Polycrystalline silicon substrates have been used as one type of a semiconductor substrate for forming solar cell elements. Polycrystalline silicon substrates are obtained by slicing a silicon ingot at a predetermined thickness. When such a silicon ingot is formed, a mold having a release layer formed on the inner surface thereof may be used. The release layer is formed as follows. First, a silicon nitride powder is mixed with an aqueous polyvinyl alcohol solution under stirring to prepare a slurry. The inner surface of a mold base is then coated with the slurry to form a release layer.
During the preparation of the slurry, particles of the silicon nitride powder may easily adhere to one another to form coarse particles (e.g., average diameter: about 100 μm). If a release layer is formed using a slurry having such coarse particles, the release layer may be easily detached from the mold because the bonding strength between the coarse particles is weak. This may require an additional step of pulverizing the coarse particles into small particles.
Thus, the number of steps performed in the formation of a mold used for manufacturing an ingot needs to be decreased.