US Patent 7456473 MOS field effect transistor and manufacture method thereof

A method of manufacturing an MOS field effect transistor, which achieves a faster operation and lower power consumption by using a thin film SOI structure, is provided. The method of manufacturing an MOS field effect transistor to be formed on a semiconductor substrate having a channel layer on a buried oxide film, comprises the steps of forming: a gate electrode on the semiconductor substrate via a gate oxide film; forming a first sidewall which covers a side wall of the gate electrode; forming a box oxide film by etching the buried oxide film; and forming a second sidewall which covers a side wall of the box oxide film in such a way that the second sidewall extends downward along the side wall of the box oxide film.