Size distribution monitoring for chemical mechanical polishing slurries: An intercomparison of electron microscopy, dynamic light scattering, and differential mobility analysis

In chemical mechanical planarization (CMP), a particle slurry is used in polishing semiconductor wafers. Key to its performance is the size distribution of the particles. We evaluate the potential of an aerosol technique, namely differential mobility analysis (in a liquid nanoparticle sizer, LNS, system) to characterize size distributions of CMP slurries. LNS measurements are compared to size distributions inferred from electron microscopy (SEM), and dynamic light scattering (DLS). LNS measurements are more repeatable than DLS measurements, and for 4 silica slurries, LNS distributions are in better agreement with SEM measurements than DLS. We find also that the LNS can quantify multimodal size distributions. For non-silica slurries, LNS, DLS, and SEM measurements have geometric mean diameters which can vary from another by 10 nm or more. However, because each measurement type is internally consistent, the combination of LNS and DLS, which are automated, yields augmented information on slurry properties.