Enhancing accuracy of alignment measurement in lithography using two-dimensional desirable sidelobe convolution window

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Suppressing spectral leakage is crucial for achieving high-precision measurements using fringe images. However, existing classical windows are not effective in suppressing spectral leakage owing to their inadequate performance, leading to inaccurate measurements. To enhance the accuracy of alignment measurement for lithography by suppressing the spectral leakage associated with phase extraction of Moiré fringes, we introduce a novel two-dimensional desirable sidelobe convolution window (2D-DSCW), constructed using the maximum sidelobe attenuation window as the basis, followed by multiple self-convolutions. The 2D-DSCW with a reasonable order exhibits outstanding sidelobe behaviors, with the peak sidelobe level and sidelobe attenuation rate proportional to the convolution order. Based on this window, an improved windowed fast Fourier transform algorithm is established. Simulation and experimental results reveal that compared with classical windows, the proposed approach can more effectively suppress spectral leakage, enhancing phase extraction accuracy, and thus enabling lithography alignment with an accuracy of sub-1-nm (0.91 nm).