Hardness of submicrometre abrasive particles and polish rate measurements

Metal surfaces (copper and tantalum) and films (copper and tungsten) and silicon dioxide films were polished in deionised (DI) water using submicrometre sized alumina particles of varying density in benchtop Struers and Strasbaugh polishers. The polish rates for copper and tantalum in DI water increase significantly when the abrasive particle density exceeds a threshold value that correlates with the reported microhardness values of the (bulk) materials obtained using classical diamond pyramid microindentation measurements. Since it is expected that the density values are indicative of the particle hardness, this suggests, as might be expected, the existence of a threshold in the abrasive particle hardness for obtaining measurable polish rates. Based on this observation, the change in the relative hardness of thin films of copper exposed to two different chemical reagents in the chemical polishing of copper films was evaluated.