An investigation of the wetting behavior of heat-treated silicon nitride particles with liquid silicon

Silicon nitride is commonly used as a coating material for the silica crucibles utilized for the growth of multicrystalline silicon by directional solidification. The coating material might introduce impurities into the silicon melt during the growth. To investigate the wetting and incorporation behavior of the silicon nitride particles, silicon nitride particles were put intentionally into silicon rods, which were then grown by the float zone technique. To ensure that the particles stay within the melt and are not pushed out of the molten zone, the particles must show good wetting. Superheating the silicon nitride powders up to 105 K over the melting point of silicon was a successful approach to ensure wetting and thus to investigate the incorporation behavior of the silicon nitride in photovoltaic silicon. The heat treated silicon nitride particles stayed within the melt zone during the float zone experiments and the distribution behavior of the particles could be studied. Incidentally, the results imply that to suppress incorporation of silicon nitride particles (as coating material) into molten silicon during directional solidification, superheating the melt must be avoided