Lateral force microscopy study of the friction between silica surfaces in electrolyte solutions

Lateral force measurements between a polished silica wafer and a colloidal silica particle in monovalent electrolyte solution environment (LiCl, NaCl, CsCl) were performed using an Atomic Force Microscope (AFM). Analysis of the friction versus load data, in LiCl case, indicates that increasing the electrolyte concentration, the intensity of the friction force decreases. The effects of the counterions on lateral forces show that friction coefficients gradually decrease from pure Dl water to 1.0M LiCl. Lateral forces versus scan rate graphs show a typical behavior for all investigated systems: transition and saturation region. These results are consistent with the idea that strongly hydrated ions have a lubrication effect in silica-silica interactions

Studies on slurry design fundamentals for advanced CMP applications

Due to copyright restrictions, the access to the full text of this article is only available via subscription.New developments and device performance requirements in microelectronics industry add to the challenges in chemical mechanical planarization (CMP) process. One of the recently introduced materials is germanium which enables improved performance through better channel mobility in shallow trench isolation (STI) applications. This paper reports on the slurry design alternatives for Ge CMP with surfactant mediation to improve on the silica/germanium selectivity using colloidal silica slurry. In addition to the standard CMP tests to evaluate the material removal rates, atomic force microscopy (AFM) based wear tests were also conducted to evaluate single particle-surface interaction of the polishing system. Furthermore, nature of the surface oxide film of germanium was studied through contact angle measurements and surface roughness tested by AFM. It was observed that the CMP selectivity of the silica/germanium system and defectivity control were possible with a reasonable material removal rate value by using self-assembled structures of cationic surfactants

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

Due to copyright restrictions, the access to the full text of this article is only available via subscription.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