Method of manufacturing semiconductor device

A method of manufacturing a semiconductor device, comprising the steps of:

• forming a top surface nitride film on a top surface of a substrate;
• patterning said top surface nitride film so as to form an opening in said top surface nitride film;
• and
• forming a second oxide film on a bottom surface of said substrate while forming a first oxide film on a surface portion of said substrate which is exposed by said opening.

A method of manufacturing a semiconductor device, comprising the steps of:

• forming a bottom surface polysilicon on a bottom surface of a substrate having a top surface oxide film formed on a top surface thereof, said top surface oxide film being exposed on a top surface side of said substrate, said bottom surface polysilicon being exposed on a bottom surface side of said substrate;
• and
• removing said exposed top surface oxide film by wet etching while leaving said exposed bottom surface polysilicon intact;
• wherein said substrate has a buried oxide film on said top surface side thereof and a bottom surface oxide film on said bottom surface side thereof.