Silica-based slurry for selective polishing of silicon nitride and silicon carbide

A method of chemically-mechanically polishing a substrate comprising:

• providing a substrate, wherein the substrate comprises silicon nitride on a surface of the substrate;
• providing a polishing pad;
• providing a chemical-mechanical polishing composition comprising:
• (a) about 0.001 wt. % to about 10 wt. % of a silica abrasive;
• (b) about 0.05 wt. % to about 2 wt. % of a buffering agent;
• and
• (c) water,
• wherein the polishing composition has a pH of about 1 to about 7 and the silica abrasive has a zeta potential of about −10 mV to about −50 mV in the polishing composition, and wherein the silica abrasive is not doped with a metal;
• contacting the substrate with the polishing pad and the chemical-mechanical polishing composition;
• and
• moving the polishing pad and the chemical-mechanical polishing composition relative to the substrate to abrade at least a portion of the substrate to polish the substrate.