Method For The Preferential Polishing Of Silicon Nitride Versus Silicon Oxide
The present invention provides a method of removing silicon nitride in preference to silicon dioxide by CMP. The method utilizes a polishing slurry that includes colloidal silica abrasive particles dispersed in water and an additive that suppresses the silicon dioxide removal rate but enhances the silicon nitride removal rate. In one embodiment of the invention, the additive is lysine, which is effective at a pH of about 9, or arginine, which is effective at a pH of about 8. In another embodiment of the invention, the additive is lysine mono hydrochloride in combination with picolinic acid, which is effective at a pH of about 8, or arginine in combination with picolinic acid, which is effective at a pH of about 9.
1 - 7 . (canceled)
8 . A method for removing silicon nitride from a surface at a greater rate than silicon dioxide is removed from the surface, the method comprising:
a) providing a polishing slurry having a pH of about 9±0.5, said polishing slurry comprising colloidal silica abrasive particles dispersed in water together with an additive comprising a first compound and a second compound, wherein said first compound comprises an organic compound containing an alpha-amino acid functional group and a guanidine group and said second compound comprises picolinic acid or a derivative thereof;
b) disposing the polishing slurry between a polishing pad and the surface; and
c) pressing the polishing pad against the surface while the polishing pad and surface are moving relative to each other with the polishing slurry disposed therebetween to remove silicon nitride from the surface at a greater rate than silicon dioxide is removed from the surface.
9 . The method according to claim 8 wherein said first compound comprises arginine.
10 . (canceled)
11 . The method according to claim 8 wherein the polishing slurry comprises from about 5% to about 15% by weight of silica particles having a mean average diameter of from about 25 nm to about 75 nm.
12 . The method according to claim 8 wherein the polishing slurry comprises from about 1.0% to about 4.0% by weight of said first compound.
13 . The method according to claim 9 wherein the polishing slurry comprises about 10% by weight of silica particles having a mean average diameter of about 50 nm and from about 1% to about 3% by weight of arginine.
14 . The method according to claim 8 wherein the polishing slurry comprises from about 1.0% to about 3.0% by weight of picolinic acid.
15 - 19 . (canceled)