Subsequently, a film forming step is performed in which an amorphous silicon film 502 is formed in the recess 501A by supplying a silicon source gas to the substrate (see FIG. 1B). In an embodiment, by a chemical vapor deposition (CVD) method, for example, the silicon source gas is supplied in a state in which the substrate is heated so that the amorphous silicon film 502 is formed in the recess 501A. The film thickness of the amorphous silicon film 502 may be set such that, for example, the amorphous silicon film 502 is formed on a bottom surface 501b and a side wall 501s of the recess 501A and the opening in the upper portion of the recess 501A is not blocked by the amorphous silicon film 502. The silicon source gas is preferably a mixed gas of a halogen-containing silicon gas and a hydrogenated silane gas from the viewpoint that it is possible to form a film having an excellent step coverage and low surface roughness. The flow rate of the hydrogenated silane gas is preferably higher than the flow rate of the halogen-containing silicon gas. In this manner, it is possible to reduce the etching property of the silicon film by the halogen originating from the halogen-containing silicon gas, and to form the amorphous silicon film 502 at a high speed. The halogen-containing silicon gas may be, for example, a fluorine-containing silicon gas such as SiF₄, SiHF₃, SiH₂F₂, or SiH₃F, a chlorine-containing silicon gas such as SiCl₄, SiHCl₃, SiH₂Cl₂ (DCS), or SiH₃Cl, or a bromine-containing silicon gas such as SiBr₄, SiHBr₃, SiH₂Br₂, or SiH₃Br. The hydrogenated silane gas may be, for example, SiH₄, Si₂H₆, or Si₃H₈. In addition, before supplying the mixed gas of the halogen-containing silicon gas and the hydrogenated silane gas, a seed layer may be formed by supplying a higher-order silane-based gas or an aminosilane-based gas. By forming the seed layer in the recess 501A, it is possible to reduce the roughness of the amorphous silicon film 502 formed on the seed layer. The higher-order silane-based gas may be, for example, Si₂H₆, S₃H₈, or Si₄H₁₀. The aminosilane-based gas may be, for example, diisopropylamino silane (DIPAS), tri(dimethylamino)silane (3DMAS), or bis(tertiarybutylamino)silane (BTBAS).