Yakov I. Rabinovich

Capillary forces between surfaces with nanoscale roughness

The flow and adhesion behavior of fine powders (approx. less than 10 microm) is significantly affected by the magnitude of attractive interparticle forces. Hence, the relative humidity and magnitude of capillary forces are critical parameters in the processing of these materials. In this investigation, approximate theoretical formulae are developed to predict the magnitude and onset of capillary adhesion between a smooth adhering particle and a surface with roughness on the nanometer scale. Experimental adhesion values between a variety of surfaces are measured via atomic force microscopy and are found to validate theoretical predictions.

Role of surface roughness in capillary adhesion

The adhesion forces between a smooth spherical particle and flat surfaces of alumina, silver, and titanium-coated Si wafers were measured with an atomic force microscope (AFM) under various humidity conditions. The results showed that there is a discrepancy between the experimentally observed and the theoretically predicted values of capillary adhesion forces. The reason for the discrepancy is explained considering the relative humidity of the surrounding atmosphere and the surface roughness profiles of the contacting surfaces. Two geometrical configurations to define the contact region profile are suggested. The equations to calculate the capillary adhesion forces were modified using the new geometries. The discrepancy was largely eliminated using the modified equations.

Measurement of oil-mediated particle adhesion to a silica substrate by atomic force microscopy

Preventing particle segregation while maintaining flow is critical to enable processing in a variety of industries. Where segregation or dusting is particularly troublesome, oil may be added to the powder to increase cohesion between particles or to attach flow-aids to the particle surface. In this investigation, the role of the capillary force produced by an oil annulus between surfaces and its influence on adhesion are explored. The results of direct measurement by atomic force microscopy are compared with ensemble powder properties, as well as a simple theoretical expression that predicts the magnitude of the adhesion force as a function of the separation distance. Agreement is achieved between theory and experimental data using only the volume of the oil annulus and its surface tension as variables.

Impact of Pad–Wafer Contact Area in Chemical Mechanical Polishing

Chemical mechanical polishing (CMP) is widely adopted in producing excellent local and global planarization of microelectronic devices. However, the fundamental mechanisms of material removal and the interactions of the chemical and mechanical effects are not well understood. In the present paper, the contact area of a pad with a wafer is measured in dry and wet conditions in different pH solutions using optical microscopy and Fourier transform infrared spectroscopy, respectively. Pad surface mechanical properties in dry and wet states are also investigated using atomic force microscopy. The results indicate a significant difference in pad surface mechanical properties between dry and wet states, which could be correlated with the CMP removal rates.

Surface interaction forces in chemical-mechanical planarization

Abstract Understanding the role of surface intra-molecular forces is critical in a variety of aspects of chemical-mechanical polishing technology. In this paper we explore some of the critical areas where this is an important parameter, such as material removal mechanisms in oxide polishing. Particular attention is given to the use of coupling single particle atomic force microscopy experiments with FTIR and TEM studies of polished oxide surfaces in studying the possible role of surface hydration effects in chemical-mechanical planarization of oxide thin films.

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 (Ca(2+)) addition on dodecyl trimethylammonium bromide (C(12)TAB) 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.

Interaction force measurements using atomic force microscopy for characterization and control of adhesion, dispersion and lubrication in particulate systems

Atomic force microscopy is used as a vital tool in understanding the fundamental mechanisms of particulate processes in dry, humid and aqueous systems. Adhesion forces in both dry and humid systems were studied between surfaces of varying roughness, taking into account the capillary forces at high humidity conditions. Colloidal stability in aqueous systems due to non-DLVO forces and steric effects of surfactant aggregates formed on particle surfaces at varying pH and ionic strength conditions were investigated. The force–distance curves obtained by atomic force microscopy were used to determine the mechanical and thermodynamic properties of the self-assembled surfactant structures formed on the surface. Besides determining the repulsive force barrier provided by the surfactant aggregates in dispersion of slurries, the frictional interactions between surfactant adsorbed surfaces were measured using lateral force microscopy, providing valuable insights into the role of dispersants acting as lubricants. The range of interaction forces that can be explored using the Atomic Force Microscopy (AFM) can be utilized to predict, optimize and design a variety of industrially relevant processes such as chemical mechanical polishing (CMP), powder flow and handling and nano-dispersions, just to name a few.

Role of Capillary Forces in the Reduction of Dust Pollution During Transport and Handling of Powders

Mixing of dry powders with oil or liquid binder is often done to minimize segregation and dust pollution during handling and transport. The amount of binder required is determined empirically due to inadequate models. Oil as a binder forms capillary bridges between particles. In the present study, theoretical expressions are developed for the calculation of the capillary force at different oil interlayer thickness between particles. Experimental measurements using AFM were conducted to validate the theory for particle/particle and particle/wall interactions.