Method of fabricating flash memory device
The present invention relates to a method of fabricating a flash memory device. According to the present invention, an oxide film is deposited and etched to form trenches, the trenches are filled with a metal film, and the metal film undergoes CMP to form bit lines. In this case, an etch stop layer of the trench etch process, a CMP stop layer of a CMP process and a wet barrier on the sides of the trenches are formed using a thermally treated SiON film having an etch rate lower than that of a wet chemical. As such, since a thickness and width of bit lines can be made uniform, bit line resistance and capacitance can be maintained constantly.
1. A method of fabricating a flash memory device, comprising the steps of:
(a) forming a first SiON film on a semiconductor substrate and thermally treating the first SiON film;
(b) forming an insulating film on the thermally treated first SiON film;
(c) forming a second SiON film on the insulating film and thermally treating the second SiON film;
(d) patterning the thermally treated second SiON film, the insulating film and the thermally treated first SiON film to form trenches;
(e) forming a third SiON film on the entire surface, thermally treating the third SiON film, and allowing the thermally treated third SiON film to remain on the sides of the trenches; and
(f) forming bit lines within the trenches.
2. The method as claimed in claim 1 , wherein the first SiON film is formed to a thickness from 150 Å to 300 Å.
3. The method as claimed in claim 1 , wherein a thermal treatment temperature of the step (a), (c) and (e) is from 500° to 850° C.
4. The method as claimed in claim 1 , wherein the thermal treatment process of the step (a), (c) and (e) is performed under an oxidization atmosphere and inert atmosphere.
5. The method as claimed in claim 1 , wherein the second SiON film is formed to a thickness from 200 Å to 500 Å.
6. The method as claimed in claim 1 , wherein the third SiON film is formed to a thickness from 30 Å to 100 Å.
7. The method as claimed in claim 1 , wherein the step (d) includes the steps of:
forming a hard mask film on the thermally treated second SiON film;
patterning the hard mask film and the thermally treated second SiON film by means of a photolithography process;
patterning the insulating film and the thermally treated first SiON film using the patterned hard mask film as a mask, forming trenches; and
removing the hard mask film.
8. The method as claimed in claim 7 , wherein the hard mask film is formed using a silicon nitride film.
9. The method as claimed in claim 7 , wherein when removing the hard mask film is performed using a phosphoric acid (H 3 PO 4 ).