Research was performed to study the particle adhesion on the wafer surface after the chemical-mechanical polishing (CMP) process. The embedded particles can be abrasive particles from the slurry, debris from pad material, and particles of film being polished. Different methods of particle removal mechanism were investigated in order to find out the most effective technique. In post-CMP cleaning, surfactant was added in the solution. Results were compared with cleaning without surfactant and showed that cleaning was more effective with the combined interaction of the mechanical effort from the brush sweeping and the chemistry of the surfactant in the solution (i.e., tribochemical interaction). Numerical analysis was also performed to predict the particle removal rate with the addition of surfactants. The van der Waals forces present in the wafer-particle interface were calculated in order to find the energy required to remove the particle. Finally, the adhesion process was studied by modeling the van der Waals force as a function of separation distance between the particle and the surface. The successful adaptation of elasticity theory to nanoparticle-surface interaction brought insight into CMP cleaning mechanisms. The model tells us that it is not always the case that as the separation distance is decreased, the attraction force will be increased. The force value estimated can be used for slurry design and CMP process estimation.

Research was performed to study the particle adhesion on the wafer surface after the chemical-mechanical polishing (CMP) process. The embedded particles can be abrasive particles from the slurry, debris from pad material, and particles of film being polished. Different methods of particle removal mechanism were investigated in order to find out the most effective technique. In post-CMP cleaning, surfactant was added in the solution. Results were compared with cleaning without surfactant and showed that cleaning was more effective with the combined interaction of the mechanical effort from the brush sweeping and the chemistry of the surfactant in the solution (i.e., tribochemical interaction). Numerical analysis was also performed to predict the particle removal rate with the addition of surfactants. The van der Waals forces present in the wafer-particle interface were calculated in order to find the energy required to remove the particle. Finally, the adhesion process was studied by modeling the van der Waals force as a function of separation distance between the particle and the surface. The successful adaptation of elasticity theory to nanoparticle-surface interaction brought insight into CMP cleaning mechanisms. The model tells us that it is not always the case that as the separation distance is decreased, the attraction force will be increased. The force value estimated can be used for slurry design and CMP process estimation.

Many industrial processes involve powders in some form when making products, and the behavior of the powders processed is impacted by the adhesion of the individual particles which comprise it. This adhesion behavior, in turn, is critically influenced by the complementarity between the topography of a surface and the shape and roughness of the particles that adhere to that surface. Problems such as poor flowability, dust hazards, and equipment wear arise due to uncontrolled particle adhesion and can lead to production challenges. Computational models have been developed to predict the behavior of highly idealized powders (i.e., powders comprised of simple geometries such as spheres) under various processes but are limited in their ability to model and optimize the manufacturing and handling of powders comprised of many complex particles. This work focuses on further developing an experimental and modeling framework, called the Enhanced Centrifuge Method (ECM), that maps particle-scale and surface properties onto experimentally-validated ‘effective’ adhesion distributions that describe the adhesion between particles in powders. These distributions represent an engineering approach that allows powders comprised of particles of complex shape and roughness, which are challenging to model, to be described as if they were perfect, smooth spheres, which are comparatively simple to model. The complexity associated with the shape and size distributions of the individual particles is captured by the ‘effective’ adhesion parameters. These ‘effective’ adhesion parameter distributions provide a quantitative guide as to how the specific particle properties are interacting with the surface topography which directly impacts the overall powder adhesion. The initial framework of the ECM is constructed around characterizing the van der Waals adhesion of silica and polystyrene powders. The impact of the surface topography and the particle properties of each of the powders is captured in ‘effective’ Hamaker constant distributions. These distributions provide a quantitative guide for specifically how the particles interact with the surface topography based on the respective scales of the particle and surface features. The ECM framework is further adapted here to investigate the effects of topographical changes of stainless steel due to polishing on the adhesion properties of three different pharmaceutical powders to the stainless steel. In this adaptation of the ECM framework, the force of adhesion was described by modifying the Johnson, Kendall, and Roberts (JKR) model describing elastic-like particle contact to a flat plate. Within the modified JKR adhesion description, the work of adhesion is tuned to be an ‘effective’ work of adhesion parameter. These size-dependent ‘effective’ work of adhesion distributions provide a quantifiable measure of the change in the powder and surface adhesion that reflects the size, shape, and topographical features on the powder and surface with which the powder interacts. To investigate environmental effects on the adhesion properties, the ECM framework is also extended to characterize the effect humidity has on altering surface and particle interactions of the three pharmaceutical powders to stainless steel. In addition to the work with the pharmaceutical powders, the investigation of the effect of humidity on the powder’s adhesion includes a study of the influence of water on the interactions between silica particles and a silica substrate. In all cases, the ‘effective’ adhesion force distributions developed through the ECM provide the ability to quickly determine quantitatively how environmental and process conditions alter particle and surface properties, and overall powder behavior.

No description available.

