A Model for Effect of Colloidal Forces on Chemical Mechanical Polishing

It is well known that the variation of slurry pH could significantly affect the chemical-mechanical polishing (CMP) process. In this study, a particle-scale mechanical model for surface removal rate that includes the double layer (dl) forces of abrasives and wafer surface is developed. It is shown that the van der Waals force and the electrical dl attraction and repulsion play a major role in CMP processes. Furthermore, the magnitudes and signs of the zeta potential of the surface and the abrasives significantly affect the removal rates. The results show that the removal rate increases sharply for the cases that the zeta potentials of the surface and abrasive have opposite sign. On the other hand the removal rate decreases when the zeta potentials have the same sign. The removal rates for polishing of tantalum with silica and alumina abrasives are compared with the available data and qualitative agreements are observed.