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

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.