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Proceedings Article

Koehler illumination in high-resolution optical metrology

[+] Author Affiliations
Yeung Joon Sohn, Brian M. Barnes, Lowell Howard, Richard M. Silver, Ravikiran Attota, Michael T. Stocker

National Institute of Standards and Technology

Proc. SPIE 6152, Metrology, Inspection, and Process Control for Microlithography XX, 61523S (March 24, 2006); doi:10.1117/12.655126
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From Conference Volume 6152

  • Metrology, Inspection, and Process Control for Microlithography XX
  • Chas N. Archie
  • San Jose, CA | February 19, 2006


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.

© (2006) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

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

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