Semiconductor device and manufacturing method thereof

A semiconductor device comprising:

• a semiconductor substrate;
• a first active area formed on the semiconductor substrate;
• a shallow trench isolation configured to surround the first active area;
• a first gate insulating film formed on the first active area;
• and
• a first gate electrode formed on the first gate insulating film, which has a first projection portion above the shallow trench isolation at one side and a second projection portion above the shallow trench isolation at the other side,
• wherein the first projection portion has a different length in a direction of the gate electrode from a length of the second projection portion.

A method for manufacturing a semiconductor device, the method comprising:

• forming a plurality of active areas having island-like shapes surrounded by an element isolation groove on a semiconductor substrate;
• embedding an element isolation film into the element isolation groove so as to be adjacent to the plurality of active areas;
• forming a plurality of gate insulating films respectively on the plurality of active areas;
• forming gate electrode material films on the plurality of element isolation films and the plurality of gate insulating films;
• forming mask patterns of a plurality of gate electrodes on the gate electrode material films;
• and
• performing an etching process on the gate electrode material films by use of the mask patterns, thereby forming a plurality of gate electrodes that respectively correspond to the plurality of active areas;
• and each includes:
• a first end portion that overhangs onto the element isolation film at one side in a first length;
• and
• a second end portion that overhangs onto the element isolation film at the other side in a second length that is different from the first length.