Patent ID: 7693667

Claim:
A method of determining a predicted flash endurance Vt of a flash cell after N program/erase cycles, the method comprising the steps of: determining a pair of Ctp or Cte values of the flash cell at different respective cycle numbers in a range from 2000 to less than N program/erase cycles; determining a Ctp or Cte slope, R, of a line between the pair of Ctp or Cte values in a half logarithmic graph representation; measuring a Vtp value and a Vte value of the flash cell after a cycle number in a range from 2000 to less than N/2 program/erase cycles; calculating a Vtp slope, S, of a line starting from the measured Vtp value in a half logarithmic graph representation based on a first transformation function describing a relationship between an average of Ctp and Cte slopes and an average of Vtp slopes of historical test data from flash cells of wafers having substantially the same process steps compared to the flash cell under investigation; calculating a Vte slope, S′, of a line starting from the measured Vte value in a half logarithmic graph representation based on R and a second transformation function describing a relationship between an average of Ctp and Cte slopes and an average of Vte slopes of the historical test data; and determining the Vtp and Vte values at 2 million program/erase cycles by extrapolating from the measured Vte and Vtp values using S and S′ respectively in half logarithmic graph representations.