High-precision wavefront measurement for high numerical aperture microscope objectives based on sub-aperture stitching

Abstract

High numerical aperture (NA) microscope objectives are critical in semiconductor wafer defect inspection. Conventional wavefront measurement approaches are limited by the precision of reference wavefronts and inherent systematic errors, which restricts their performance in high-precision metrology. To address these issues, this paper presents a high-precision wavefront measurement method for high NA microscope objectives based on sub-aperture stitching. A mathematical model of sub-aperture stitching is established, and the Levenberg–Marquardt (LM) iterative algorithm is adopted to accurately solve the nonlinear error coefficients. Furthermore, absolute interferometric measurement techniques are integrated to calibrate the systematic errors of the interferometer and the surface error of the planar mirror. Experimental results on a microscope objective with an NA of 0.9 demonstrate that the proposed method breaks through the aperture and precision limitations of conventional measurement devices, and realizes full aperture wavefront measurement with a PV value of 0.3302 λ and an RMS value of 0.0461 λ. Compared with the traditional full aperture method, the proposed scheme significantly improves both measurement accuracy and spatial resolution. This work provides a reliable technical solution for high-precision wavefront metrology of high NA optical systems.