Programming which can make threshold voltages of programmed memory cells have a narrow distribution in a nonvolatile semiconductor memory
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United States of America Patent
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May 26, 1998
Grant Date -
N/A
app pub date -
Jun 3, 1997
filing date -
Jun 3, 1996
priority date (Note) -
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Abstract
On programming a selected memory cell of a nonvolatile semiconductor memory, first programming (S11) of the selected memory cell is made by applying a first programming pulse to the selected memory cell to make the selected memory cell have a programmed threshold voltage (Vtm). First verification (S12) is made whether the selected memory cell has the programmed threshold voltage which is not greater than a first predetermined upper limit voltage (Vt1). When the selected memory cell has the programmed threshold voltage greater than the Vt1, the first programming is again made. When the selected memory cell has the programmed threshold voltage not greater than the Vt1, second verification (S13) is made whether the selected memory cell has the programmed threshold voltage which is not greater than a second predetermined upper limit voltage (Vt10) less than the Vt1. When the selected memory cell has the programmed threshold voltage greater than the Vt10, second programming (S13) of the selected memory cell by applying a second programming pulse different from the first programming pulse to the selected memory cell so as to make the selected memory cell have the programmed threshold voltage which is not greater than the Vt10. When the selected memory cell has the programmed threshold voltage not greater than the Vt10, programming of the selected memory cell is completed.
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