24 March 2006 Optical critical dimension measurement and illumination analysis using the through-focus focus metric
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Abstract
In this paper we present a unique method of evaluating the angular illumination homogeneity in an optical microscope using the through-focus focus metric. A plot of the sum of the mean square slope throughout an optical image as the target moves through the focus is defined as the through-focus focus metric. Using optical simulations we show that the angular illumination inhomogeneity causes the through-focus focus metric value to proportionately increase at specific focus positions. Based on this observation, we present an experimental method to measure angular illumination homogeneity by evaluating the through-focus focus metric values on a grid across the field of view. Using the same through-focus focus metric, we present a detailed study to measure critical dimensions with nanometer sensitivity with the aid of simulations.
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Ravikiran Attota, Ravikiran Attota, Richard M. Silver, Richard M. Silver, Michael R. Bishop, Michael R. Bishop, Ronald G. Dixson, Ronald G. Dixson, } "Optical critical dimension measurement and illumination analysis using the through-focus focus metric", Proc. SPIE 6152, Metrology, Inspection, and Process Control for Microlithography XX, 61520K (24 March 2006); doi: 10.1117/12.656421; https://doi.org/10.1117/12.656421
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