Dynamical Mechanism of Chemical Mechanical Polishing Analyzed to Correct Preston’s Empirical Model

The dynamical mechanism of chemical mechanical polishing (CMP) is described. The relationships between removal rate and CMP parameters were evaluated by directly measuring the frictional force acting on a wafer under actual CMP conditions. According to the evaluation using various types of slurries, we devised a new relationship to replace Preston's empirical equation by taking into account the dynamic frictional coefficient and the polishing efficiency. The quantitative analysis revealed that the removal rate was proportional to frictional force rather than down force, and the dynamic frictional coefficient and the polishing efficiency remain constant by the change of the down force. The change of removal rate by the sliding speed is varied depending on the kind of slurries. The polishing efficiency tends to be degraded by the increase of the sliding speed, while the dynamic frictional coefficient can either increase or decrease depending on the slurries. This suggests that the CMP mechanism changes by the sliding speed.