Method of forming isolation layer of flash memory device

A method of forming an isolation layer of a flash memory device, the method comprising:

• providing a semiconductor substrate in which a tunnel insulating film, a conductive film, and a first insulating film are formed in an active region, and a trench is formed in an isolation region;
• forming a sidewall insulating film, a second insulating film, and a third insulating film so that the trench is gap filled, thus forming an isolation layer;
• removing the first insulating film, wherein top surfaces of the third insulating film and the second insulating film are etched, and the top surfaces of the third insulating film and the sidewall insulating film remain in a projected shape;
• and
• performing an etch process so that a top of sidewalls of the conductive film is exposed as the projections of the third insulating film and the sidewall insulating film are removed.