Research on automatic detection method for surface defects of large-size gratings

In this paper, a grating defect detection system based on the principle of darkfield imaging is proposed for the surface defect detection of existing large-size gratings, and the corresponding mechanical device is built. The device mainly includes two categories: hardware system and software system, of which the hardware system has lighting module, image acquisition and displacement module, and the software system has target edge reconstruction module and target edge detection module. Through the device, the surface defects of two-dimensional diffraction gratings of different sizes and different process conditions (substrate, mask grating, etching grating and coating grating) are automatically detected, and the statistical data of different types of defects are given. Through the analysis and study of the cause, transmittance and how to avoid different kinds of grating defects, whether it will affect the optical performance of grating use.The experimental results show that the proposed system meets the needs of large-size grating surface defect detection and evaluation in terms of accuracy and accuracy of defect detection, and the mechanical structure of the device is simple and compact, which has the potential of industrial large-scale detection. The device is of great significance for evaluating large-size high-precision grating manufacturing technology.