Köhler illumination for high-resolution optical metrology

Yeung Joon Sohn; Brian M. Barnes; Lowell Howard; Richard M. Silver; Ravikiran Attota; Michael T. Stocker

doi:10.1117/12.655126

24 March 2006 Köhler illumination for high-resolution optical metrology

Yeung Joon Sohn, Brian M. Barnes, Lowell Howard, Richard M. Silver, Ravikiran Attota, Michael T. Stocker

Proceedings Volume 6152, Metrology, Inspection, and Process Control for Microlithography XX; 61523S (2006) https://doi.org/10.1117/12.655126
Event: SPIE 31st International Symposium on Advanced Lithography, 2006, San Jose, California, United States

Abstract

Accurate preparation of illumination is critical for high-resolution optical metrology applications such as linewidth and overlay measurements. To improve the detailed evaluation and alignment of the illumination optics, we have separated Koehler illumination into three components. The three Koehler illumination components are defined as full field spatial intensity variation (Koehler factor 1), angular intensity homogeneity (Koehler factor 2), and wavefront phase/intensity homogeneity (Koehler factor 3). We have also proposed a field aperture pattern transfer method to analyze the illumination properties with respect to systematic variations, such as the shape of the source, the intensity distribution at the back focal plane, and the displacements of elements along and off the optical axis. These factors were investigated in both ideal and practical illumination systems. In particular, any angular asymmetry in the illumination proves to have a detrimental effect upon the distribution of light that illuminates the target. Wavefront asymmetry is also studied in the context of an optical system with a coherent or partially coherent light source.

Citation Download Citation

Yeung Joon Sohn, Brian M. Barnes, Lowell Howard, Richard M. Silver, Ravikiran Attota, and Michael T. Stocker "Köhler illumination for high-resolution optical metrology", Proc. SPIE 6152, Metrology, Inspection, and Process Control for Microlithography XX, 61523S (24 March 2006); https://doi.org/10.1117/12.655126

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