A chemical mechanical polishing slurry includes an additive of a quaternary ammonium compound having a form of {N—(R1R2R3R4)}+X−, in which R1, R2, R3, and R4 are radicals, and X− is an anion derivative including halogen elements. Preferably, the quaternary ammonium compound is one of [(CH3)3NCH2CH2OH]Cl, [(CH3)3NCH2CH2OH]l, [(CH3)3NCH2CH2OH]Br, [(CH3)3NCH2CH2OH]CO3, and mixtures thereof. The slurry may further include a pH control agent formed of a base such as KOH, NH4OH, and (CH3)4NOH, and an acid such as HCl, H2SO4, H3PO4, and HNO3. Also, the pH control agent can include [(CH3)3NCH2CH2OH]OH. The slurry may further include a surfactant such as cetyldimethyl ammonium bromide, cetyldimethyl ammonium bromide, polyethylene oxide, polyethylene alcohol or polyethylene glycol.