Implementation of an inhibit during soft programming to tighten an erase voltage distribution

摘要

Methods and apparatus for tightening an erased bit threshold voltage distribution are disclosed. According to one aspect of the present invention, a method for processing erased bits associated with an erased bit distribution which includes an over-erased bit which has a first value that is less than a first threshold voltage value and a bit that has a second value that substantially exceeds a second threshold voltage value includes inhibiting the fast bit. The method also includes applying a soft program pulse to the erased bits such that inhibiting the fast bit substantially prevents the second value from changing and applying the soft program pulse to the over-erased bit substantially causes the first value to increase. In one embodiment, applying the soft program pulse to the over-erased bit substantially causes the first value to increase to a value that is greater than or equal to the first threshold voltage value.