Patent ID: 8258565

Claim:
A nonvolatile semiconductor memory device, comprising: a semiconductor substrate; a tunnel insulator on the semiconductor substrate; a floating gate electrode including a first floating gate electrode on the tunnel insulator and a second floating gate electrode on the first floating gate electrode, the second floating gate electrode including a conductive impurity element and being in a nondegenerate state; an intergate insulating film formed to cover at least continuously an upper and a portion of a side surface of the floating gate electrode; a control gate electrode on the intergate insulating film; and an isolation insulating film, a lower portion of the isolation insulating film being embedded in the semiconductor substrate in both sides of the floating gate electrode along a channel width direction, an upper portion of the isolation insulating film contacting with a side surface of the first floating gate electrode and protruding to a level between an upper surface of the semiconductor substrate and an upper surface of the first floating gate electrode.