Slurry compositions for selectively polishing silicon nitride relative to silicon oxide, methods of polishing a silicon nitride layer and methods of manufacturing a semiconductor device using the same

Slurry compositions for selectively polishing silicon nitride relative to silicon oxide, methods of polishing a silicon nitride layer and methods of manufacturing a semiconductor device using the same are provided. The slurry compositions include a first agent for reducing an oxide polishing rate, an abrasive particle and water, and the first agent includes poly(acrylic acid). The slurry composition may have a high polishing selectivity of silicon nitride relative to silicon oxide to be employed in selectively polishing a silicon nitride layer in a semiconductor manufacturing process.