Measurement and compensation of a stitching error in a DMD-based step-stitching photolithography system.

The step-stitching issue occurring in digital micromirror device (DMD)-based step lithography, which refers to overlapping and misalignment, has dramatically influenced the overall accuracy of the exposed patterns. To address this technical challenge, this paper proposes a testing method to resolve the system tolerance parameters, inclination angle with 0.060±0.003, and magnification with 3.60399±0.00020, which induce the stitching problem. With these two parameters, a compensation strategy on motion is implemented to precisely control the step distance of the stage so that the edge-to-edge stitching error is reduced to about 0.150 µm and the corner-to-corner stitching error is less than 0.500 µm. The changes of the linewidth induced by the displacement error due to the stage control accuracy and illumination nonuniformity caused by the light source are simulated and analyzed, and the image preprocessing method based on a gradual grayscale mask is employed to improve the quality of stitching. Using this method, the linewidth difference is controlled to be within 0.150 µm. After finishing all the corrections and imaging preprocessing, the transverse error has become almost invisible, and the longitudinal error has been reduced by 97.72%. Experimental results demonstrate that the improved stitching accuracy could achieve high-fidelity devices.