Patent ID: 7172942

Claim:
A method for manufacturing a semiconductor elemental device wherein a first gate oxide film and a second gate oxide film thicker than the first gate oxide film are formed on a substrate provided with a device forming region comprised of silicon, comprising the steps of: implanting an element for promoting a forming speed of said each gate oxide film into a region for forming the second gate oxide film of the substrate; and simultaneously forming the first gate oxide film and the second gate oxide film by a thermal oxidation method, wherein in said element implanting step, the element is implanted in space of a depth equal to half the thickness of the second gate oxide film placed in predetermination of its formation from the surface of the substrate in such a manner that with the peak of a concentration distribution of the element as the center, a concentration distribution in which both sides of the peak is given twice as large as a standard deviation of the concentration distribution, is taken.