Ingot pulling with electron beam heating: Process enhancements

PV cells efficiency increase by employing FZ silicon was shown in a series of works. At PVSC40 we reported our results in development of cheap FZ feedstock production using electron beam heating. However, we have encountered difficulties with obtaining dislocation free FZ single crystals from our rods and rods diameter had substantial fluctuations. Source of generation of previously absent dislocations was determined and eliminated. Dislocation free single crystals have been grown from bottom parts of newly pulled rods. Process image analysis peculiarities during automation development are discussed. Devised image processing techniques shall enhance PID regulation, rods with acceptable diameter fluctuation are pulled.