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Comb-referenced frequency-sweeping interferometry for precisely measuring large stepped structures.

Weipeng Zhang, Haoyun Wei, Honglei Yang

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    A new optical interferometry method precisely measures large 3D stepped structures without ambiguity. This technique uses frequency sweeping and Fourier transforms for high accuracy, ideal for microelectronics and MEMS manufacturing.

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    Area of Science:

    • Metrology
    • Optical Engineering
    • Surface Measurement

    Background:

    • Accurate 3D surface measurement is crucial for microelectronics and MEMS.
    • Traditional interferometry methods face limitations with large structures and height ambiguity.
    • Existing techniques often rely on absolute phase values, restricting their non-ambiguity range.

    Purpose of the Study:

    • To propose a precise 3D surface measurement method for large stepped structures.
    • To overcome the height ambiguity inherent in conventional interferometry.
    • To achieve high accuracy and robustness against environmental noise.

    Main Methods:

    • Utilizes optical-frequency-comb-referenced frequency-sweeping interferometry.
    • Employs Fourier-transformed fractional phase retrieval for rapid, single-step analysis.
    • Leverages phase change during frequency sweeping, eliminating reliance on absolute phase.

    Main Results:

    • Achieved precise 3D surface measurement for step heights ranging from 1 μm to 1 mm.
    • Reduced relative uncertainty from tunable laser frequency by three orders of magnitude.
    • Demonstrated standard uncertainty of 45 nm with immunity to noise.

    Conclusions:

    • The proposed method offers unambiguous 3D surface profiling for large structures.
    • It provides a robust and accurate solution for metrology in advanced manufacturing.
    • Enables quality assurance applications in microelectronics and MEMS production.