Method of manufacturing an integrated circuit having a charge coupled device and a MOS transistor

A method of manufacturing an integrated circuit having a charge coupled device and first and second MOS transistors, comprising:

• a) preparing a semiconductor substrate having a main surface including a first area, a second area and a third area, said second area including a well region for said first MOS transistor, said third area including a well region for said second MOS transistor;
• b) forming an anti-oxidation insulating film over the surface of the first area and the second area;
• c) forming a first silicon layer on the anti-oxidation insulating film of the first area;
• d) forming a second silicon layer on the anti-oxidation insulating film of the second area as a gate electrode of the first MOS transistor;
• e) forming a lower gate electrode of the charge coupled device covered with an oxide film, by thermal oxidizing the first silicon layer;
• f) forming a conductive layer as an upper gate electrode of the charge coupled device continuously over the anti-oxidation insulating film and the oxide film;
• and
• g) after the step f), forming a gate insulating film of the second MOS transistor on the surface of the third area.