Dispersion stabilization of carbonyl iron particles and its applications in chemical mechanical planarization

Abstract

A novel aqueous magnetorheological (MR) slurry is proposed for potential application in the planarization of dielectric substrates, eliminating the need for traditional polishing pads. The preparation of a stable MR slurry hinges on the dispersion properties of abrasives and magnetic responsive particles, particularly high-density carbonyl iron particles (CIP). This study focuses on investigating the dispersion stabilities of CIP and its modified form, SiO2-coated CIP (SiO2@CIP), with the addition of ammonium polyacrylic acid (PAA-NH4) as a dispersant. Experimental measurements, including adsorption isotherms and zeta potential, combined with numerical simulations using density-functional theory, explore the adsorption behavior of PAA-NH4 on CIP and SiO2@CIP. Rheological and sedimentation analyses confirm PAA-NH4’s effectiveness in dispersing both particles. We elucidate the dispersion stabilization mechanism through calculations based on the Derjaguin−Landau−Verwey−Overbeek theory. In MR polishing, SiO2 coating on CIP improves efficiency, reducing surface roughness from over 8 nm (using CIP) to less than 8 Å (using SiO2@CIP). The addition of PAA-NH4 augments dispersion properties, leading to further enhancements in polishing efficiency, resulting in a surface roughness reduction to 2 Å and a simultaneous increase in material removal rate. We thoroughly examine the underlying factors driving these improvements.