Method of manufacturing flash memory device with conductive spacers

A method of manufacturing a flash memory device, comprising:

• providing a semiconductor substrate in which a plurality of regions including a cell region and a high-voltage transistor region are defined;
• etching a surface of the semiconductor substrate of the high-voltage transistor region so that a height of the cell region of the semiconductor substrate is higher than that of the high-voltage transistor region;
• forming a tunnel oxide film on a non-etched semiconductor substrate of the cell region;
• forming a single gate oxide film on the etched semiconductor substrate of the high-voltage transistor region;
• forming a first conductive layer and a hard mask film over the tunnel oxide film and the gate oxide film;
• etching the hard mask film, the first conductive layer, and the semiconductor substrate to form a trench;
• filling the trench with an insulating film to form an isolation film;
• etching an upper portion of the isolation film formed in the cell region and the high-voltage transistor region;
• and
• forming a dielectric film and a second conductive layer on the first conductive layer;
• and
• patterning the second conductive layer to form a cell gate and a high-voltage transistor gate,
• wherein the tunnel oxide film and the single gate oxide film are formed by performing oxidization.