This doctoral research was realized within the frame of the SMARTNET Project which aimed at developing coatings to improve the cleanability of stainless steel, targeting open surface applications. Throughout this thesis, the radial-flow cell was selected to study the removal of different soils due to its ability to generate well-controlled wall shear stress distributions on the investigated surfaces. Model surfaces were selected for their different physico-chemical and mechanical properties to study the interactions between the soils and the surfaces in detail. A thin layer chromatography sprayer giving a narrower and more reproducible droplet sizes distribution was preferred to mimic splashing and produce controlled spatters. The first experimental campaign involving oil droplets showed that the analytical models available to relate the detachment radius with the critical wall shear stress (minimal wall shear stress required for soil detachment) and the soil adhesion strength in the radial flow cell could only be applied for weakly adherent soils for which removal occurs below 3 Pa, due to the complex hydrodynamics near the inlet. Consequently, the flow inside the radial-flow cell has been characterized using computational fluid dynamics over the whole inlet laminar regime and validated experimentally. Studying the adherence of starch granule aggregates in the radial-flow cell revealed that the conversion of critical radius into critical wall shear stress may be biased when the adhering aggregate height is not negligible with respect to the channel height and when the adherence is such that flow rates above creeping flow conditions are required for soil detachment. The influence of several environmental factors and substrate properties was then examined to improve the understanding of the mechanisms affecting soiling and cleanability. By influencing droplet spreading and competition between capillary forces at the granule-substrate and granule-granule interfaces, substrate wettability affects the shape and compactness of the adhering aggregates, the efficiency of shear forces upon cleaning, and finally the adherence of soiling particles. Macromolecules originating from the starch granules suspension are adsorbed on the substrate from the liquid phase or carried by the retracting film and accumulated at the granule-substrate interface. They influence granule adherence by acting as an adhesive joint, the properties of which seem to be influenced by the detailed history of drying and exposure to humidity. On compliant substrates, the aggregate-substrate interactions induce stresses at the granule-substrate interface which may lead to substrate deformation and promote a more intimate contact between the granules and their substrate, thereby appreciably increasing adherence.

The adhesion and removal of particles from surfaces is a contemporary problem in many industrial applications like Semiconductor manufacturing, Bioaerosol removal, Pharmaceuticals, Adhesives and Petroleum industry. The complexity of the problem is due to the variety of factors like roughness, temperature, humidity, fluid medium etc. that affect pull-off of particles from surfaces. In particle removal from surfaces using fluid motion, the dynamic effects of particle separation will play an important role. Thus it is essential to study the dynamic effects of particle removal. Velocity of pull-off and force duration effects are two important dynamic factors that might affect pull-off. Particle adhesion studies can be made using the Atomic Force Microscope (AFM). The velocity of pull-off and force duration can be varied while making the AFM measurements. The objective of the current work is to obtain the dependence of pull-off force on pull-off velocity. Experiments were conducted using AFM and the data obtained from the experiments is processed to obtain plots for pull-off force vs. particle size and pull-off force vs. pull-off velocity. The pull-off force is compared with the predictions of previous contact adhesion theories. A velocity effect on pull-off force is observed from the experiments conducted.

Cyclopentane hydrate interparticle adhesion force measurements were performed in pure cyclopentane liquid using a micromechanical force apparatus. Cyclopentane hydrate adhesion force measurements were compared to those of cyclic ethers, tetrahydrofuran and ethylene oxide, which were suspected to be cyclic ether-lean and thus contain a second ice phase. This additional ice phase led to an over-prediction of the hydrate interparticle forces by the capillary bridge theory. The adhesion forces obtained for cyclopentane hydrate at atmospheric pressure over a temperature range from 274-279 K were lower than those obtained for the cyclic ethers at similar subcoolings from the formation temperature of the hydrate. The measured cyclopentane interparticle adhesion forces increased linearly with increasing temperature, and are on the same order of magnitude as those predicted by the Camargo and Palermo rheology model.

Colloidal particles suspended in a liquid or gas phase often interact with a solid-liquid or solid-gas interface. In this study, experimental data through atomic force microscopy and neutron reflectometry and theoretical results of colloidal particle-surface interactions were obtained and compared. Atmospheric and aquatic environments were considered for the interactions of microbial colloidal particles and nano-sized silica particles with planar surfaces. Spores of Bacillus thuringiensis, members of the Bacillus cereus group, were examined as the microbial particles, simulating the pathogens Bacillus cereus and Bacillus anthracis which are potentially dangerous to human health. Model planar surfaces used in this study include gold which is an electrically conductive surface, mica which is a highly charged, nonconductive surface, and silica. In atmospheric systems, the interaction forces were found to be strongly affected by the relative humidity, and the total adhesion force of a particle onto a surface was modeled as the addition of the capillary, van der Waals, and electrostatic forces. Each component is influenced by the properties of the particle and surface materials, including hydrophobicity and surface roughness, as well as the humidity of the surrounding atmosphere. In aquatic systems, the interaction forces are mainly affected by the solution chemistry, including pH and ionic strength. The main components of the interaction force between a microbial colloidal particle and a planar surface were found to be the van der Waals and electrostatic forces. The results obtained in this research provide insights into the fundamental mechanisms of colloidal particle interactions with environmental surfaces in both atmospheric and aquatic systems, contributing to the understanding of the phenomena driving such interfacial processes as deposition, aggregation, and sedimentation. Thus, the results can help us describe the behavior of contaminant colloidal particles in environmental systems and subsequently devise better means for their removal from environmental surfaces.