On the detachment of Si ingots from SiO2 crucibles

Abstract

In a directional solidification furnace, ingots of silicon are contained in a silica crucible covered with a silicon nitride (Si3N4) powder layer. During the crystallization of the ingot, the layer may suffer various behaviors. When properly applied, it can efficiently act as a mechanical shunt between the Si and the silica wall. However, filling of the crucible with silicon pieces can also scratch locally the layer, resulting in deleterious adhesion between ingot and crucible. The layer can also be too thin, or insufficiently pyrolyzed, so that the Si interacts with the silica crucible.An extended simulation is carried out; taking into account the thermo-elastic stresses induced by the difference in thermal expansion coefficients of the crucible and ingot materials that are attached on small areas. The model compares the remaining elastic energy to the adhesion energy between the silicon and the crucible, in order to predict the temperature at which the Si detaches from the crucible in case of sticking. Two configurations are compared in terms of amount of stresses and extent of the ingot volume likely to be impacted by dislocation generation.