Nonvolatile semiconductor memory device
A nonvolatile semiconductor memory device comprises a cell unit including a first and a second selection gate transistor and a memory string provided between the first and second selection gate transistors and composed of a plurality of serially connected electrically erasable programmable memory cells operative to store effective data; and a data write circuit operative to write data into the memory cell, wherein the number of program stages for at least one of memory cells on both ends of the memory string is lower than the number of program stages for other memory cells, and the data write circuit executes the first stage program to the memory cell having the number of program stages lower than the number of program stages for the other memory cells after the first stage program to the other memory cells.
1. A nonvolatile semiconductor memory device, comprising:
a cell unit including:
a first selection gate transistor,
a second selection gate transistor, and
a plurality of serially-connected memory cells provided between the first selection gate transistor and the second selection gate transistor; and
a data write circuit configured to execute a writing operation to write data to the memory cells;
wherein
the memory cells include:
a first memory cell connected with a first word line and capable of being programmable in D 1 stages to thereby store data of D 1 bits, D 1 being an integer of 2 or more,
a second memory cell connected with a second word line and capable of being programmable in D 2 stages to thereby store data of D 2 bits, D 2 being an integer of 3 or more, the second memory cell being closer to the first selection gate transistor than the first memory cell, and
a third memory cell connected with a third word line and capable of being programmable in D 3 stages to thereby store data of D 3 bits, D 3 being an integer of 3 or more, the third memory cell being closer to the first selection gate transistor than the second memory cell; and
the data write circuit executes:
a first program on the third memory cell as first one of the D 3 stages,
a second program on the second memory cell as first one of the D 2 stages, after the first program,
a third program on the third memory cell as second one of the D 3 stages, after the second program,
a fourth program on the first memory cell as first one of the D 1 stages, after the third program, and
a fifth program on the first memory cell as second one of the D 1 stages, after the fourth program.
2. The nonvolatile semiconductor memory device according to claim 1 , wherein
the data write circuit further executes
a sixth program on the second memory cell as second one of the D 2 stages, after the fourth program and before the fifth program.
3. The nonvolatile semiconductor memory device according to claim 1 , wherein
the data write circuit further executes
a seventh program on the third memory cell as third one of the D 3 stages, after the fourth program and before the fifth program.
4. The nonvolatile semiconductor memory device according to claim 1 , wherein
the data write circuit further executes
an eighth program on the second memory cell as third one of the D 2 stages, after the fifth program.
5. The nonvolatile semiconductor memory device according to claim 2 , wherein
D 1 is 2,
D 2 is 3, and
D 3 is 3.
6. The nonvolatile semiconductor memory device according to claim 1 , wherein
the cell unit includes:
a first dummy cell having a structure same as one of the memory cells between the second selection gate transistor and the first memory cell, and
a second dummy cell having a structure same as one of the memory cells between the first selection gate transistor and the third memory cell.
7. A nonvolatile semiconductor memory device, comprising:
a cell unit including:
a first and a second selection gate transistor, and
a memory string provided between said first and second selection gate transistors and composed of a plurality of serially connected electrically erasable programmable memory cells capable of storing effective data; and
a data write circuit configured to execute writing data to the memory cells, the writing data having one or more program stages;
wherein
the memory cells include:
a first memory cell, to execute an M 1 -stage program, M 1 =an integer of 1 or more,
a second memory cell, to execute an M 2 -stage program, M 2 =an integer larger than M 1 , and being closer to the first selection gate transistor as compared with the first memory cell, and
a third memory cell, to execute an M 3 -stage program, M 3 =an integer larger than M 1 , and being closer to the first selection gate transistor as compared with the second memory cell; and
the data write circuit:
executes
the m 2 -th stage program, m 2 =an integer of 1 to M 2 ,
to the second memory cell
after execution of the m 2 -th stage program to the third memory cell,
executes
the m 1 -th stage program, m 1 =an integer of 1 to M 1 ,
to the second memory cell,
executes
the (m 1 +1)-th stage program
to the second memory cell
after execution of the m 1 -th stage program to the second memory cell, and
executes
the m 1 -th stage program
to the first memory cell
after execution of the (m 1 +1)-th stage program to the second memory cell.
8. The nonvolatile semiconductor memory device according to claim 7 , wherein
m 1 is 1.
9. The nonvolatile semiconductor memory device according to claim 7 , wherein
the second memory cell is closest to the first memory cell among memory cells to be executed the M 2 -stage program.
10. The nonvolatile semiconductor memory device according to claim 7 , wherein
M 3 is M 1 +2 or more.
11. The nonvolatile semiconductor memory device according to claim 9 , wherein
the third memory cell is adjacent to the second memory cell.
12. The nonvolatile semiconductor memory device according to claim 7 , wherein
the cell unit includes a dummy cell having a structure same as one of the memory cells between the first selection gate transistor and the memory string and/or between the second selection gate transistor and the memory string.