Global simulation of coupled oxygen and carbon transport in an industrial directional solidification furnace for crystalline silicon ingots: Effect of crucible cover coating

For accurate prediction of oxygen (O) and carbon (C) distributions in the crystalline silicon ingots grown by the industrial directional solidification (DS) furnace, we first performed transient global simulations of heat transfer based on a fully coupled calculation of the thermal and flow fields. The phase change problem was handled by an enthalpy formulation technique based on a fixed-grid methodology. The coupled C and O transport in the DS furnace was then carried out, taking into account five chemical reactions. Special attention was devoted to modeling the O and C impurity segregation during the entire solidification process. It was found that the developed model can successfully simulate the impurity segregation at the growth interface and the obtained boundary layer thickness is similar to that estimated by analytical calculation. The effect of the crucible cover coating on the coupled O and C transport was investigated. The numerical results show that the C concentration in the grown silicon ingot can be reduced by about 60% if the pure graphite cover was replaced by a graphite cover with an inert material coating on it. However, the cover coating did not significantly affect the O concentration in the grown ingot. The numerical predictions of the C concentration showed satisfactory agreement with the experimental measurements.