Nonvolatile memory device and method of programming the device

A method of programming a nonvolatile memory device, the method comprising:

• performing a first program operation on first memory cells selected to store first data, from among memory cells coupled to a selected word line, such that threshold voltages of the first memory cells each have a first target voltage corresponding to the first data;
• performing a first verification operation on the first memory cells using a first verification voltage;
• performing a second program operation on second memory cells selected to store second data, from among the memory cells coupled to the selected word line, such that threshold voltages of the second memory cells each have a second target voltage corresponding to the second data;
• detecting a memory cell having a threshold voltage less than the first target voltage using the first verification voltage, from among the first memory cells;
• performing a second verification operation for detecting a memory cell having a threshold voltage less than the second target voltage using a second verification voltage, from among the second memory cells;
• performing a third program operation on a memory cell such that the threshold voltage of the memory cell becomes more than the first target voltage upon detecting a memory cell from among the first memory cells having a threshold voltage less than the first target voltage;
• and
• performing a fourth program operation on a memory cell such that the threshold voltage of the memory cell becomes more than the second target voltage upon detecting a memory cell from among the second memory cells having a threshold voltage less than the second target voltage.