Copper chemical mechanical polishing using a slurry-free technique

A study of the chemical mechanical polishing (CMP) of thin copper films using fixed-abrasive pads is presented. The composition of the polishing solution is optimized by investigating the impact of both the oxidizer concentration and the pH of the solution on the polishing characteristics of copper. The resulting optimum polishing solution gives a high removal rate (>300 nm/min), good uniformity (standard deviation 3%) and a very high selectivity for the oxide removal rate (>100:1). The dependence of the removal rate of copper on the geometry is studied for different feature sizes and various pattern densities. The geometry dependency is considerably less in the slurry-free process than in the conventional slurry CMP. This is crucial for copper CMP because it helps to minimize the overpolishing time and consequently the amount of dishing. Damascene copper structures have been successfully made by polishing patterned test wafers. The amount of dishing of the copper lines is smaller than that for the conventional polishing technique. The polished wafers were easily cleaned; a standard rinsing step seemed to be sufficient.