Effect of crucible cover material on impurities of multicrystalline silicon in a unidirectional solidification furnace

It has been suggested that the use of a crucible cover can reduce the carbon impurity of multicrystalline silicon in a unidirectional solidification furnace. The material of the cover has an obvious effect on the impurity concentration. If the cover is made from an inertia material, such as tungsten or molybdenum, the carbon impurity in multicrystalline silicon can be reduced by 1000 times compared to that in the conventional furnace; however, due to the costliness of tungsten, a cheaper material such as carbon is preferred. When a cover made from carbon is used, the carbon impurity in multicrystalline silicon can be reduced by 10 times compared to that in the conventional furnace. Therefore, an effective and economical method for reducing the carbon impurity is to design a cover made from carbon and with a thin layer of tungsten deposited on the surface.