NOVELTY - The method involves forming a body by kneading a ceramic powder comprising a silicon nitride powder and a binder solution. Slurry is formed by adding another binder solution to the body by adjusting the viscosity of the slurry by adding the latter binder solution or a solvent to the slurry. A release layer (2) is formed by attaching the slurry to a surface of a mold base (20). The ceramic powder is obtained by mixing the silicon nitride powder with a silicon dioxide powder. The mold base is heated before forming the release layer.    USE - Method for forming a mold for manufacturing a silicon ingot for providing a substrate i.e. polycrystalline silicon substrate, for a p-conductivity type solar cell element (all claimed).    ADVANTAGE - The ceramic powder can contain the silicon dioxide powder in addition to the silicon nitride powder, which increases adhesion between the silicon nitride powder particles in the same manner as that of the surface-oxidized silicon nitride powder, thus increasing the strength of the release layer, and reducing the detachment of part of the release layer and the entry of the release layer into a silicon melt during the production of a silicon ingot. The number of revolutions of the kneading mixer in the pellet formation step can be increased compared to the powder mixing step, so that the ceramic powder is brought into contact with the binder solution more frequently, and hence the particles agglomerate quickly and the pellets are efficiently formed, which improves productivity. The addition of the binder solution can reduce the rise of the ceramic powder. The slurry that has been applied by spraying is dried using heating unit arranged inside the mold base when the release layer is formed on the inner surface of the mold base, thus improving the uniformity of dried state. The heating unit has an inverted pyramid-shaped structure and includes four heaters at positions corresponding to four oblique sides, so that the slurry can be sufficiently dried even at inner ends of the mold, where drying is not easily proceed. The contact between the silicon melt and the mold and the entry of impurities into the silicon melt during the manufacturing of the silicon ingot can be reduced, so that the substrate for solar cell elements that can produce a solar cell element in which the degradation of characteristics are reduced can be obtained at a high yield.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are also included for the following:    (1) a method for manufacturing a substrate for a solar cell element    (2) a mold for manufacturing a silicon ingot.    DESCRIPTION OF DRAWING(S) - The drawing shows a perspective view of a mold.    Mold (1)    Release layer (2)    Mold base (20)