Online monitoring for Si solar cell manufacturing

We have developed an online monitoring system that can image various parameters of wafers and cells as they are transported over a conveyer belt. For silicon applications, these parameters include: sawing irregularities, texture quality and uniformity, AR coating thickness, metallization statistics on finger and busbar widths, and final “visual inspection.” For a multicrystalline wafer, it also measures grain size and grain orientations. The system involves a light source and a line camera, to record the reflectance image of the wafer/cell moving at speeds up to 5 inches per second (ips). A high-speed computer then transforms the reflectance images into the appropriate parameter images. We will describe the essential principles of the system, image processing methods, and discuss examples of the applications in a manufacturing facility. The current system is a single wafer line, carrying wafers/cells at a speed of 2 inches per second. The imaging system can be adapted to existing conveyor belt assembly.