Settling of colloidal silica particles in CMP slurry: Monitoring, effect, and handling

The settling of colloidal silica particles in slurries results in changes of turbidity, specific gravity (SG), viscosity, particle size distribution (PSD), and concentrations of particle and chemical as a function of depth. Depending on the characteristics of slurry and mechanism of polishing, these changes may affect the removal rate. A container of slurry should be mixed properly before use in analysis and polishing to mitigate the effects from the settling of particles. Large particle count (LPC) is used as a sensitive method for monitoring the settling and re-dispersion of particles.