Nonvolatile semiconductor memory device and its manufacturing method

1. A nonvolatile semiconductor memory device, comprising:

a semiconductor substrate of a first conductive type;

first and second diffused layers of a second conductive type on the surface of the semiconductor substrate, with a channel region of the semiconductor substrate therebetween;

first and second laminated films above edge portions of the channel region and above edge portions of, respectively, the first and the second diffused layers, each laminated film being laminated from the semiconductor substrate and the respective diffused layer in the order of a first insulating layer as a first film, a second insulating layer or a semiconductor layer as a second film, and a third insulating layer as a third film;

a fourth insulating layer on the semiconductive substrate channel region at a location where the laminated films are absent;

each of the second insulating layers or each of the semiconductor layers having a fifth insulating layer on a side wall thereof; and

a gate electrode comprising a first conductive film on the fourth insulating layer and second and third conductive films of the first and second laminated films, respectively, the gate electrode entirely overlying the upper sides of fourth insulating layer, the first laminated film, and the second laminated film.

2. A nonvolatile semiconductor memory device according to claim 1 , wherein:

the capacitance value per unit area of the fourth insulating layer is larger than the capacitance value per unit area of the laminated films.

3. A nonvolatile semiconductor memory device according to claim 1 , wherein:

the third insulating layer of the third film of each of the laminated films comprises a silicon oxide film;

the second insulating layer of the second film of each of the laminated films comprises a silicon nitride film;

the first insulating layer of the first film of each of the laminated films comprises a silicon oxide film, and

each fifth insulating layer comprises a silicon oxide film.

4. A nonvolatile semiconductor memory device according to claim 1 , wherein:

the third insulating layer of the third film of each of the laminated films comprises a silicon oxide film;

the semiconductor layer of the second film of each of the laminated films comprises a silicon film;

the first insulating layer of the first film of each of the laminated films comprises a silicon oxide film; and

each fifth insulating layer comprises a silicon oxide film.

5. A nonvolatile semiconductor memory device according to claim 1 , wherein:

the cross section of the gate electrode has a T shape.

6. A nonvolatile semiconductor memory device according to claim 1 , wherein:

an end of each of the second and the third conductive films overlaps a respective one of the first diffused layer and the second diffused layer through the respective one of the laminated films.

7. A nonvolatile semiconductor memory device according to claim 1 , wherein:

the first conductive film comprises a material different from the material of the second conductive film and the third conductive film.

8. A nonvolatile semiconductor memory device according to claim 1 , wherein said gate electrode further comprises:

an insulating film between the side walls of the first conductive film and the side walls of the second conductive film and the third conductive film.

9. A nonvolatile semiconductor memory device according to claim 1 , wherein:

the laminated films are restrictively formed on the upper sides of the edge portions of the channel region and the upper sides of the edge portions of the respective ones of the first and second diffused layers.

10. A nonvolatile semiconductor memory device according to claim 1 , wherein:

the gate electrode is connected to a word line of a memory cell; and

the first diffused layer or the second diffused layer functions as a part of a bit line of the memory cell.

11. A nonvolatile semiconductor memory device according to claim 1 , wherein:

the second and third conductive films contact the first conductive film to provide a continuous conductive film layer as the gate electrode.

12. A nonvolatile semiconductor memory device according to claim 1 , wherein:

each of the second conductive film and the third conductive film comprises a first gate electrode end adjacent the first conductive film and a second gate electrode end adjacent the respective first gate electrode end.

13. A nonvolatile semiconductor memory device according to claim 1 , wherein:

each fifth insulating layer is on an external side wall of the respective second insulating layer or semiconductor layer, and

each second insulating layer or semiconductor layer has a sixth insulating layer on an internal side wall thereof, adjacent the first conductive film.

14. A nonvolatile semiconductor memory device according to claim 1 , wherein:

the laminated films are on the upper sides of the edge portions of the channel region and the upper sides of the respective ones of the first and second diffused layers.

15. A nonvolatile semiconductor memory device according to claim 14 , wherein:

the second and third conductive films are on the laminated films and the upper sides of the respective ones of the first and second diffused layers.

16. A nonvolatile semiconductor memory device according to claim 11 , wherein:

the first conductive film, the second conductive film, and the third conductive film comprise a single film.

17. A nonvolatile semiconductor memory device, comprising:

a semiconductor substrate;

a first diffused layer and a second diffused layer on the surface of the semiconductor substrate, with a channel region of the semiconductor substrate between the first and second diffused layers;

a first insulating layer, an isolated substance and a third insulating layer in order on the upper side of each end portion of the channel region, adjacent to the first diffused layer and the second diffused layer;

a fourth insulating layer on the channel region in location having no first insulating layer, no isolated substance and no third insulating layer; and

a gate electrode entirely covering the upper sides of the first insulating layer, the isolated substance, the third insulating layer and the fourth insulating layer.

18. A nonvolatile semiconductor memory device according to claim 17 , wherein:

each of the first insulating layer and the third insulating layer comprises a silicon oxide film; and

the isolated substance comprises silicon nitride, silicon, silicon germanium or high-melting point metal.

19. A nonvolatile semiconductor memory device according to claim 17 , wherein:

the capacitance value per unit area of the fourth insulating layer is larger than the capacitance value per unit area of the combined first insulating layer, isolated substance, and third insulating layer.

20. A nonvolatile semiconductor memory device according to claim 17 , wherein:

the gate electrode comprises a continuous conductive film layer.

21. A nonvolatile semiconductor memory device according to claim 17 , wherein:

the gate electrode comprises a conductive film, a first pair of gate electrode ends adjacent respective ends of the conductive film, and a second pair of gate electrode ends adjacent respective ones of the first gate electrode ends.