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Simple and accurate optical height sensor for wafer inspection systems

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Abstract

An accurate method for measuring the wafer surface height is required for wafer inspection systems to adjust the focus of inspection optics quickly and precisely. A method for projecting a laser spot onto the wafer surface obliquely and for detecting its image displacement using a one-dimensional position-sensitive detector is known, and a variety of methods have been proposed for improving the accuracy by compensating the measurement error due to the surface patterns. We have developed a simple and accurate method in which an image of a reticle with eight slits is projected on the wafer surface and its reflected image is detected using an image sensor. The surface height is calculated by averaging the coordinates of the images of the slits in both the two directions in the captured image. Pattern-related measurement error was reduced by applying the coordinates averaging to the multiple-slit-projection method. Accuracy of better than 0.35 μm was achieved for a patterned wafer at the reference height and ±0.1 mm from the reference height in a simple configuration.

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Authors and Affiliations

  1. Process Control Systems Research and Development Department, Hitachi High-Technologies Corporation, Hitachinaka, Ibaraki, 312-8504, Japan

    Kei Shimura & Naoya Nakai

  2. Optical Systems Design Department, Hitachi High-Technologies Corporation, Hitachinaka, Ibaraki, 312-8504, Japan

    Koichi Taniguchi

  3. Graduate School of Pure and Applied Sciences, University of Tsukuba, Tsukuba, Ibaraki, 305-8573, Japan

    Kei Shimura & Masahide Itoh

Authors
  1. Kei Shimura
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  2. Naoya Nakai
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  3. Koichi Taniguchi
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  4. Masahide Itoh
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Correspondence to Kei Shimura.

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Shimura, K., Nakai, N., Taniguchi, K. et al. Simple and accurate optical height sensor for wafer inspection systems. Opt Rev 23, 1–9 (2016). https://doi.org/10.1007/s10043-015-0160-z

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  • DOI: https://doi.org/10.1007/s10043-015-0160-z

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