High-Sensitivity Interferometric Schemes for ML2 Micromirror Calibrations

摘要

This paper presents an interferometric method with high sensitivity and good linearity for calibration of micromirror arrays used in maskless lithography. An analytic model based on electric-field perturbation is developed to quantify the influences of mirror configuration and defocus on calibration sensitivity. With the analytic model, two optimization strategies to achieve the highest sensitivity are developed. For a 5-by-5 sub-array with a pixel size of 0.5λ/NA, the sensitivity is improved from 0.0078 I/° when the surrounding pixels are not actuated, to 0.02286 I/° and 0.0347 I/° when the pixels are arranged in optimized schemes at defocus of 0.0RU and 1.5RU, respectively. The typical improvement is about 3X to 4X when the optimized calibration schemes are used.