: 5 April 2012
PDF: 12 pages
Proc. SPIE 8324, Metrology, Inspection, and Process Control for Microlithography XXVI, 832418 (5 April 2012); doi: 10.1117/12.918076
Show Author Affiliations
Nigel P. Smith, Nanometrics Inc. (United States)
Brennan L. Peterson, Nanometrics Inc. (United States)
Gary R. Goelzer, Nanometrics Inc. (United States)

Published in SPIE Proceedings Vol. 8324:
Metrology, Inspection, and Process Control for Microlithography XXVI
Alexander Starikov, Editor(s)

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