Nonvolatile memory device for preventing program disturbance and method of programming the nonvolatile memory device

A method of programming a selected memory cell of a memory cell array of a nonvolatile memory device in which a plurality of memory cells serially connected to a bit line constitute at least one cell string and are sequentially connected to a first word line, a second word line, and a third word line constituting a word line unit, the method comprising:

• driving, in a current program loop, a word line of the selected memory cell from among the first, second or third word line with a first program voltage;
• determining whether the selected memory cell is correctly programmed;
• sequentially driving the first word line with the first program voltage, the second word line with the first program voltage, and the third word line with the first program voltage;
• and
• when it is determined that the selected memory cell is not correctly programmed, the word line of the selected memory cell is driven with a second program voltage in a next program loop.