PURPOSE: To form a polycrystalline silicon film having a flat surface shape by a method wherein an amorphous silicon layer is formed on a substrate, an oxide film is formed on its surface and the substrate is heated and made polycrystalline.

CONSTITUTION: A 4-inch n-type silicon (001) substrate where a silicon oxide film 11 having a thickness of 2000 has been formed on the surface by a thermal oxidation operation is used as a specimen wafer. A silicon molecular beam at 7A/s is applied from an electron-gun type silicon vapor deposition apparatus while a substrate temperature is set at room temperature; an amorphous silicon layer 12 having a thickness of 2000 is formed on the oxide film 11. In addition, its surface is irradiated with plasma oxygen generated from an electron cyclotron resonance cell; the surface is oxidized; an oxide film 13 is formed. After that, the substrate is heated at 650°C for 10 minutes; polycrystalline silicon 14 is formed.