Flexible calibration and alignment tool for scanning beam interference lithography systems based on aerial imaging

Calibration and alignment of scanning beam interference lithography (SBIL) systems remain major challenges due to the high sensitivity of the interference pattern to multiple system degrees of freedom. In this work, a fringe observation system is presented as a quantitative tool for the calibration and alignment of SBIL writing heads. It consists of a compact microscope mounted on a nanopositioning machine, enabling direct imaging of the aerial writing pattern onto a camera. Fringe motion is quantified using the carrier-frequency method. Based on this approach, a comprehensive calibration protocol was developed to characterize key degrees of freedom, including fringe orientation, fringe period, pattern tilt, and positioning errors during the scan-and-stitch process. The writing pattern was aligned parallel to the scan direction to ensure optimal exposure contrast. The fringe period and pattern tilts were determined with nanometer precision, and scan-and-stitch positioning errors were evaluated along a classical SBIL trajectory. Finally, the effectiveness of the calibration procedure was validated by exposure tests in positive photo resist, demonstrating high structural quality and excellent agreement between structures and optical measurements. The presented fringe observation system provides a powerful tool for SBIL calibration and forms the basis for future implementation of in-situ feedback and compensation strategies to further improve fabrication accuracy.