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Applied Optics

Applied Optics

APPLICATIONS-CENTERED RESEARCH IN OPTICS

  • Vol. 40, Iss. 16 — Jun. 1, 2001
  • pp: 2662–2669

Focus measurement with a simple pattern design

Chin-Yu Ku, Tan Fu Lei, and Hwang-Kuen Lin  »View Author Affiliations


Applied Optics, Vol. 40, Issue 16, pp. 2662-2669 (2001)
http://dx.doi.org/10.1364/AO.40.002662


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Abstract

The increasingly smaller depth of focus of advanced lithographic tools requires that the position of best focus be determined to ensure accuracy and efficiency. We present what we believe is a novel bar in bar that is drawn on a conventional chrome binary mask to translate focal errors into center-to-center shifts of outer and inner bars. An overlay measurement tool can easily measure this shift. A symmetrical center-to-center shift against best focus is created during defocus, and this shift can be well fitted by a second-order polynomial equation. Simply differentiating the fitted equation leads to an accurate and reliable focus value, with a maximum error of less than 0.05 µm. The proposed technique can also be employed to evaluate the tilt, field curvature, and astigmatism of advanced lithographic tools.

© 2001 Optical Society of America

OCIS Codes
(110.3960) Imaging systems : Microlithography
(120.0120) Instrumentation, measurement, and metrology : Instrumentation, measurement, and metrology

History
Original Manuscript: May 9, 2000
Revised Manuscript: February 8, 2001
Published: June 1, 2001

Citation
Chin-Yu Ku, Tan Fu Lei, and Hwang-Kuen Lin, "Focus measurement with a simple pattern design," Appl. Opt. 40, 2662-2669 (2001)
http://www.opticsinfobase.org/ao/abstract.cfm?URI=ao-40-16-2662

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