A thermodynamic model for the formation of bubble defects in multicrystalline silicon ingot

Abstract

Preparation of multicrystalline silicon for solar cells is significant to photovoltaic industry. Up to now, the formation of bubble defects during directional solidification of multicrystalline silicon has not been explored clearly. In the present experiment, spherical bubble defects distributed randomly at ingot top, and the surface of bubble defects was covered with SiC or Si3N4 particle. A thermodynamic model was proposed to illustrate the formation of bubble defects. Bubble defects were caused by gaseous SiO in silicon melt. SiO was the reaction product of melt silicon and oxygen. Oxygen was dissolved by quartz crucible, diffusing through broken Si3N4 coatings into silicon melt. Gaseous SiO in the silicon melt nucleated and grew into bubbles against insoluble particles, such as SiC and Si3N4, and finally enveloped in solid silicon, producing bubble defects. According to the principle of thermodynamics, the formation process was discussed in detail.