The present invention provides aqueous CMP polishing compositions comprising a from 0.5 to 30 wt. %, based on the total weight of the composition of a dispersion of a plurality of elongated, bent or nodular colloidal silica particles which contain a cationic nitrogen atom, and from 0.001 to 0.5 wt. %, preferably from 10 to 500 ppm, of a cationic copolymer of a diallyldimethylammonium salt, such as a diallyldimethylammonium halide, wherein the compositions have a pH of from 1 to 4.5. Preferably, the cationic copolymer of a diallyldimethylammonium salt comprises a copolymer of diallyldimethylammonium chloride (DADMAC) and sulfur dioxide. The slurry compositions demonstrate good oxide selectivity in the CMP polishing of pattern wafers having nitride and silicon patterns.