Disclosed is a method of manufacturing the
flash memory device. The method comprises the steps of sequentially forming a tunnel
oxide film, a first polysilicon film and a
hard mask film on a
semiconductor substrate,
etching portions of the
hard mask film, the first polysilicon film, the tunnel
oxide film and the
semiconductor substrate through a patterning process to form a trench within the
semiconductor substrate, depositing an
oxide film to bury the trench and then
polishing the oxide film by means of a chemical mechanical
polishing process until the
hard mask film is exposed, removing the hard
mask film, implementing a cleaning process so that a protrusion of the oxide film is recessed to an extent that the sidewall bottom of the first polysilicon film is not exposed, depositing a second polysilicon film on the results in which the protrusion of the oxide film is recessed and then
polishing the second polysilicon film until the protrusion of the oxide film is exposed, forming a
dielectric film on the second polysilicon film, and forming a control gate on the
dielectric film.