High-Precision Phase Extraction and Error Analysis of Ronchi Lateral Shearing Interferometry

Double-grating Ronchi lateral shearing interferometry is a primary method for measuring wavefront aberration at the exit pupil of a lithographic projection lens. It has the advantages of being reference-free, having a common path, and having a simple structure that can be easily integrated. This method is suitable for in-situ measurement of wavefront aberration in lithographic projection lens. Phase extraction is a crucial step in this method, as it directly affects the accuracy of the final wavefront aberration measurement. To suppress the interference of high diffraction orders in double-grating Ronchi shearing interferometry, a high-precision shear phase extraction algorithm is proposed. This algorithm can eliminate all high diffraction orders in the overlapping area between ±1st orders, thereby improving the accuracy of the shear phase extraction. The simulation results show that only high-frequency residuals exist in the shear phase extraction errors and are almost negligible, which indicates that the proposed algorithm can effectively eliminate all high diffraction orders theoretically. The experiment is carried out on double-grating Ronchi shearing interferometry system with a shear ratio of 0.058, and compared with the measurement result of dual-fiber point diffraction interferometer, both of the results have the same wavefront aberration distribution, which further verifies the effectiveness of the shear phase extraction algorithm.