Semiconductor device including sidewall floating gates

1. A semiconductor device comprising:

polysilicon gate electrodes on a semiconductor substrate;

a metal silicide layer on the polysilicon gate electrodes;

a gate oxide layer between the polysilicon gate electrodes and the semiconductor substrate;

sidewall floating gates having an amount or concentration of electrons or holes under side portions of the polysilicon gate electrodes sufficient to adjust a threshold voltage of the device and form an inversion layer in the substrate under the sidewall floating gates without application of a bias to the sidewall floating gates;

a block oxide layer between the polysilicon gate electrodes and the sidewall floating gates;

source/drain areas in the substrate on each side of the polysilicon gate electrodes;

a virtual source/drain extension area in the substrate between the source/drain areas; and

sidewall spacers adjacent to the polysilicon gate electrodes and the sidewall floating gates.

2. The device as defined by claim 1 , further comprising an insulator layer between the sidewall spacers and the polysilicon gate electrodes, between the sidewall spacers and the sidewall floating gates, and on a top surface of the polysilicon electrodes.

3. The device as defined by claim 1 , wherein the polysilicon gate electrode has an upper part having a larger width than a corresponding lower part of the polysilicon gate electrode.

4. The device as defined by claim 1 , further comprising a block dielectric layer between the sidewall floating gates and the semiconductor substrate.

5. The device as defined by claim 1 , wherein the polysilicon gate electrodes have concave lower side surfaces, and the sidewall floating gates have an adjacent, convex surface complementary to the concave lower side surfaces of the polysilicon gate electrodes.

6. The device as defined by claim 1 , wherein the sidewall spacers comprise silicon nitride.

7. The device as defined by claim 1 , wherein the device is an NMOS transistor and positive electric charges are injected into the sidewall floating gates.

8. The device as defined by claim 1 , wherein the device is a PMOS transistor and negative electric charges are injected into the sidewall floating gates.

9. The device as defined by claim 1 , wherein the virtual source/drain extension areas have a depth of about 5 Å or less.

10. A semiconductor device comprising:

polysilicon gate electrodes on a semiconductor substrate;

a gate oxide layer between the polysilicon gate electrodes and the semiconductor substrate;

sidewall floating gates having an amount or concentration of electrons or holes under side portions of the polysilicon gate electrodes sufficient to adjust a threshold voltage of the device and form an inversion layer in the substrate under the sidewall floating gates without application of a bias to the sidewall floating gate; a block oxide layer between the polysilicon gate electrodes and the sidewall floating gates;

source/drain areas in the substrate on each side of the polysilicon gate electrodes;

a virtual source/drain extension area in the substrate between the source/drain areas;

sidewall spacers adjacent to the polysilicon gate electrodes and the sidewall floating gates; and

an insulator layer between the sidewall spacers and the polysilicon gate electrodes, between the sidewall spacers and the sidewall floating gates, and on a top surface of the polysilicon gate electrodes.

11. The device as defined by claim 10 , wherein the gate oxide layer is on a portion of the substrate between the sidewall floating gates.

12. The device as defined by claim 10 , wherein the sidewall floating gates comprise (poly)silicon, a metal, a metal alloy, or a conductive compound.

13. The device as defined by claim 12 , wherein the sidewall floating gates comprise polysilicon doped with a high concentration of N-type impurity atoms.

14. The device as defined by claim 13 , wherein the concentration of N-type impurity atoms is 1.0×10 17 ions/cm 3 or more.

15. The device as defined by claim 14 , wherein positive charges of 2.0×10 −6 C/cm 3 or more are injected into the sidewall floating gates.

16. The device as defined by claim 10 , wherein the sidewall spacers comprise silicon nitride.

17. The device as defined by claim 16 , wherein the insulator layer comprises an oxide.

18. The device as defined by claim 17 , wherein the insulator layer comprises silicon oxide.

19. The device as defined by claim 10 , wherein the insulator layer comprises an oxide formed by oxidizing a surface of the polysilicon gate and the sidewall floating gates.

20. The device as defined by claim 10 , wherein the amount or concentration of additional electrons or holes comprises an amount of holes sufficient to decrease a parasitic resistance of a virtual source/drain extension area in the substrate between the source/drain areas.

21. The device as defined by claim 10 , wherein the amount or concentration of additional electrons or holes is sufficient to increase a parasitic resistance of a virtual source/drain extension area in the substrate between the source/drain areas.

22. The device as defined by claim 10 , wherein the device is an NMOS transistor and positive electric charges are injected into the sidewall floating gates.

23. The device as defined by claim 10 , wherein the device is a PMOS transistor and negative electric charges are injected into the sidewall floating gates.

24. The device as defined by claim 10 , wherein the virtual source/drain extension areas have a depth of about 5 Å or less.

25. The device as defined by claim 10 , further comprising a block dielectric layer between the sidewall floating gates and the semiconductor substrate.

26. The device as defined by claim 25 , wherein a coupling ratio between the block dielectric layer and the block oxide is 0.5 or more.

27. The device as defined by claim 25 , wherein the block oxide is thinner than the block dielectric layer.

28. The device as defined by claim 25 , wherein the block oxide comprises a material having a dielectric constant higher than that of the block dielectric layer.