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

A method of manufacturing a semiconductor device comprising:

• forming a first silicon nitride layer pattern on a substrate to have a length extending along the substrate in a first direction;
• partially etching the substrate using the first silicon nitride layer pattern as an etching mask to form a trench at an upper portion of the substrate;
• forming a silicon oxide layer to fill the trench and to define an active region of the substrate;
• removing a portion of the silicon oxide layer adjacent to both ends of the active region in the first direction to form a recess in the silicon oxide layer;
• forming a second silicon nitride layer on the first silicon nitride layer pattern and the silicon oxide layer to fill the recess;
• and
• polishing the second silicon nitride layer using a slurry composition until the silicon oxide layer is exposed to form a second silicon nitride layer pattern that fills the recess, the slurry composition including a first agent for reducing an oxide polishing rate, an abrasive particle and water, the first agent including poly(acrylic acid).