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Proceedings Paper

Impact Of Wafer Flatness On Submicron Optical Lithography
Author(s): Ling Liauw; Andrew Muray; Mung Chen
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Paper Abstract

Local wafer thickness variation is a significant source of defocus error for submicron lithography. A method of characterizing the flatness of wafers using the auto-focus system of a stepper is developed. An analysis of the data is carried out by a program that provides the distributions of TTV (total thickness variation), LTV (local thickness variation) and LAV (local averaged thickness variation). Contour mapping of the average height per field across a wafer can reveal the areas where the most or least rapid thickness changes are occurring, which can be caused by vacuum bending, chuck tilt, or the different polishing techniques used by vendors. The areas of investigation include a comparison of samples supplied by several silicon vendors, the effects of edge exclusion, and the impact of typical MOS process steps. Wafer flatness is correlated to critical dimension control. In the worst case, local thickness variation within a typical stepper field of more than four microns is observed on new, silicon wafers which causes resist bridging over a large portion of an image field. Finally, the potential benefit of wafer leveling systems is discussed.

Paper Details

Date Published: 1 January 1987
PDF: 7 pages
Proc. SPIE 0772, Optical Microlithography VI, (1 January 1987); doi: 10.1117/12.967055
Show Author Affiliations
Ling Liauw, Intel Corporation (United States)
Andrew Muray, Sentry Schlumberger (United States)
Mung Chen, Intel Corporation (United States)

Published in SPIE Proceedings Vol. 0772:
Optical Microlithography VI
Harry L. Stover, Editor(s)

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