Molybdenum Ion-Induced Adhesion of Colloidal Silica to Polyvinyl Acetal Brushes in Post-Chemical Mechanical Planarization Applications: Experiments and Multiscale Simulations

The pH-dependent effect of molybdenum (Mo) ions on the interfacial interactions governing colloidal silica particle loading onto poly(vinyl acetal) (PVAc) brushes during post-CMP cleaning was explored. Initially, colloidal silica particles are proposed to interact with Mo ions to form Si-O-Mo linkages, and the resulting complexes subsequently adsorb onto the PVAc brushes. The presence of Mo ions increased the loading of colloidal silica particles onto the PVAc brush under acidic pH conditions. The particle loading onto the PVAc brushes was highest at pH 3 and decreased with increasing pH due to enhanced electrostatic repulsion, as supported by zeta potential measurements and FE-SEM analyses. Furthermore, with increasing Mo ion concentrations, the amount of Mo ions loaded onto the silica particles increased, as measured via ICP-AES (0.06 to 4.3 ppm). XPS analysis revealed that Mo₂O₅ was the dominant species, followed by MoO₂ and MoO₃, which interact with colloidal silica particles at pH 3, where the PVAc brush loading was highest. FT-IR analysis showed that a distinct band at ∼949 cm^-1 is consistent with the formation of Si-O-Mo interfacial bonds between Mo species and surface silanol groups. In addition, the presence of the O-Mo RDF peak near ∼2.65 Å supports a well-defined Mo-O coordination at the interface. Molecular dynamics simulations revealed that hydroxide-ion diffusivity increased with an increasing protonated Mo₂O₅ content in the colloidal silica system, enhancing interactions with PVAc brushes. Density functional theory further confirmed strong interactions among silica particles, Mo oxides, and PVAc through quantum chemical parameters such as electrostatic potential, HOMO, and LUMO.