Influence of thermal conductivity and emissivity of heat shield surface material on the thermal field of Czochralski silicon crystal growth

Silicon crystal for solar cells are mainly produced by the Czochralski (CZ) method, in which the quality and production cost of silicon crystal are mainly affected by the thermal field of the crystal growth furnace. While the thermal field is significantly influenced by the heat shield material, in this study, the effect of thermal conductivity and emissivity of the heat shield material on the global thermal field was investigated by numerical simulation in Ansys Fluent software. The heat shield surface is divided into two parts, the high-temperature side part (close to the crucible and melt) and the low-temperature side part (close to the crystal), which are named as Hot-Side-Material and Cold-Side-Material, respectively. The results show that the same material can be chosen for both parts and the smaller the thermal conductivity and the emissivity of the material, the better the thermal field. As the thermal conductivity and emissivity of the heat shield surface material decrease, the melt-crystal (m-c) interface deflection decreases; the maximum thermal stress of the crystal and the required heater power are also reduced, while the crystal axial temperature gradient increases. Therefore, it is recommended to select material with low emissivity and low thermal conductivity as heat shield surface material.