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Optics Express

Optics Express

  • Editor: C. Martijn de Sterke
  • Vol. 16, Iss. 7 — Mar. 31, 2008
  • pp: 4698–4705

Calibration of wafer surface inspection systems using spherical silica nanoparticles

Thomas A. Germer, Christian Wolters, and Don Brayton  »View Author Affiliations

Optics Express, Vol. 16, Issue 7, pp. 4698-4705 (2008)

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Silica nanospheres with diameters ranging from 60 nm to 269 nm are investigated as an alternative to polystyrene spheres for calibrating laser-scattering-based wafer surface inspection systems, since they are less susceptible to changes upon ultraviolet exposure. Polystyrene and silica spheres were classified by differential mobility analysis before being deposited onto bare silicon wafers, and scattered signals were measured by two commercial tools using 488 nm and 355 nm laser light. The instrument signals were modeled by integrating a theoretically-determined differential cross section over the collection geometry of each tool, and the predicted signals were compared to the measured signals. The resulting calibrations, whether performed using the polystyrene spheres, the silica spheres, or both, were found to be equivalent and to meet industry requirements, provided the index of refraction of the silica spheres was allowed to be a floating parameter. The indices were found to be 1.413 and 1.421 at 488 nm and 355 nm, respectively, consistent with a void fraction of 11.4%.

© 2008 Optical Society of America

OCIS Codes
(120.4630) Instrumentation, measurement, and metrology : Optical inspection
(120.4800) Instrumentation, measurement, and metrology : Optical standards and testing
(290.3030) Scattering : Index measurements
(290.5850) Scattering : Scattering, particles

ToC Category:
Instrumentation, Measurement, and Metrology

Original Manuscript: February 11, 2008
Revised Manuscript: March 7, 2008
Manuscript Accepted: March 9, 2008
Published: March 20, 2008

Thomas A. Germer, Christian Wolters, and Don Brayton, "Calibration of wafer surface inspection systems using spherical silica nanoparticles," Opt. Express 16, 4698-4705 (2008)

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  17. Certain commercial equipment, instruments, or materials are identified in this paper in order to specify the experimental procedure adequately. Such identification is not intended to imply recommendation or endorsement by the National Institute of Standards and Technology, nor is it intended to imply that the materials or equipment identified are necessarily the best available for the purpose.
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  20. The uncertainties quoted in this article were obtained by estimating the standard uncertainty u for the measurement and multiplying by a coverage factor of k = 2. These values correspond to a confidence level of 95%.

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