MANUFACTURE OF SEMICONDUCTOR DEVICE

PURPOSE:To obtain an oxidation resisting mask by forming the surface of a substrate into an oxide film in an oxidizing atmosphere, replacing the atmosphere with a nitriding atmosphere and improving the surface layer of the oxide film into a nitride film. CONSTITUTION:The silicon substrate 1 is thermally oxidized in the acidic atmosphere to form the silicon oxide film 2, the acidic atmosphere is replaced with the nitriding atmosphere, the surface layer of the silicon oxide film 2 is improved to the silicon nitride film 3, and the silicon nitride film 3 and the silicon oxide film 2 of a section functioning as an inactive region 4 are removed using a photo-resist as a mask. A field oxide film 5 burying in the silicon substrate 1 is shaped selectively to the inactive region 4 while employing the silicon nitride film 3 as an oxidation resisting mask through thermal oxidation in the oxidizing atmosphere, the silicon nitride film 3 and the silicon oxide film 2 are removed, an active region 6 is formed, and a gate insulating film 7, a gate electrode 8 and a source-drain region 9 are shaped to said region.