An Efficient and High Quality Chemical Mechanical Polishing Method for Copper Surface in 3D TSV Integration

The goal of chemical mechanical polishing (CMP) is to achieve a flat and smooth surface for through silicon via (TSV) application. In order to obtain high efficiency and high quality copper CMP process, we have developed copper CMP slurry with optimal component ratio of peroxide, citric acid, benzotriazole, and silica particle. A high-resolution surface profile measuring instrument combined with other measurements is used to analyze the CMP performance of TSV. In addition, the chemical reaction mechanism in slurry for removal copper has been discussed considering surface adsorption. It is revealed that the polishing time increases with decreasing content of oxidizing agent peroxide. The polishing speed for silica particle mixed slurry is accelerated comparing with the conventional slurry. The polishing time becomes longer with increasing value of pH owing to declining sharply of free hydrogen ion in slurry solution. Further, the high quality of polishing appears on the wafer with smooth and glossy surface of copper by applying fast and slow slurry, which is contributed to reduction of the chemical polishing and enhancement of the mechanical polishing. The optimized polishing slurry prepared in this paper and the proposed two-stage polishing technique can achieve high quality copper surface polishing while greatly improving polishing efficiency.