Semiconductor device and manufacturing method thereof

A method of manufacturing a semiconductor device comprising a semiconductor substrate including an active area surrounded by an isolation insulating film, a nonvolatile memory cell provided on the active area, the method comprising:

• forming a first insulating film as a tunnel insulating film and a first conductive film as a floating gate electrode sequentially on the semiconductor substrate;
• forming an isolation trench on a surface of the semiconductor substrate defining the active area and shapes of the floating gate electrode and the tunnel insulating film in a channel width direction of the nonvolatile memory cell by etching the first conductive film, the first insulating film and the semiconductor substrate, the isolation trench being formed such that relating to a cross section in the channel width direction of the nonvolatile memory cell, dimension of a top surface of the active area is shorter than dimension of a bottom surface of the tunnel insulating film;
• forming the isolation insulating film in the isolation trench;
• forming a second insulating film as interelectrode insulating film and a second conductive film as a control gate electrode on the first conductive film sequentially;
• and
• determining shapes of the control gate electrode, the interelectrode insulating film, the floating gate electrode and the tunnel insulating film by etching the second conductive film, the second insulating film, the first conductive film and the first insulating film sequentially.