Patent ID: 7846842

Claim:
A method of chemically-mechanically polishing a substrate comprising silicon nitride and silicon oxide, which method comprises: (i) contacting a substrate with a polishing pad and a chemical-mechanical polishing composition comprising: (a) a cationic abrasive, (b) a cationic polymer selected from the group consisting of (1) about 0. 1 ppm to about 50 ppm of a cationic homopolymer, (2) about 0.1 ppm to about 50 ppm of a cationic copolymer comprising at least one cationic monomer and at least one nonionic monomer, wherein the at least one cationic monomer comprises more than 50% of the cationic copolymer on a molar basis, and (3) about 0.1 ppm to about 200 ppm of a cationic copolymer comprising at least one cationic monomer and at least one nonionic monomer, wherein the at least one cationic monomer comprises 50% or less of the copolymer on a molar basis, and (c) water, wherein the polishing composition has a pH of about 7 or less, (ii) moving the polishing pad relative to the substrate with the chemical-mechanical polishing composition therebetween, and (iii) abrading at least a portion of the substrate to polish the substrate, wherein the silicon nitride is selectively removed in preference to the silicon oxide.