Silica versus silicon nitride crucible: Influence of thermophysical properties on the solidification of multi-crystalline silicon by Bridgman technique

Abstract

In contrast to standard silica crucibles, which can only be used once, crucibles made of silicon nitride have the potential of being used several times for directional solidification of multi-crystalline silicon ingots. In this paper numerical and experimental results on the influence of crucible thermal properties on the solidification of multi-crystalline silicon in a Bridgman furnace are presented. A transient CFD model of the Bridgman furnace has been used for this purpose including all important aspects of heat transfer, e.g. convection, conduction and radiation. Due to the low thermal resistivity of the silicon nitride material more heat is extracted through the crucible bottom, which leads to a prolonged melting time, whereas solidification time is reduced. The prolonged melting time was compensated by replacing the two insulating carbon fibre discs underneath the crucible by alumina fibre material. Finally melting and solidification time is reduced significantly.