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Applied Optics

Applied Optics


  • Editor: James C. Wyant
  • Vol. 46, Iss. 17 — Jun. 10, 2007
  • pp: 3485–3492

Aberration evaluation of alignment optics in lithographic tools by use of a step-height structure highly sensitive to the asymmetry of an optical image

Hideki Ina and Mitsuo Takeda  »View Author Affiliations

Applied Optics, Vol. 46, Issue 17, pp. 3485-3492 (2007)

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To satisfy the increasing demand for extremely tight overlay accuracy in semiconductor manufacturing processes, all the measurement error factors in alignment systems and overlay measurement tools need be identified and eliminated. The principle of most alignment systems is based on image processing of target marks on the wafer under bright-field illumination. Although the phenomenon that the sensitivity to the alignment error varies with the step height (SH) of the mark has been known and used for evaluating the performance of the alignment optics, no investigation has been made into the origin and the physical mechanism of the phenomenon. We propose a simplified optical model that can account for the origin of the asymmetric image and clarify its relation to the SHs. The model is validated with simulation and experimental results. The improved performance of an alignment system using marks with optimally designed SHs is demonstrated.

© 2007 Optical Society of America

OCIS Codes
(110.3960) Imaging systems : Microlithography
(110.5220) Imaging systems : Photolithography
(120.3930) Instrumentation, measurement, and metrology : Metrological instrumentation
(120.3940) Instrumentation, measurement, and metrology : Metrology

ToC Category:
Instrumentation, Measurement, and Metrology

Original Manuscript: October 11, 2006
Revised Manuscript: January 5, 2007
Manuscript Accepted: February 4, 2007
Published: May 18, 2007

Hideki Ina and Mitsuo Takeda, "Aberration evaluation of alignment optics in lithographic tools by use of a step-height structure highly sensitive to the asymmetry of an optical image," Appl. Opt. 46, 3485-3492 (2007)

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  1. See http://public.itrs.net/.
  2. D. J. Coleman, P. J. Larson, A. D. Lapata, W. A. Muth, and A. Starikov, "On the accuracy of overlay measurements: tool and mark asymmetry effects," Proc. SPIE 1261, 139-161 (1990).
  3. T. Kanda, K. Mishima, E. Murakami, and H. Ina, "Alignment sensor corrections for tool induced shift (TIS)," Proc. SPIE 3051, 846-855 (1997).
  4. H. Ina, K. Sentoku, T. Matsumoto, H. Sumitani, and M. Suita, "Alignment mark optimization to reduce tool- and wafer-induced shift for XPA-1000," Jpn. J. Appl. Phys. 38, 7065-7070 (1999). [CrossRef]

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