Patent ID: 7781293

Claim:
A method of fabricating a semiconductor device, comprising: forming a gate insulating film on a semiconductor substrate including a memory cell region and a peripheral circuit region; forming a polycrystalline silicon film on the gate insulating film; forming a silicon nitride film on the polycrystalline silicon film; forming a silicon oxide film on the silicon nitride film; etching the silicon oxide film, the silicon nitride film, the polycrystalline silicon film and the gate insulating film in a predetermined pattern including a first opening width corresponding to a first trench in the memory cell region and a second opening width corresponding to a second trench in the peripheral circuit region, the second opening width being larger than the first opening width; and etching the semiconductor substrate to simultaneously form the first and second trenches with an etching gas made by mixing a halogen gas, a fluorocarbon gas and oxygen so that a first depth of the first trench is equal to a second depth of the second trench, and a first angle which is defined between a first side surface and a first bottom surface of the first trench is smaller than a second angle which is defined between a second side surface and a second bottom surface of the second trench, and the first trench includes a curved portion at an upper portion of the first side surface.