Fabrication of flash memory device involves performing trench formation process and wall oxide film formation process separately depending on pattern density, and forming wall oxide films with different thicknesses

摘要

A flash memory device is fabricated by performing a trench formation process and a wall oxide film formation process separately depending on a pattern density, and forming wall oxide films with different thicknesses. Fabrication of a flash memory device involves: (a) sequentially forming a tunnel oxide film (12), a polysilicon film (13), and a hard mask film (14) on a semiconductor substrate (11) in which a first region and a second region are defined; (b) etching the hard mask film, the polysilicon film, and the tunnel oxide film in the first region, and then etching the semiconductor substrate at a given depth to form a first trench; (c) forming a first wall oxide film (16) on the first trench; forming a first insulating film (17) on the entire surface to bury the first trench; (d) etching the hard mask film, the polysilicon film and the tunnel oxide film in the second region, and then etching the semiconductor substrate at a given depth to form a second trench; (e) forming a second wall oxide film (19) on the second trench; (f) forming a second insulating film (20) on the entire surface to bury the second trench; and (g) polishing the insulating films and then removing the hard mask film.