Method of manufacturing flash memory device

A method of manufacturing a flash memory device, comprising the steps of:

• sequentially forming a pad oxide film and a pad nitride film on a semiconductor substrate;
• forming a plurality of isolating trenches in the semiconductor substrate by means of a shallow trench isolation process using the patterned pad oxide film and the pad nitride film as an etch mask;
• performing a wall oxidization process and then removing the pad nitride film and the pad oxide film;
• forming a gap fill oxide film on the entire structure of the semiconductor substrate so that the plurality of the isolating trenches are sufficiently buried;
• polishing and planarizing the gap fill oxide film by means of a chemical mechanical polishing process;
• etching a portion of the polished gap fill oxide film to form a plurality of oxide film line patterns and a plurality of isolating cell isolation films;
• forming tunnel oxide films and conductive layers for a floating gate at an exposed portion of the semiconductor substrate;
• patterning the conductive layers for the floating gate by means of an etch process using the floating gate mask;
• sequentially forming a dielectric film, a conductive layer for a control gate and a hard mask layer on the entire structure including the conductive layers for the floating gate;
• patterning the conductive layers for the control gate by means of an etch process using a mask for the control gate, thus forming a plurality of control gates;
• performing a self-aligned etch process to etch exposed portions of the conductive layers for the floating gate, thus forming a plurality of floating gate;
• and
• removing exposed portions of the oxide film line patterns by means of the self-aligned source etch process and then forming a plurality of drains and a plurality of common source lines by means of a cell source/drain implantation process.