Electrochemically induced defects during post Cu CMP cleaning

The electrochemical properties of various cleaning reagents of high, medium or low pH values for post Cu CMP cleaning and their interaction mechanisms with Cu surfaces were studied. Results showed that for the Cu in TMAH (pH=11) a reverse reaction, Cu re-deposition, was also observed although the Cu was easier to corrode due to its more negative corrosion potential in this solution. Because of this abnormal Cu re-deposition, Cu anode and cathode reactions were found to occur at the same Cu islands, where the Cu were corroded and then re-filled by re-deposition to form allow defects. These defects were extremely difficult to detect by in-line defect inspection tools during wafer processing and can only be identified by FA after WAT failures. Careful examinations of electrochemical properties revealed that hump in the I-V curve is the key to this abnormalities and a novel solution was proposed and developed to eliminate these defects.