Facts
In comparison to Levitronix^® pumps, pneumatic pumps can cause shear stress due to check valves and other components. Shear stress in pumps can cause slurry agglomeration. Agglomerated slurry particles can lead to micro scratches causing wafer defectivity in CMP.

Test conditions
A Levitronix^® BPS-4 pump, a diaphragm pump, and a bellows pump were evaluated for their effect on the health of Cabot Semi-Sperse^® 12 slurry. A fixed volume of slurry was recirculated at 30 lpm and 2.1 bar, and samples were drawn from the system at selected times for analysis. The particle size distribution of each sample was measured and the increase in particle concentration relative to the initial concentration was compared.

Results
Little change in the particle size distribution was observed with Levitronix^® pumps, regardless of particle size. With bellows and diaphragm pumps, significant increases particularly in the large particle concentrations were observed.

Effect of pumps on particles ≥ 0.56 µm (linear scales)