Analysis of the Tribological Mechanisms Arising in the Chemical Mechanical Polishing of Copper-Film Wafers

Abstract

In the chemical mechanical planarization of a copper-film silicon wafer, the average Reynolds equation with flow factors has also been developed for a cylindrical coordinate system to study the mixed lubrication. The pad’s elastic deformations are considered in the evaluation of the contact pressure arising at the interface of a pad’s asperity and the wafer. The normal force acting on the wafer by an abrasive particle is thus obtained in order to calculate the elastic and plastic deformations of the copper film with a thin passivation layer. A theoretical abrasive wear model is developed to evaluate the removal rate of the copper film. The increase in the real contact area of an abrasive, due to the frictional force produced at the interface by adhesive wear, is also taken into account. A nano tester was applied to measure the composite hardness and Young’s modulus of the copper-film wafer with a passivation layer. These two material properties are of importance in the calculation of wafer’s theoretical removal rate. Experimental results for the removal rates of the copper film are exhibited to compare with that predicted by the present theoretical model. Fairly good agreement exists in the trends of the removal rates varying in the radial direction and the mean removal rates evaluated at different operating conditions.