Numerical Analysis of the Influence of Size Upgrading on Oxygen and Carbon Impurities in Casting Silicon

Size upgrading is the main method to increase production capacity and reduce production costs during the directional solidification of silicon ingots. The performance of solar cells depends directly on the quality of the wafer and impurities distributions in silicon ingots. The distributions of oxygen and carbon impurities in G6 and G7 directional solidification furnaces are studied. The transient global simulation method is used to calculate the coupled thermal and flow fields in the furnaces, considering the convection of gas and melt, chemical reactions, and segregations of the impurities at the crystal-melt interface. The simulation results show that the distributions of oxygen and carbon impurities change significantly in the silicon ingot at different growth stages, especially the position of the highest concentration of carbon impurities has shifted. Compared with the G6 furnace, the average concentrations of oxygen and carbon in silicon crystal in the G7 furnace are reduced by 6.7%, and 7.3% respectively. With the growth of silicon crystal, the average concentration of oxygen gradually decreases, while the average concentration of carbon gradually increases.