Localized Oxidation of the Cu Surface after Chemical Mechanical Planarization Processing

Abstract

After chemical mechanical planarization (CMP) processing of a Cu/low- k structure device, defects are often observed and some of them induce problems in manufacturing very large scale integrated circuit (VLSI) devices. As an example of defects, watermarks and protrusions on the Cu are detected. We found that the number of watermarks or protrusions is strongly affected by the cleaning conditions. The energy dispersive X-ray analysis (EDX) showed that these protrusions were composed of Cu and O. Moreover, atomic force microscopy (AFM) observations revealed that these protrusions grew during the storage time after the postcleaning. Electrochemical measurements also indicated that the protrusions were oxidized copper formed in the cleaning solutions due to the difference in corrosion current densities for various conditions of the Cu surface. Therefore, optimization of the post-CMP cleaning processing is a key issue for the reduction of defects such as protrusions.