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Proceedings Paper

Illumination optimization for optical semiconductor metrology
Author(s): Bryan M. Barnes; Lowell P. Howard; Richard M. Silver
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Paper Abstract

Uniform sample illumination via Kohler illumination is achieved by establishing a pair of conjugate focal planes; a light source is focused onto the condenser lens back focal plane while the image of the field aperture is focused at the plane of the specimen. Placement accuracy of these elements along the optical axis will determine the quality of the spatial homogeneity of the illumination in the sample plane. Imaging is therefore inherently sensitive to the tolerance of this alignment. Measuring three-dimensional features on semiconductor wafers has demonstrated an additional requirement for angular illumination homogeneity, as this is critical for robust matching between experimental results and numerically modeled results. We outline our techniques for aligning a custom-built microscope that features a 12 mm diameter conjugate back focal plane, beginning with the establishment of an optical axis based upon the objective lens. We then illustrate the techniques used to establish the quantitative degree of spatial and angular homogeneity through quantifying the resultant illumination while apertures are scanned across this conjugate back focal plane. Examples of the correlation between homogeneity and optical metrology are provided.

Paper Details

Date Published: 5 September 2006
PDF: 11 pages
Proc. SPIE 6289, Novel Optical Systems Design and Optimization IX, 62890P (5 September 2006); doi: 10.1117/12.681064
Show Author Affiliations
Bryan M. Barnes, National Institute of Standards and Technology (United States)
Lowell P. Howard, Precera, Inc. (United States)
Richard M. Silver, National Institute of Standards and Technology (United States)

Published in SPIE Proceedings Vol. 6289:
Novel Optical Systems Design and Optimization IX
José M. Sasian; Mary G. Turner, Editor(s)

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