A chemical mechanical polishing slurry for polishing a copper layer without excessively or destructively polishing a barrier layer beneath the copper layer is disclosed and includes an acid, a surfactant, and a silica sol having silica polishing particles that are surface modified with a surface charge modifier and that have potassium ions attached thereto. A method for preparing the chemical mechanical polishing slurry and a chemical mechanical polishing method using the chemical mechanical polishing slurry are also disclosed.