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Applied Optics

Applied Optics


  • Editor: James C. Wyant
  • Vol. 47, Iss. 4 — Feb. 1, 2008
  • pp: 495–503

Linewidth measurement technique using through-focus optical images

Ravikiran Attota, Richard Silver, and Ronald Dixson  »View Author Affiliations

Applied Optics, Vol. 47, Issue 4, pp. 495-503 (2008)

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We present a detailed experimental study of a new through-focus technique to measure critical dimension linewidth with nanometer sensitivity using a bright field optical microscope. This method relies on analyzing intensity gradients in optical images at different focus positions, here defined as the focus metric (FM) signature. The contrast of an optical image of a structured target, where a particular structure is repeated several times, varies greatly as it is moved through-focus if the spacing between the structures is such that the scattered field from the features interferes. Complex, distinguishable through-focus optical response occurs under this condition giving rise to the formation of several cyclic high and low contrast images. As a result it exhibits several FM signature peaks as opposed to a single FM peak for structures nearly isolated. This complex optical behavior is very sensitive to the dimensions of the target geometry. By appropriately analyzing the through-focus optical image, information can be obtained regarding the target. An array of lines is used as a structured target. Linewidth measurements were made by using experimental through-focus optical data obtained using a bright field microscope and simulated optical data. The optical results are compared with reference metrology tools such as a critical dimension atomic force microscope and critical dimension scanning electron microscope.

© 2008 Optical Society of America

OCIS Codes
(110.6760) Imaging systems : Talbot and self-imaging effects
(120.3940) Instrumentation, measurement, and metrology : Metrology
(180.6900) Microscopy : Three-dimensional microscopy
(290.3700) Scattering : Linewidth
(350.2770) Other areas of optics : Gratings

ToC Category:
Instrumentation, Measurement, and Metrology

Original Manuscript: July 2, 2007
Revised Manuscript: December 10, 2007
Manuscript Accepted: December 11, 2007
Published: January 23, 2008

Ravikiran Attota, Richard Silver, and Ronald Dixson, "Linewidth measurement technique using through-focus optical images," Appl. Opt. 47, 495-503 (2008)

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