In a damascene process for a copper metallization, the planarization method based on a chemical mechanical polishing (CMP) has been used for multilevel metallization. Although a buffing step was adopted in this CMP process, numerous residual abrasives, capable of increasing the resistance of copper lines, still existed after the second CMP step. For this reason, more research has focused on identification of an effective cleaning solution. We investigated a new cleaning solution consisting of citric acid and 5-aminotetrazole (ATRA) as a complexing agent and corrosion inhibitor, respectively. The citric acid was added to achieve a lift-off effect by removing the underlying copper oxide layer, whereas the ATRA was adopted to prevent abrasive re-adsorption by forming a passivation layer on the copper surface. The cleaning solution consisting of 0.006M citric acid and 0.006M ATRA displayed a particle density of 0.07 #/μm2 in an immersion test, and no particles were observed on a 4 cm2 coupon wafer in a real process test at pH 12.