Semiconductor memory and its production process

1. A semiconductor memory comprising:

a first conductivity type semiconductor substrate and

memory cells each constituted of an island-like semiconductor layer, a charge storage layer and a control gate, the charge storage layer and the control gate being formed to entirely or partially encircle a sidewall of the island-like semiconductor layer,

wherein the memory cells are disposed in series, and the island-like semiconductor layer on which the memory cells are disposed has cross-sectional areas in a horizontal direction which vary stepwise.

2. A semiconductor memory according to claim 1 , wherein the cross-sectional areas decrease sequentially from a semiconductor substrate side to the top.

3. A semiconductor memory according to claim 1 , wherein the cross-sectional areas increase sequentially from a semiconductor substrate side to the top.

4. A semiconductor memory according to claim 1 , wherein at least one of the cross-sectional areas is equal to a cross-sectional area of the island-like semiconductor layer on a semiconductor substrate side.

5. A semiconductor memory according to claim 1 , wherein said one or more memory cells are electrically insulated from the semiconductor substrate by

a second conductivity type impurity diffusion layer formed in the semiconductor substrate or in the island-like semiconductor layer, or by

the second conductivity type impurity diffusion layer and a first conductivity type impurity diffusion layer formed in the second conductivity type impurity diffusion layer.

6. A semiconductor memory according to claim 1 , wherein a plurality of memory cells are formed in one island-like semiconductor layer and at least one of the memory cells is electrically insulated from another memory cell by

a second conductivity type impurity diffusion layer formed in the island-like semiconductor layer, or by

the second conductivity type impurity diffusion layer and a first conductivity type impurity diffusion layer formed in the second conductivity type impurity diffusion layer.

7. A semiconductor memory according to claim 1 , wherein said one or more memory cells are electrically insulated from the semiconductor substrate by

a second conductivity type impurity diffusion layer formed in the semiconductor substrate or the island-like semiconductor layer and

a depletion layer formed at a junction between the second conductivity type impurity diffusion layer and the semiconductor substrate or the island-like semiconductor layer.

8. A semiconductor memory according to claim 1 , wherein a plurality of memory cells are formed and at least one of the memory cells is electrically insulated from another memory cell by

a second conductivity type impurity diffusion layer formed in the island-like semiconductor layer and

a depletion layer formed at a junction between the second conductivity type impurity diffusion layer and the island-like semiconductor layer.

9. A semiconductor memory according to claim 1 , wherein a impurity diffusion layer is formed on the semiconductor substrate, the impurity diffusion layer functions as common wiring for at least one memory cell.

10. A semiconductor memory according to claim 1 ,

wherein a plurality of island-like semiconductor layers are formed in matrix,

wiring layers for reading a state of a charge stored in the memory cells are formed in the island-like semiconductor layers,

a plurality of control gates are arranged continuously in a direction to form a control gate line, and

a plurality of the wiring layers are connected in a direction crossing the control gate line to form a bit line.

11. A semiconductor memory according to claim 1 ,

wherein a gate electrode for selecting a memory cell is formed at least at an end of the memory cell formed on the island-like semiconductor layer so as to partially or entirely encircle the sidewall of the island-like semiconductor layer and the gate electrode is arranged in series with the memory cell.

12. A semiconductor memory according to claim 11 , wherein a part of the island-like semiconductor layer opposed to the gate electrode is electrically insulated from the semiconductor substrate or the memory cell by a second conductivity type impurity diffusion layer formed in the surface of the semiconductor substrate or in the island-like semiconductor layer.

13. A semiconductor memory according to claim 1 ,

wherein a second conductivity type impurity diffusion layer, or a second conductivity type impurity diffusion layer and a first conductivity type impurity diffusion layer formed in the second conductivity type impurity diffusion layer is/are formed partially or entirely at a corner of the island-like semiconductor layer having a stepwise structure in self-alignment with the charge storage layer so that channel layers of the memory cells are electrically connected to each other.

14. A semiconductor memory according to claim 11 ,

wherein a second conductivity type impurity diffusion layer, or a second conductivity type impurity diffusion layer and a first conductivity type impurity diffusion layer formed in the second conductivity type impurity diffusion layer is/are formed partially or entirely at a corner of the island-like semiconductor layer having a stepwise structure in self-alignment with the charge storage layer and the gate electrode so that a channel layer formed in a part of the island-like semiconductor layer opposed to the gate electrode and the channel layer of the memory cell are electrically connected.

15. A semiconductor memory according to claim 1 ,

wherein a plurality of memory cells are formed with regard to one island-like semiconductor layer and control gates constituting the memory cell are arranged so closely that cannel layers of memory cells are electrically connected.

16. A semiconductor memory according to claim 1 , wherein the control gate and the gate electrode are disposed so closely that a channel layer located in a part of the island-like semiconductor layer opposed to the gate electrode is electrically connected to a channel layer of the memory cell.

17. A semiconductor memory according to claim 1 , wherein a plurality of memory cells are formed with regard to one island-like semiconductor layer, and an electrode for electrically connecting cannel layers of memory cells is further formed between control gates.

18. A semiconductor memory according to claim 11 , wherein a plurality of memory cells are formed with regard to one island-like semiconductor layer, and an electrode for electrically connecting a channel layer located in a part of the island-like semiconductor layer opposed to the gate electrode to a channel layer of the memory cell is further formed between the control gate and the gate electrode.

19. A semiconductor memory according to claim 11 , wherein all, some or one control gate(s) are formed of the same material as all, some or one gate electrode(s).

20. A semiconductor memory according to claim 11 , wherein the charge storage layer and the gate electrode are formed of the same material.

21. A semiconductor memory according to claim 1 , wherein a plurality of island-like semiconductor layers are formed in matrix, and the width of the island-like semiconductor layers in one direction is smaller than a distance between adjacent island-like semiconductor layers in the same direction.

22. A semiconductor memory according to claim 1 , wherein a plurality of island-like semiconductor layers are formed in matrix, and a distance between the island-like semiconductor layers in one direction is smaller than a distance between the island-like semiconductor layers in another direction.