Jakub Nalaskowski

Chemical Mechanical Planarization: Slurry Chemistry, Materials, and Mechanisms

3. FEOL Applications: Device Level 180 3.1. Shallow Trench Isolation (STI) CMP 180 3.2. Replacement Metal Gate CMP 184 3.3. Poly-Si CMP for FinFET Devices 186 4. MOL Applications: Contact Level 187 4.1. Tungsten CMP 187 5. BEOL Applications: Multilevel Interconnects 188 5.1. Copper Interconnect Technology 188 5.2. CMP Challenges in Cu Interconnects 189 5.2.1. Low-k and Ultralow-k Material Challenges 189 5.2.2. Integration Challenges 190 5.2.3. CMP Process Challenges 191 5.3. Copper Planarizarion Process 191 5.4. Ta/TaN Liner CMP Process 193 6. CMP Process-Induced Defects 194 6.1. Defects in FEOL CMP 194 6.2. Defects in MOL Tungsten CMP 195 6.3. Defects in Cu BEOL CMP 195 6.3.1. Corrosion of Copper 196 6.3.2. Scratches 196 6.3.3. Dishing, Erosion, and Trenching 196 6.3.4. Mechanical Damage 197 6.3.5. Other Defects 197 7. Models of CMP Processes 198 7.1. Models Based on Contact Mechanics 198 7.2. CMP Process Models 199 8. Alternative CMP Processes 200 9. Concluding Remarks 201 10. Acknowledgments 201 11. References 201

Attraction between hydrophobic surfaces studied by atomic force microscopy

Abstract Attraction between hydrophobic surfaces, known as the hydrophobic force, is critically important for attachment of particles to air bubbles in flotation. However, the origins and models for this attractive force between hydrophobic surfaces have been a source of debate since the first direct measurements of this force in the early 1980s. Using an atomic force microscope (AFM) we studied the attraction between an AFM hydrophobic probe and a flat hydrophobic surface in water, in water–ethanol mixtures, and in water saturated by gases with different solubility. The strong attractive force with long-range jump-in attachment positions decreases with an increase in the ethanol content and disappears in pure ethanol. The size of steps on the force curves depends on the gas solubility. However, the measured forces do not depend on the gas solubility significantly. The influence of surface roughness and heterogeneity appear to be significant. Experimental results indicate the role of surface stabilized submicron-sized bubbles in the hydrophobic attraction. This is in line with recent direct and indirect evidences for the presence of gaseous bubbles at hydrophobic surfaces as well as with the early insights of flotation scientists.

Surface properties of barley straw

Surface properties of barley straw (Hordeum vulgare) play a crucial role in some industrial applications such as sorption in oil spills and soil clean-up. In this paper, the chemical and morphological heterogeneities of barley straw leaf and stem surfaces were investigated by water and oil contact angle measurements, Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and atomic force microscopy (AFM). The differences in the contact angles for internal versus external stem and leaf surfaces are explained by the presence of a complex wax layer at the external surface as revealed by FTIR external reflection spectroscopy. Wax composition was determined by transmission FTIR spectroscopy. SEM images confirmed the heterogeneity and complexity of the wax crystal structure of the outer stem surface. AFM measurements complemented the SEM analysis by providing additional structural details including a measure of surface roughness.

The dynamic nature of contact angles as measured by atomic force microscopy

Atomic force microscopy appears to be a useful tool for determining the contact angle for small particles. It is shown in this paper that the contact angle of a spherical polyethylene particle changes with the speed of the AFM piezoelectric translator. Such dynamic behavior of the contact angle and other uncertainties such as the position of the three-phase contact on the particle surface during bubble-particle interaction make it difficult to decide whether or not the AFM single-particle contact angle can be used to describe the hydrophobic state of the particle surface.

AFM measurements of hydrophobic forces between a polyethylene sphere and silanated silica plates-the significance of surface roughness

Recently, substantial research effort has been devoted to the study of non-DLVO forces between hydrophobic surfaces. However, the significance of surface roughness in the analysis of these hydrophobic attractive forces has not been given sufficient consideration and research is now in progress to attend to this issue. Fused silica plates covered with adsorbed octadecyltrichlorosilane (OTS) were characterized by water contact angle measurements and atomic force microscopy (AFM). Surfaces with different surface coverages and different contact angles were obtained by variation of the adsorption time. OTS formed patches on the silica surfaces, the lateral size and height of hich depended on the adsorption time. Such surfaces exhibit differences in roughness at the subnanometer level. Using the AFM colloidal probe technique, forces between a polyethylene sphere and silanated silica surfaces were measured in water. Long-range attractive forces were found, usually referred to as hydrophobic forces. The resulting force vs. distance curves were fitted with a double exponential function. The magnitude of the short-range part of the force curves seems to correlate with water contact angles at silanated silica surfaces. On the other hand, the range of the long-range force correlates with the roughness of the silanated silica surface. These results with silanated silica surfaces were compared with the AFM results for polyethylene and graphite surfaces and on the basis of these experimental efforts, it appears that the nature of these hydrophobic attractive forces is related to surface roughness.

