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31 October 2016 Image grating metrology using phase-stepping interferometry in scanning beam interference lithography
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Large-sized gratings are essential optical elements in laser fusion and space astronomy facilities. Scanning beam interference lithography is an effective method to fabricate large-sized gratings. To minimize the nonlinear phase written into the photo-resist, the image grating must be measured to adjust the left and right beams to interfere at their waists. In this paper, we propose a new method to conduct wavefront metrology based on phase-stepping interferometry. Firstly, a transmission grating is used to combine the two beams to form an interferogram which is recorded by a charge coupled device(CCD). Phase steps are introduced by moving the grating with a linear stage monitored by a laser interferometer. A series of interferograms are recorded as the displacement is measured by the laser interferometer. Secondly, to eliminate the tilt and piston error during the phase stepping, the iterative least square phase shift method is implemented to obtain the wrapped phase. Thirdly, we use the discrete cosine transform least square method to unwrap the phase map. Experiment results indicate that the measured wavefront has a nonlinear phase around 0.05 λ@404.7nm. Finally, as the image grating is acquired, we simulate the print-error written into the photo-resist.
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Minkang Li, Changhe Zhou, Chunlong Wei, Wei Jia, Yancong Lu, Changcheng Xiang, and XianSong Xiang "Image grating metrology using phase-stepping interferometry in scanning beam interference lithography", Proc. SPIE 10022, Holography, Diffractive Optics, and Applications VII, 1002212 (31 October 2016);

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