Channel precharge and program methods of a nonvolatile memory device

1. A channel pre-charge method of a nonvolatile memory device including a cell string, comprising:

pre-charging a channel of the cell string according to a first word line bias condition; and

pre-charging the channel of the cell string according to a second word line bias condition different than the first word line bias condition.

2. The channel pre-charge method as claimed in claim 1 , wherein the cell string comprises:

a string selection transistor connected to a bit line, a plurality of memory cells, each of which is connected to a corresponding word line; and

a ground selection transistor connected to a common source line, wherein the plurality of memory cells is connected in series between the string selection transistor and the ground selection transistor.

3. The channel pre-charge method as claimed in claim 2 , wherein, during the first word line bias condition, all word lines are biased to a ground voltage.

4. The channel pre-charge method as claimed in claim 3 , wherein, during the first word line bias condition, the bit line is biased to one of a power supply voltage and the ground voltage according to data to be programmed, and the string selection transistor is biased to the power supply voltage.

5. The channel pre-charge method as claimed in claim 4 , wherein electrons in the channel of the cell string pre-charged during the first word line bias condition move to the bit line during the second word line bias condition.

6. The channel pre-charge method as claimed in claim 5 , wherein the second word line bias condition forms a potential well at a channel of a memory cell corresponding to an outer-most word line towards the bit line and moves additional electrons in the potential well to the bit line.

7. The channel pre-charge method as claimed in claim 6 , wherein the outer-most word line is a dummy word line.

8. The channel pre-charge method as claimed in claim 2 , wherein the second word line bias condition forms a potential well sequentially or stepwise at each channel of the plurality of memory cells corresponding to all or some of the word lines and moves electrons in the potential well of a memory cell corresponding to an outer-most word line toward the bit line.

9. The channel pre-charge method as claimed in claim 2 , wherein pre-charging the channel of the cell string according to the second word line bias condition is executed once or repeated.

10. A program method of a nonvolatile memory device including a plurality of cell strings, each of which is connected to a bit line and includes a plurality of memory cells connected in series to a corresponding bit line through a selection transistor, each of which is connected to a corresponding word line, the method comprising:

moving electrons from channels of the cell strings to the corresponding bit lines according to data to be programmed under a first word line bias condition;

moving additional electrons to the corresponding bit lines under a second word line bias condition that is different than the first word line bias condition and in which voltages of all or some of the word lines are controlled; and

supplying a program voltage and a pass voltage to selected word lines and non-selected word lines, respectively.

11. The program method as claimed in claim 10 , wherein the word lines all are biased to a ground voltage under the first word line bias condition.

12. The program method as claimed in claim 11 , wherein each of the bit lines is biased by one of a power supply voltage and the ground voltage according to data to be programmed and the string selection transistor is biased by the power supply voltage.

13. The program method as claimed in claim 10 , wherein the second word line bias condition forms a potential well sequentially at each of channels of the plurality of memory cells corresponding to all or some of the word lines and moves electrons in the potential well of a memory cell corresponding to an outer-most word line towards a bit line to the bit line.

14. The program method as claimed in claim 13 , wherein the additionally removing electrons to the corresponding bit line includes

setting the voltages of all or some of the word lines to a first word line voltage less than the pass voltage;

supplying a positive pulse voltage to all or some of the word lines sequentially; and

setting the outer-most word line toward the bit line to the first word line voltage.

15. The program method as claimed in claim 14 , wherein, when all or some of the word lines are set to the first word line voltage, the outer-most word line is set to a second word line voltage which is smaller than the pass voltage, the first word line voltage being one of the ground voltage and a negative voltage.

16. The program method as claimed in claim 15 , wherein the positive pulse voltage has the same level as the second word line voltage.

17. The program method as claimed in claim 13 , wherein the additionally removing electrons to the corresponding bit line includes

setting the voltages of the all or some of the word lines to a first word line voltage smaller than the pass voltage and changing the voltages of the all or some of the word lines to a second word line voltage sequentially, the second word line voltage being one of the ground voltage and a negative voltage.

18. The program method as claimed in claim 17 , wherein an outer-most word line toward a bit line and at least one of all or some of the word lines are set to the second word line voltage at the same time.

19. The program method as claimed in claim 13 , wherein the second word line bias condition is determined to form a potential well stepwise at each channel of the plurality of memory cells corresponding to all or some of the word lines.

20. The program method as claimed in claim 13 , wherein the additionally removing electrons to the corresponding bit line includes

setting the voltage of an outer-most word line toward a bit line to a first word line voltage and the remaining word lines to a second word line voltage;

setting all or some of the word lines to the first word line voltage smaller than the pass voltage;

supplying a positive pulse voltage to the all or some of the word lines sequentially; and

setting the outer-most word line toward the bit line to the first word line voltage.