# Flow-Induced Dynamic Dispersion in Dispersant-Free Mixed-Oxide Slurry Systems

## TL;DR

This study shows that mixing different-sized silica particles improves slurry performance in planarization better than chemical dispersants.

## Contribution

A particle-mixing strategy outperforms chemical dispersants in dynamic dispersion and CMP performance.

## Key findings

- Bimodal suspensions show nearly Newtonian flow behavior and suppress agglomeration.
- CMP tests show higher material removal rates and lower surface roughness with bimodal suspensions.
- Simulations reveal denser particle contacts and higher stresses in bimodal systems.

## Abstract

This study demonstrates that a particle-mixing strategy
in aqueous
suspension is more effective than chemical dispersants in enhancing
the dynamic dispersion and performance of SiO2-based slurries
for planarization applications. By preparing particle-mixed suspensions
containing 25 and 55 nm SiO2 particles at chemical-mechanical
planarization (CMP)-relevant solid loadings (1–10 wt %), we
show that combining these two particle sizes suppresses agglomeration
and transforms the suspension rheology from shear-thinning to a nearly
Newtonian response under flow, indicating improved dynamic dispersion
after yielding. Small-angle X-ray scattering and effective volume
packing analyses confirm that cooperative size effects drive the improved
structural organization, thereby enhancing flow behavior. In contrast,
the commonly used ammonium polyacrylate dispersant enhances static
dispersion but fails to produce uniform flow behavior under shear.
In CMP tests, suspensions with a bimodal particle size distribution
achieve higher material removal rates and lower surface roughness
than monodisperse or dispersant-stabilized suspensions simultaneously.
Numerical simulations that couple the discrete element method and
computational fluid dynamics further show that the improved CMP performance,
resulting from the use of the powder-mixing suspension, is due to
denser particle contacts and higher localized stresses in the bimodal
system.