Patent ID: 7297593

Claim:
A method of forming a floating gate of a flash memory device, the method comprising the steps of: sequentially depositing a screen oxide film, a hard mask nitride film, a hard mask buffer oxide film, and a hard mask polysilicon film on a semiconductor substrate and then performing a patterning process to expose the semiconductor substrate; etching the exposed semiconductor substrate to form trenches while removing the hard mask polysilicon film; depositing a high density plasma oxide film on the entire structure including the insides of the trenches and then stripping the high density plasma oxide film and the hard mask buffer oxide film using the hard mask nitride film as an etch stopper; stripping the hard mask nitride film using at least two wet chemical etching steps; after stripping the screen oxide film, depositing a tunnel oxide film and then depositing a floating gate polysilicon film on the entire structure including the tunnel oxide film; and, partially removing the high density plasma oxide film within the trenches to create recessions therein, and then rounding the upper edges of the floating gate polysilicon film, which upper edges are exposed by the creation of the recessions.