As semiconductor scaling advances, tolerances for Chemical Mechanical Planarization (CMP) defectivity become increasingly strict. CMP relies heavily on the colloidal stability of slurries, which depends on a delicate balance of repulsive and attractive forces. During distribution, mechanical handling can overcome repulsive electrostatic barriers, causing particles to agglomerate. Preventing the growth of the overall Particle Size Distribution (PSD) “tail” (particles > 1 µm) is critical, as these oversized aggregates cause severe mechanical defects like micro-scratches that reduce manufacturing yield. Proper selection of slurry handling equipment is therefore vital to maintain baseline PSDs and minimize defectivity.

Historically, slow-moving bellows and diaphragm pumps were favored for slurry delivery as perceived “low shear” devices, while high-speed centrifugal pumps were avoided due to shear concerns. To assess the validity of this assumption, continuous circulation tests compared the effects of bellows, diaphragm, and magnetically levitated (maglev) centrifugal pumps on slurry health. Nine commercial CMP slurries (fumed/colloidal silica, alumina, and ceria) were circulated for up to 1,000 tank turn- overs, and their PSDs were continuously monitored.

During this study, it was found that circulation with bellows and diaphragm pumps caused rapid, significant increases in large particle concentrations (≥ 0.56 µm), often multiplying 20 to 70 times over 1,000 turnovers. Conversely, the maglev centrifugal pump caused minimal to no increase in the large particle tail across abrasive types. In some cases, the maglev pump’s moderate shear beneficially broke apart loose agglomerates.

Further testing was conducted to isolate the effects of fluid shear from cavitation by running a mag-lev pump at a constant speed while varying inlet pressure. Results demonstrated that shear alone does not damage the slurry; instead, the violent collapse of bubbles during cavitation is the primary mechanism causing particle agglomeration. Volumetric pumps inherently generate high cavitation probabilities during suction and within check valves, causing the observed PSD degradation.
This presentation will review the results of these, and other studies conducted to assess the impact of slurry handling components on slurry health.