Abstract
Knowledge of the defect behaviors of copper-interconnect surface is important for continuous yield improvement. This study is to focus on the defect behavior in copper damascene process, aiming at, (a) pits-formation mechanism related to structure and impurities of deposits during polishing (b) extrusion-formation mechanism for copper oxidation and light illumination after polishing.First, we investigate the effect of current density and impurities incorporated in blanket and pattern wafer by potentiodynamic polarization method, X-ray diffraction and secondary ion mass spectroscopy. Defect count is decided by optical scan method and SEM reviewing. Removal rate and corroded pits are found to decrease with increasing (111)/(200) ratio because (111), the closed packed plane of the fcc structure, has strong chemical resistance during polishing. Furthermore, incorporated impurities, such as carbon, chloride and sulfur, tend to weaken grain boundaries to generate more corroded pits, but do not affect removal rate. In addition, geometric constraint induces concentrated impurities to restrict copper grain growth and induce fast oxide growth rate, resulting in large dishing effect on the wafer.Second, copper-extrusion defect is initiated at grain boundary on interconnect surface and its size is enlarged with time and finally reaches a fixed value over a period of time after chemical mechanical polishing. The extrusion is composed of derivatives of copper oxide, not being observed under nitrogen environment, and increases with time after polishing. Auger analysis was used to compare the impure atoms between locations with and without extrusion, which proves that impurity is an important factor for initial growth. It has been verified that growth rate of copper-oxide extrusion increases with increasing impurity content of the copper deposit. Moreover, illumination significantly enhances and accelerates the growth rate of copper-oxide at the initial nucleation stage by providing more electron carriers and acceptors. It has also been discovered that illumination effect is related to impurities of grain boundaries, which need to be sufficiently enhanced by illumination to generate nucleation sites.