Mathematical modeling of CMP conditioning process

Up to now, the conditioning model with an oscillating conditioner wheel has not been studied. In this paper, kinematic analysis of the conditioning process and mathematical modeling of pad wear while the conditioner wheel oscillates is studied and the results show how the various parameters of the conditioning process influence the pad shape. The conditioning of the polishing pad is one of the most important processes associated with the CMP (Chemical Mechanical Polishing). As the wafer is polished, the surface of the pad can be deteriorated with a reduced polishing rate and reduced planarity due to wear and glazing of the pad. Thus, the polishing pad needs to be conditioned to maintain its effectiveness. In general, the conditioning process is used to regenerate the pad surface by breaking the glazed area of the pad and increase the MRR (Material Removal Rate) and give us longer pad life. However, as the conditioning process continues, the pad shape becomes more and more concave over the whole pad while the conditioner wheel oscillates (Y.Y. Zhou, E.C. Davis, Mat. Sci. Eng. B. 68 (1999), 91–98). It has been shown that the concavity of the polishing pad increases with conditioning time – longer conditioning induces a higher incidence of concavity of the polishing pad. Therefore, the conditioning process is related to the WIWNU (Within Wafer Non-Uniformity). Through this conditioning model, thickness variation of the polishing pad can be predicted.