Design and experiment of high resolution detection imaging system for ultra-thin and ultra-short object-image distance

In order to shorten the axial and radial dimensions of the 12-inch wafer detection imaging system, a solution combining the small Angle prism refraction path and the ultra-short object-image distance lens is proposed. A small Angle prism with better shape accuracy than 1/12λ (λ=632.8 nm) is designed to convert the optical path and realize the horizontal arrangement between the lighting system and the imaging lens. The radial size is only 80 mm, which greatly reduces the radial size of the whole system without affecting the imaging quality. At the same time, a small angle of 12° bright field lighting is realized. A symmetrical hybrid optical system with magnification of 0.264 is designed. A pure spherical system is used to obtain a large imaging field of view. The image height is 81.92 mm, and the object image distance is only 392.5 mm, which greatly reduces the axial size of the whole system. The design results show that the average optical transfer function of the whole imaging system is better than 0.4@100l p/mm, the relative distortion is better than 0.03%, and the uniformity of the image surface illuminance is better than 50%. The actual test results show that the actual imaging resolution is better than 18.88 μm, which reaches the ultimate resolution of the system. The uniformity of illumination of image surface is 43.3%, which meets the development requirement of uniformity better than 40%. The research results show that the ultra-thin and ultra-short object-image distance imaging system is reasonable and effective, which solves the problem of space size compression of the 12-inch wafer detection imaging system and reduces the development cost. It provides a reference for the development of the imaging system for detecting large objects in short distance. © 2023 Editorial Office of Chinese Optics. All rights reserved.