Micro crack detection of multi-crystalline silicon solar wafer using machine vision techniques

摘要

Purpose - The detection of invisible micro cracks (μcracks) in multi-crystalline silicon (mc-si) solar wafers is difficult because of the wafers' heterogeneously textured backgrounds. The difficulty is twofold. First, invisible μcracks must be visualized to imaging devices. Second, an image processing sequence capable of extracting μcracks from the captured images must be developed. The purpose of this paper is to reveal invisible μcracks that lie beneath the surface of mc-si solar wafers. Design/methodology/approach - To solve the problems, the authors first set up a near infrared (NIR) imaging system to capture images of interior μcracks. After being able to see the invisible μcracks, a region-growing flaw detection algorithm was then developed to extract μcracks from the captured images. Findings - The experimental results showed that the proposed μcracks inspection system is effective in detecting μcracks. In addition, the system can also be used for the inspection of silicon solar wafers for stain, pinhole, inclusion and macro cracks. The overall accuracy of the defect detection system is 99.85 percent. Research limitations/implications - At present, the developed prototype system can detect μcrack down to 13.4mm. The inspection resolution is high but the speed is low. However, the limitation on inspection speed can easily be lifted by choosing a higher resolution NIR camera. Practical implications - Generally, this paper is a great reference for researchers who are interested in developing automatic optical inspection systems for inspecting solar wafer for invisible μcracks. Originality/value - The research described in this paper makes a step toward developing an effective while low-cost approach for revealing invisible μcrack of mc-si solar wafers. The advantages provided by the proposed system include excellent crack detection sensitivity, capability of detecting hidden subsurface μcracks, and low cost.