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Applied Optics

Applied 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)

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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

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

Chin-Yu Ku, Tan Fu Lei, and Hwang-Kuen Lin, "Focus measurement with a simple pattern design," Appl. Opt. 40, 2662-2669 (2001)

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