Patent ID: 6964913

Claim:
A method for forming a floating gate in a flash memory device, comprising the steps of: (a) providing a semiconductor substrate on which a tunnel oxide film and a first polysilicon film are formed; (b) sequentially forming a buffer oxide film and a pad nitride film on the first polysilicon film; (c) forming a trench in the semiconductor substrate; (d) depositing a device isolation oxide film to fill the trench, and then performing a planarization process using the pad nitride film as a barrier; (e) carrying out a strip process to simultaneously remove the pad nitride film and at least 50% of the buffer oxide film, leaving a reduced buffer oxide film on the first polysilicon film; (f) removing the reduced buffer oxide film using a pre-treatment cleaning process; and (g) depositing a second polysilicon film on the resulting structure and patterning the second polysilicon film with a patterning process, to form the floating gate including the first polysilicon film and the second polysilicon film.