Research On Surface Defects Detection Method Based On Microscopic Phase Measuring Deflectometry

With the development of science and technology,optoelectronic information industry has developed rapidly.Microelectronics and micro devices are used in various fields of people’s production and life,so there is an urgent need for the detection and control of micro surface defects.Compared with confocal microscope or white light interferometer,structured light detection technology has the advantages of low cost and easy industrialization,so it develops rapidly and occupies an important position in industrial surface detection.After people found the advantages of structured light technology,they gradually applied the micro fringe projection technology and micro phase measuring deflectometry to the detection for micro defects.This paper starts with the detection of defects by microscopic phase measurement(PMD),and then conducts research on optical path simulation optimization and defect detection methods.The specific research content is as follows:In theoretical analysis,a simple model of surface defects of reflective elements is established,and the scattering characteristics of surface defects are introduced.The principle and characteristics of micro PMD detection and modulation are analyzed and studied.The phase unwrapping algorithm based on sorting of modulation and the principle of super-resolution by structured light microscopy are described.Compared with the macro phase measuring deflectometry system,the micro PMD system adopts coaxial illumination structure,and introduces optical elements such as objective lens and splitter.Therefore,in order to improve the imaging quality and the accuracy of subsequent surface defect detection,the ZEMAX simulation is used to adjust the distance between optical elements.Comparing the simulation results of the initial structure with the optimized results,the optimized results reduce the RMS radius by 2.73 times,the MTF value of the central field of view increases by 3 times,the MTF value of the sagittal direction of the edge field of view increases by nearly two times,the wavefront aberration decreases by 3.15 times,and the distortion and imaging blur are reduced.According to the aberration theory,the aberration of the optical system can be analyzed and studied,which can provide further guidance for the subsequent optimization.Based on the theory of micro PMD,the distance δ between the projected aerial fringes and the surface of the object to be measured will affect the contrast of the fringes,and then affect the modulation.Therefore,this paper proposes a micro structured light modulation analysis technology for defect detection.Then,through simulation and experiment,the effectiveness of MSMAT for defect detection is verified.For the phase unwrapping method,an explicit phase unwrapping method is proposed,and its effectiveness is verified by simulation and MSMAT experiments.For super-resolution imaging,multi-step phase shifting experiment is carried out by MSMAT.The experimental and simulation results show that multi-step phase shifting can improve the quality of modulation results,and verify that the spectrum of modulation results is wider than that of traditional white light.According to the experiment of different reflectivity and different defect types,the experimental results verify the ability of MSMAT for defect detection,and discuss the factors that affect the modulation system in the experiment.