Nonvolatile semiconductor memory device and method of manufacturing the same

1. A nonvolatile semiconductor memory device comprising:

a first stack unit with a first selection transistor and a second selection transistor formed on a semiconductor substrate; and

a second stack unit with first insulating layers and first conductive layers alternately stacked on the upper surface of the first stack unit,

the second stack unit including

a second insulating layer vertically formed in contact with side walls of the first insulating layers and the first conductive layers,

a charge storage layer vertically formed in contact with the second insulating layer for storing electrical charges,

a third insulating layer vertically formed in contact with the charge storage layer, and

a first semiconductor layer formed in contact with the third insulating layer so as to extend in a stacking direction, with one end connected to one diffusion layer of the first selection transistor and the other end connected to a diffusion layer of the second selection transistor.

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

the first semiconductor layer has an inverted U-shaped cross sectional shape in a way of turning back at an upper portion in the stacking direction and contacting the first selection transistor and the second selection transistor at a lower portion.

3. The nonvolatile semiconductor memory device according to claim 2 , further comprising

a buried insulating film filling the inverted U-shaped portion of the first semiconductor layer.

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

the first selection transistor and the second selection transistor are planar-type transistor with the diffusion layer on the semiconductor substrate.

5. The nonvolatile semiconductor memory device according to claim 1 , further comprising

a third stack unit positioned on the second stack unit, wherein

the third stack unit includes:

a first contact plug layer connected to the other diffusion layer of the first selection transistor;

a first wiring layer formed in contact with the first contact plug layer, extending in a first direction orthogonal to the stacking direction;

a second contact plug layer connected to the other diffusion layer of the second selection transistor; and

a second wiring layer formed in contact with the second contact plug layer, extending in a second direction orthogonal to the first direction in a main plane of the semiconductor substrate.

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

the first conductive layer is formed of partially silicided polysilicon.

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

the first semiconductor layer is formed of partially silicided polysilicon.

8. The nonvolatile semiconductor memory device according to claim 1 , further comprising

a trench penetrating the second stack unit and reaching to the first stack unit, wherein

the second insulating layer, the charge storage layer, the third insulating layer, and the first semiconductor layer are formed in contact with the side walls of the first insulating layer and the first conductive layer facing the trench, and

the first selection transistor and the second selection transistor are insulation-separated by the insulating layer buried in the trench.

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

the first semiconductor layer has a U-shaped cross sectional shape in a trench penetrating the second stack unit and reaches to the first stack unit, and

the first semiconductor layer is connected to the diffusion layers of the first selection transistor and the second selection transistor respectively through a third contact plug layer and a fourth contact plug layer.

10. The nonvolatile semiconductor memory device according to claim 8 , wherein

a bottom of the trench reaches to a portion inside the semiconductor substrate.