Design of a long working distance, large aperture microscope objective for semiconductor precision inspection

In order to solve the problem of the short working distance of the microscope objective in a large aperture, this paper designs a 50× microscope objective with a numerical aperture of 0.75 and a long working distance of 6.2 mm. The objective achieves flat-field and apochromatic for the wavelength range from 436 to 656 nm and maintains high focusing quality in both femtosecond laser (770-790 nm) and YAG laser (1059-1069 nm) ranges. The performance evaluations of the objective show that the resolution reaches 2200 lp/mm, and the modulation transfer function (MTF) indicates that the image quality is close to the diffraction limit within the working ranges. The tolerance analysis reveals that the design meets the requirements for mass production. This paper provides a solution for semiconductor defect detection by combining high resolution with a large working distance.