Pre-compensation method for suppressing pattern placement error of computer-generated holograms in laser direct writing lithography

Computer-generated hologram (CGH) is currently one of the most accurate measurement techniques widely used in optical surface testing. A critical factor encing the measurement accuracy is pattern placement error (PPE) of CGH, which could be theoretically suppressed through calibration and compensation measurement results. However, since the compensation is performed after CGH fabrication, the inherent pattern error will inevitably limit accuracy improvement. this study, to fundamentally improve the placement accuracy of CGH pattern, a pre-compensation method for suppressing the placement error during cartesian direct writing was proposed. Firstly, the placement error of the two-dimensional guide rails in laser direct writing lithography system is measured through a calibration method. Secondly, the low-frequency error component of the measured placement error is extracted, and pre-compensated as systematic errors in CGH pattern. Finally, a modified CGH pattern was exposed and tested to demonstrate the effectiveness of the developed pre-compensation method. With implementation of pre-compensation, PPE of the CGH pattern is reduced by 65%, and the CGH wavefront accuracy is improved by 55%.