A composition for polishing silicon nitride according to the present invention includes colloidal silica, a polishing aid including a phosphoric acid compound and a sulfuric acid compound. By further including an oxidizing agent, a first selectivity representing the ratio of a polishing speed for a metal layer to a polishing speed for a silicon nitride layer and a second selectivity representing the ratio of a polishing speed for an oxide insulating layer to a polishing speed for a silicon nitride are controlled.
