Experimental Studies on Interfacial Fluid Lubrication and Wafer Status during Chemical Mechanical Polishing of 12-inch Wafer

Abstract:
The mixed-lubrication is generated at the wafer-pad interface, and the wafer-pad interaction is very complex during CMP process. Therefore, it is very important to study and reveal the fluid lubrication behaviour and the wafer status during industrialized CMP process. In this study, the wafer status monitoring system is further developed for the integrated in-situ measurement system to monitor the wafer bending and the wafer orientation in addition with the fluid pressure during the dynamic polishing process. Using this in-situ measurement system, the fluid lubrication behaviour is studied for the CMP process of 12-inch wafer. The positive-dominated fluid pressure is observed, and the fluid pressure increases with the downforce. Furthermore, the wafer bending and the wafer orientation are studied using the in-situ measurement system. The results reveal that there exists a slightly convex wafer bending by the order of 10 µm and a positive pitch angle on the order of 10^-5~10^-4 degree under uniform downforce, and the wafer bending and pitch angle increase almost linearly with the downforce. The effects of the downforce on the wafer bending and the pitch angle are accordant with that on the fluid pressure, which indicates that the wafer bending and the wafer orientation play important roles in the hydrodynamic lubrication of CMP. Keywords: Chemical mechanical polishing, Fluid lubrication, In-situ measurement, Fluid pressure, Wafer orientation, Wafer bending