Pad roughness variation and its effect on material removal profile in ceria-based CMP slurry

The pad roughness plays a key role in material removal in oxide chemical mechanical polishing (CMP) process. Its variation also has an effect on within wafer non-uniformity. The Rpk among roughness parameters, which is related to pad wear characteristics, was investigated to find the correlation between spatial roughness distribution of a polishing pad, and material removal profile in CMP, using two different types of slurries. The removal rate of ceria-based slurry for STI CMP was higher in the wafer center than that of the silica-based slurry. This is because the pad roughness distribution in a convex shape is formed across the pad radius in the contact area between pad and wafer instead of the degradation of pad roughness during CMP. Also, there is an increase of Rpk results in the increase of average friction force by comparison with the decrease of friction force in CMP using silica-based slurry. This result may be expected as the effect of the chemical tooth of ceria abrasive and slurry accumulation in the wafer center causes a roughening of the pad surface just as sandpaper.