Facts
Mechanical stress can impact CMP slurries used in wafer planarization processes. Shear stress in pumps, used in delivery and CMP tools, can cause changes to the particle size distribution due to slurry agglomeration. Particle agglomerates cause wafer defects but also limit the life of filters.

Test conditions
The Levitronix^® BPS-200 and BPS-600 pumps were evaluated for their effect on the health of Cabot Semi-Sperse^® 12 slurry. The BPS-200 pump was used to circulate of slurry at 4.8 lpm and 2.1 bar, while the BPS-600 pump was used to circulate slurry at 30 lpm and 2.1 bar. Samples were drawn from the system at selected times for analysis. The particle size distribution of each sample was measured and the concentration of each particle size was compared to the initial concentration.

Results
No relevant increase in the concentration of particles in the large particle tail was observed during either pump test. Rather, the concentration of large particles actually decreased during the BPS-200 pump test. This effect increased as particle size increased. Meanwhile, no measurable change in the concentration of large particles occurred during the BPS-600 pump test.
Little change in the working PSDs was observed. A slight increase (≤ 5%) in the 99th percentile particle size was observed after 1,000 turnovers during the BPS-200 and BPS-600 pump tests, respectively.

Particle concentrations relative to the initial concentration for selected size channels with the BPS-200

Particle concentrations relative to the initial concentration for selected size channels with the BPS-600