| 摘要 |
PROBLEM TO BE SOLVED: To enable the gate insulating films of field-effect transistors of different breakdown voltages to be formed on the same substrate at the same time so as to simplify a process of manufacturing a semiconductor device. SOLUTION: A gate insulating film is formed on the primary surface of a semiconductor substrate 1, and a resist film with an opening is formed thereon, The primary surface of the semiconductor substrate 1 is subjected to an O2 plasma treatment using the resist film as a mask. After the resist film is removed, the substrate 1 is subjected to a cleaning treatment, and the surface of a part of an oxide film irradiated with O2 plasma is etched, so that MOS field-effect transistors provided with gate insulating films of different thickness can be formed on the same semiconductor substrate.
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