NONVOLATILE MEMORY DEVICE AND METHOD OF CONTROLLING THE SAME

A memory block is divided into sub blocks including a first sub block and a second sub block that are disposed in a vertical direction where the memory block includes a plurality of cell strings and each cell string includes a plurality of memory cells that are disposed in the vertical direction. A normal erase operation is performed independently with respect to each of the sub blocks. A disturbance verification read operation with respect to the first sub block is performed to determine whether a threshold voltage of memory cells connected to a wordline in an erased state of the first sub block is increased higher than a reference level. A post erase operation is selectively performed based on a result of the disturbance verification read operation to decrease the threshold voltage of memory cells in the erased state of the first sub block.