Tailoring silica nanotribology for CMP slurry optimization: Ca²⁺ cation competition in C₁₂TAB mediated lubrication

Self-assembled surfactant structures at the solid/liquid interface have been shown to act as nanoparticulate dispersants and are capable of providing a highly effective, self-healing boundary lubrication layer in aqueous environments. However, in some cases in particular, chemical mechanical planarization (CMP) applications the lubrication imparted by self-assembled surfactant dispersants can be too strong, resulting in undesirably low levels of wear or friction disabling material removal. In the present investigation, the influence of calcium cation (Ca²⁺) addition on dodecyl trimethylammonium bromide (C₁₂TAB) mediated lubrication of silica surfaces is examined via normal and lateral atomic force microscopy (AFM/LFM), benchtop polishing experiments and surface adsorption characterization methods. It is demonstrated that the introduction of competitively adsorbing cations that modulate the surfactant headgroup surface affinity can be used to tune friction and wear without compromising dispersion stability. These self-healing, reversible, and tunable tribological systems are expected to lead to the development of smart surfactant-based aqueous lubrication schemes, which include designer polishing slurries and devices that take advantage of pressure-gated friction response phenomena.