SEPARATING METHOD OF SEMICONDUCTOR ELEMENT

PURPOSE:To form a separating oxide film selectively and to prevent the yield of bird's beaks, by utilizing the difference in oxidizing speeds, and forming an element-separating thick oxide film in a region other than an active region. CONSTITUTION:A silicon oxide film 2 is formed on the surface of a P type semiconductor substrate 1. With a resist pattern as a mask, a channel stopping layer 4 is formed. Then, ions are implanted, and a polycrystalline silicon film 62 is formed by the heat treatment in a nitrogen atmosphere. The oxidizing speed of the polycrystalline silicon is faster than that of single crystal silicon. Therefore, when tye polycrystalline silicon film 62 is heat-treated in a wet oxygen atmosphere, the silicon film 62 is oxidized by a silicon oxide film 7. Then, the oxide film in an active region is etched, and a gate electrode 9, a source 10 and a drain 11 are formed.