Mark image geometric distortion calibration in alignment system for multilevel imprint lithography

A distortion model based on cubic polynomial is established concerning various linear and nonlinear distortions in the alignment system based on video image for multi-level imprint lithography and a calibration technique based on controlled points is adopted to solve the model. By minimizing the error object function, the indeterminate coefficients of the distortion model are obtained. The calibration results are evaluated by the standard deviation of calibration error, and the results show that the fitting error is 0.22 μm. By introducing distortion correction based on this model, the alignment error due to image geometric distortion in the alignment system is reduced from 2.5 μm to 0.25 μm, which meets the requirement of precise positioning of alignment marks.