Effective filtration of chemical mechanical planarization slurries

Low abrasive content and much smaller mean particles of silica, alumina and ceria abrasives in new generation chemical mechanical planarization (CMP) slurries demand much tighter retention of ≥0.5 μm and even smaller particles with least effect on the mean working particles. Current slurry manufacturing processes target 90% and higher reduction of cumulative large particle counts (LPCs) at ≥0.56 or 1.01 μm in a single pass. Filtration using graded density, multiple thin-layer, and pleated depth filter media or membranes can provide needed retention depending on the slurry characteristics. Efficient slurry filter design must consider slurry abrasive type and morphology, LPCs, mean particle size distribution (PSD), wt% solids, oxidizers, chemicals and organic additives, blending protocols, viscosity, abrasive settling rate, target retention level, pressure drop (Δp) limits, flow rate stability and expected filter lifetime. Results of retention, flow rate and Δp from filtration tests using 0.50 and 1.0 μm nominal rating depth media samples show very different behavior in silica, alumina and ceria slurries, confirming that newer CMP slurries filter optimization still remains empirical in nature. This study shows that laboratory and field characterizations, and post-use filter analysis are useful in filter optimization. This study demonstrates that the filtration of newer CMP slurries is useful in managing large particles.