An Improved Algorithm to Extract Moiré Fringe Phase for Wafer-Mask Alignment in Nanoimprint Lithography

This paper proposes an improved algorithm based on the phase extraction of the Moiré fringe for wafer-mask alignment in nanoimprint lithography. The algorithm combines the strengths of the two-dimensional fast Fourier transform (2D-FFT) and two-dimensional window Fourier filtering (2D-WFF) to quickly and accurately extract the fundamental frequencies of interest, eliminate noise in the fundamental frequency band by using the threshold of the local spectrum, and effectively suppress spectral leakage by using a Gaussian window with outstanding sidelobe characteristics while overcoming their limitations, such as avoiding the time-consuming parameter adjustment. The phase extraction accuracy determines the misalignment measurement accuracy, and the alignment accuracy is enhanced to the nanometer level, which is 15.8% and 6.6% higher than 2D-FFT and 2D-WFF, respectively. The results of simulations and experiments confirm the feasibility and rationality of the algorithm.