Anisotropic Character of Talc Surfaces as Revealed by Streaming Potential Measurements, Atomic Force Microscopy, Molecular Dynamics Simulations and Contact Angle Measurements

Abstract A study of the interfacial properties of the basal plane and the edge surfaces of talc is described in this paper. The isoelectric points measured at two different crystallographic surfaces by the streaming potential method were found to be similar and exist at about pH 3.0. In the case of the edge surface, the zeta potential increases at higher pH values which can be attributed to the hydration of surface magnesium ions. The forces between the edge of a 20 μm talc particle and the two different crystallographic surfaces of talc were measured at various pH values using atomic force microscopy (AFM). These measurements show differences between the properties of the basal plane and edge of the talc. Finally, the differences in the hydration of the basal plane and the edge of talc are revealed from molecular dynamics (MD) simulations. The basal plane of talc is much less hydrated than the edge as can be seen from the water density distribution functions which correlate quite well with the contact angle measurements at the basal plane surface and the edge surface. Improved quality of the edge surface was achieved by sandblasting (erosion with alumina) and research regarding the characteristics of this edge surface is in progress.

A distribution of AFM pull-off forces for glass microspheres on a symmetrically structured rough surface

The adhesional contact between a particle and a substrate is a fundamental parameter for analyzing pull-off force data generated by atomic force microscopy (AFM). Roughness, present at some scale for all real materials, complicates this task by introducing asperity-controlled contact. Roughness also causes pull-off force data scatter, a well-known phenomenon that is usually neglected in analysis of the AFM pull-off results. This paper presents the first systematic study of roughness effect on the pull-off force magnitude and its distribution characteristics. The results indicate that the scatter in the data decreases with increasing diameter of the probe as compared to the dimension of surface irregularities, but the magnitude of the pull-off force is more severely altered by roughness. The results also show that when particle size is at the same scale as surface roughness, multiple contact points may be made yielding increased adhesion.

Preparation of hydrophobic microspheres from low-temperature melting polymeric materials

A novel procedure for the preparation of hydrophobic spherical particles from thermoplastic materials, such as polyethylene (PE) or fossil resin (FR), is presented. These particles are particularly useful in the determination of surface forces with the atomic force microscope using the colloidal probe technique. The preparation steps include (i) suspending powdered polymer (PE and FR) in glycerol, (ii) heating the suspension above the melting point of the polymer, (iii) solidification of dispersed PE/FR droplets at a reduced temperature, (iv) filtration of the particles, and (v) washing/drying of the product. Such produced particles of PE and FR had a broad size distribution (2-50 μm) and a spherical shape. The surfaces of these particles were relatively smooth, with a small number of asperities, and/or attached satellite particles or non-spherical debris. Analytical examination of the polymer surface, before and after treatment with hot glycerol, by SEM, AFM, contact angle, XPS, and FTIR measurements rev...

Air bubble and oil droplet interactions in centrifugal fields during air-sparged hydrocyclone flotation

The interactions of air bubbles and oil droplets in centrifugal flotation have been considered with respect to process conditions present during Air-sparged Hydrocyclone (ASH) flotation. Encounter efficiency of oil droplets with air bubbles has been found to be significantly smaller when compared to encounter efficiency of mineral particles. Collision and sliding contact times have been determined. Collision has been found to be insufficient for successful contact between oil droplets and air bubbles while sliding allows for film rupture depending on specific system conditions. Although the tenacity of oil droplet attachment to an air bubble is believed to be greater than the tenacity of a mineral particle, emulsification makes oil flotation in centrifugal devices with large dissipation of energy inefficient and hence requires the use of high molecular weight polymeric flocculants.

Interaction Forces Between a Coal Surface and a Polystyrene Sphere in the Presence of Cationic and Anionic Surfactants as Measured Using Atomic Force Microscopy

Abstract Interaction forces between hydrophobic coal particles and air bubbles during flotation are of significant academic and practical importance. When ionic surfactants are adsorbed by interacting surfaces, the flotation process can change due to changes in interfacial forces. An atomic force microscope (AFM) colloidal probe technique was used to measure the interaction forces between a coal surface and a polystyrene sphere in the presence of dodecylamine hydrochloride and sodium dodecylsulfate solutions. A significant dependence of these interaction forces on surfactant concentration was observed. In addition, zeta potential, bubble attachment time and contact angle measurements were performed, which together with AFM force measurements, give a more detailed description of this interfacial system involving two hydrophobic surfaces.