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Proceedings Paper

A new illumination technique for grating-based nanometer measurement applications
Author(s): Li Jiang
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Paper Abstract

Optical gratings are becoming available with precision down to the 2 nm level, or below. Such gratings can be employed to make highly accurate measuring tools such as optical encoders and coordinate measuring tools which can find numerous applications in integrated circuit industry and elsewhere. Such tools are significantly less expensive than interferometers because of relaxed mechanical tolerances required on the associated stages. However, the accuracy of grating-based measurement tools is limited by optical imaging techniques for viewing the gratings. In this paper, a novel illumination technique involving two parallel coherent beams is developed for grating-based measurement tools with nanometer accuracy. The interference grating image was viewed under a microscope and the video image of the grating was taken and processed. The location of the grating was determined with an error of 0.09 nm. The interference artifacts generally present in laser illumination are eliminated under this new illumination technique. This provides a cleaner starting point for data analysis and thus higher accuracy measurement. The techniques developed here provide levels of accuracy limited only by the errors in the grating. This is comparable to accuracy of state of the art interferometers, but at much lower cost.

Paper Details

Date Published: 23 March 2009
PDF: 9 pages
Proc. SPIE 7272, Metrology, Inspection, and Process Control for Microlithography XXIII, 72723U (23 March 2009); doi: 10.1117/12.813543
Show Author Affiliations
Li Jiang, Tuskegee Univ. (United States)

Published in SPIE Proceedings Vol. 7272:
Metrology, Inspection, and Process Control for Microlithography XXIII
John A. Allgair; Christopher J. Raymond, Editor(s)

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