Nonvolatile semiconductor memory transistor and method for manufacturing nonvolatile semiconductor memory

1. A method for manufacturing a nonvolatile semiconductor memory including a floating gate arranged so as to surround an outer periphery of an island-shaped semiconductor with a tunnel insulating film interposed between the floating gate and the island-shaped semiconductor, a control gate arranged so as to surround an outer periphery of the floating gate with a second insulating film interposed between the control gate and the floating gate, and a control gate line electrically connected to the control gate and extending in a predetermined direction, the method comprising:

a step of forming a plurality of island-shaped semiconductors on a source line formed at a predetermined position on a substrate;

a step of forming a first insulating film between the island-shaped semiconductors that are adjacent to each other and on the source line;

a step of forming a floating gate film by depositing a conductive material on the first insulating film;

a step of forming a resist on the floating gate film, the resist having a groove extending in a direction perpendicular to the predetermined direction in which the control gate line extends;

a step of forming a floating gate for each of the island-shaped semiconductors using the resist by separating the floating gate film from a portion that is a lower region of the groove and that is on the first insulating film by etching;

a step of forming the second insulating film on the floating gate;

a step of forming, on the second insulating film, a control gate that surrounds an outer periphery of each of the island-shaped semiconductors;

a step of forming the control gate line connecting the control gates of adjacent island-shaped semiconductors among the island-shaped semiconductors; and

a step of etching the floating gates so that the control gates and the floating gates overlap one another in a vertical direction with the second insulating film therebetween.

2. A nonvolatile semiconductor memory transistor comprising:

an island-shaped semiconductor having a source region, a channel region, and a drain region formed in the order of the source region, the channel region, and the drain region from the side of a substrate;

a floating gate arranged so as to surround an outer periphery of the channel region in such a manner that a tunnel insulating film is interposed between the floating gate and the channel region;

a control gate arranged so as to surround an outer periphery of the floating gate in such a manner that an inter-polysilicon insulating film is interposed between the control gate and the floating gate; and

a control gate line electrically connected to the control gate and extending in a predetermined direction,

wherein the floating gate extends to regions below and above the control gate and to a region below the control gate line,

wherein the inter-polysilicon insulating film is arranged so as to be interposed between the floating gate and an upper surface, a lower surface, and an inner side surface of the control gate, and

wherein the inter-polysilicon insulating film is arranged so as to be interposed between the control gate line and a portion of the floating gate that extends to the region below the control gate line.

3. The nonvolatile semiconductor memory transistor according to claim 2 , further comprising a first insulating film arranged on the substrate so as to be located below the floating gate, the first insulating film being thicker than at least one of the tunnel insulating film and the inter-polysilicon insulating film.