US Patent 7368342 Semiconductor device and method of manufacturing the same

A method for manufacturing a semiconductor device includes forming a gate-insulating film on a semiconductor substrate; forming a gate electrode on the gate-insulating film to be electrically insulated from the semiconductor substrate; etching the gate electrode, the gate insulating film and the semiconductor substrate to form a trench which is used to electrically isolate a device region for forming a device from the remainder region on the substrate top surface; and etching the inside of the trench using a gas containing Cl2 and HBr with a different condition from the etching condition of the semiconductor substrate.