Patent ID: 7672168
Filing Date: 2010-03-02
Classification: G11C,H01L

Abstract:
1. A non-volatile semiconductor memory device comprising: a plurality of electrically data rewritable non-volatile semiconductor memory cells; a memory cell array in which the plurality of memory cells or memory cell units are arranged in matrix, the memory cell unit including at least one of the memory cells; a plurality of word lines connected to gates of the memory cells; a write circuit configured to write data in a plurality of selected memory cells in the memory cells, the plurality of selected memory cells being connected to a selected word line, the write circuit writing a data in the plurality of selected memory cells by supplying a write voltage to the selected word line; and a write verify circuit configured to perform write verify operation for the plurality of selected memory cells by supplying a first write verify voltage and a second write verify voltage to the selected word line; wherein write step operations and write verify operations are repeated when writing data into the plurality of selected memory cells, the write voltage is supplied to the selected word line in each of the write step operations, a first step write verify operation and a second step write verify operation are performed between (n-th) write step operation and (n+1-th) write step operation (where n is a natural number), the first write verify voltage and the second write verify voltage are respectively supplied to the selected word line in the first step write verify operation and the second step write verify operation, the first write verify voltage and the second write verify voltage are different from each other; and wherein there are plurality of distributions of threshold value of the memory cells, the plurality of distributions of threshold value includes a first distribution of threshold value and a second distribution of threshold value, the second distribution of threshold value has higher threshold values than the first distribution of threshold value, there is no distribution of threshold value between the first distribution of threshold value and the second distribution of threshold value, both the first write verify voltage and the second write verify voltage are higher than a center value of the first distribution of threshold value, both the first write verify voltage and the second write verify voltage are lower than a center value of the second distribution of threshold value, and the write voltage increases with a stepwise increment of predetermined voltage as the write step operation is repeated.