Methods of fabricating nonvolatile memory device

A method of fabricating a nonvolatile memory device comprising:

• forming a nonvolatile memory structure, including:
• implanting first ions into an active region of a semiconductor substrate to form a first well and to adjust a threshold voltage of a low voltage n-type MOS transistor and a threshold voltage of a high voltage n-type MOS transistor;
• implanting second ions into active region of the semiconductor substrate to form a second well and to adjust a threshold voltage of a high voltage p-type MOS transistor and a threshold voltage of a low voltage p-type MOS transistor, thereby forming a conductive region;
• depositing an ONO layer on the semiconductor substrate;
• patterning and etching the ONO layer to form an ONO structure;
• after forming the ONO structure, forming a first gate oxide layer on the semiconductor substrate;
• removing the first gate oxide layer existing where the low voltage n-type MOS transistor and the low voltage p-type MOS transistor are to be formed;
• and
• forming a second gate oxide layer for the low voltage n-type MOS transistor and the low voltage p-type MOS transistor;
• and
• after forming the nonvolatile memory structure, forming a logic circuit.