US Patent 7763516 Manufacturing method of semiconductor device having trench isolation

A manufacturing method of semiconductor device includes: forming a nitride film above a silicon substrate including a first region and a second region which respectively correspond to an outside of a memory cell region and the memory cell region; forming trenches reaching from the nitride film to the silicon substrate; retreating the nitride film such that widths of the trenches at the nitride film become wider; forming a buried oxide film to be buried in the trenches after the retreating; polishing the buried oxide film with the nitride film being used as a stopper; removing the nitride film after the polishing; implanting impurity after the removing; forming gate electrodes after the implanting; and implanting impurity after the forming the gate electrodes.