Semiconductor device and manufacturing method thereof

A method of manufacturing a semiconductor device, comprising:

• embedding a first insulating film for element isolation in a main surface of a semiconductor substrate to form a plurality of provisional active regions which extend in a first direction and are disposed in a repeating manner in a second direction which intersects said first direction;
• forming a sacrificial film covering the main surface;
• etching the first insulating film for element isolation, the sacrificial film and the semiconductor substrate to form a plurality of first trenches demarcating a plurality of first active regions which are obtained by dividing each of the plurality of provisional active regions in the first direction;
• embedding second insulating films for element isolation into the plurality of first trenches;
• removing the sacrificial film after the second insulating films for element isolation have been embedded into the plurality of first trenches;
• forming first side-wall insulating films covering side surfaces of parts of the second insulating films for element isolation, said parts projecting from an obverse surface of the main surface, after the sacrificial film has been removed;
• forming second side-wall insulating films covering side surfaces of the first side-wall insulating films;
• embedding cap insulating films into a plurality of second trenches which appear as a result of the formation of the second side-wall insulating films;
• forming a plurality of third trenches by removing the second side-wall insulating films while allowing the second insulating films for element isolation, the cap insulating films and the first side-wall insulating films to remain, and etching the semiconductor substrate using the second insulating films for element isolation, the cap insulating films and the first side-wall insulating films as a mask;
• and
• forming first wiring lines by forming first gate insulating films covering the inner surfaces of each of the plurality of third trenches, and embedding a first conductive film into a lower portion of each of the plurality of third trenches.