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Râmnicu Vâlcea, Romania

Ilie F.,Polytechnic University of Bucharest | Tita C.,School Group G ral Magheru
Optoelectronics and Advanced Materials, Rapid Communications | Year: 2010

In order understand the mechanisms of Chemical Mechanical Planarization (CMP), an Atomic Force Microscope (AFM) is used to characterize polished layer surfaces formed by selective transfer after a set of polishing experiments. The Atomic Force Microscopy (AFM) allows one to examine the effects of applying highly localized stress to a surface. In the presence of solutions tribochemical friction and wear can be investigated. We present results of a study on simultaneous application of chemical agents and mechanical stress involving a model single asperity and a solid surface. We show the consequences of combining highly localized mechanical stress (due to contact with AFM tip) and exposure to aqueous solutions of known pH. The experiment simulates many features of a single particle-substrate- slurry interaction in CMP. To optimize CMP polishing process, one needs to get information on the interaction between the abrasive slurry particles and the surface being polished. To study such interactions, we used all AFM. An AFM tip was used to mimic a single abrasive particle typical of those used in CMP slurry. Surface analysis of selective layer using the AFM revealed detailed surface characteristics of CMP. Studying selective layer in which predominanted copper (in proportion of over 85%) CMP, we found that the AFM scanning removes the surface oxide layer in different rates depending on the depth of removal and the pH of the solution. We show that linear scans and rastered scans display significantly different material removal rates. Oxide removal happens considerably faster than the CMP copper from selective layer removal. This is in agreement with generally accepted models of copper CMP. Quantitative models are presented to explain the observed nanometer-scale surface modifications. Both long-range and the friction forces acting between the AFM tip and surface during the polishing process were measured. The correlation between those forces and removal rate is discussed. In the same time this paper complements recent observations of tip-induced friction and wear and growth in a number of inorganic surfaces in aqueous solution. Source


Ilie F.,Polytechnic University of Bucharest | Tita C.,School Group G ral Magheru
Proceedings of the Institution of Mechanical Engineers, Part J: Journal of Engineering Tribology | Year: 2011

To understand the mechanisms of chemical mechanical planarization (CMP), an atomic force microscope (AFM) was used to characterize polished layer surfaces formed by selective transfer after a series of polishing experiments. The AFM allows one to examine the effects of applying highly localized stress to a surface. In the presence of solutions, tribochemical friction and wear can be investigated. We present the results of fundamental studies of the simultaneous application of chemical agents and mechanical stress using a single asperity model and a solid surface. At the same time, we show the consequences of combining highly localized mechanical stress (due to contact with AFM tip) and exposure to aqueous solutions of known pH. The experiment simulates several features of a single particle-substrate-slurry interaction in CMP. To optimize the CMP process, one needs to obtain information on the interaction between the slurry abrasive particles and the polished surface. To study such interactions, we used AFM. An AFM tip of radius of about 50 nm was used to mimic a single abrasive particle, typical of those found in CMP slurry. Surface analysis of selective layer using the AFM revealed detailed surface characteristics obtained by CMP. Studying the selective layer CMP, of which the predominant one is copper (in proportion of over 85 per cent), we found that the AFM scanning removes the surface oxide layer in different rates depending on the depth of removal and the pH of the solution. It was found that removal mechanisms depend also on the slurry chemistry, potential, percentage of oxidizer, and the applied load. We show that linear scans and raster scans display significantly different material removal rates. Oxide removal happens considerably faster than the copper CMP removal from the selective layer. This is in agreement with generally accepted models of copper CMP. Both long-range and the friction forces acting between the AFM tip and surface during the polishing process were measured. The correlation between those forces and removal rate is discussed. At the same time, this article complements recent observations of tip-induced friction and wear and growth in a number of inorganic surfaces in aqueous solutions. © Authors 2011. Source


Ilie F.,Polytechnic University of Bucharest | Tita C.,School Group G ral Magheru
Advanced Materials Research | Year: 2012

Molybdenum disulphides (MoS 2), which belong to the family of transition metal dichalcogenides, are well known for their solid lubricating behaviour. Thin films of MoS 2 exhibit extremely low coefficient of friction in dry environments, and are typically applied by mixed in oil, grease or impregnated into porous matrix of powdered materials, sputter deposition, pulsed laser ablation, evaporation or chemical vapour deposition and, which are essentially either line-of-sight or high temperature processes. Solid lubricant coatings are attractive because they can reduce friction-generated heat. MoS 2 is a common solid lubricant. However, the use of MoS 2 can limited by excessive wear, as well as a friction coefficient. Several studies on solid lubricant coatings demonstrated success in lubricating dry sliding contacts over very long periods in tribometer tests or reciprocating sliding experiments. Several pellet-on-disk and pad-on-disk tribometer tests were conducted to study the lubrication characteristics of third-body particles of MoS 2 powder. The tests consisted of simultaneous pellet-on-disk and pad-on-disk sliding contacts. Results from the tests show the self-repairing, self-replenishing, oil-free lubrication mechanism of MoS 2. A theoretical control volume fractional coverage (CVFC) model was developed to predict: - (1) the friction coefficient at the pad-on-disk interface and - (2) the wear coefficient for the lubricated pellet-on-disk sliding contact. The fractional coverage varies with time and quantifies the amount of third-body film covering the disk asperities. Results from the model capture the tribological behaviour of the experimental sliding contacts reasonably well. The aim of this paper is modeling and experimentation of solid lubrification with MoS 2 particles through self-repairing and self-replenishing and through the comparision between theoretical and experimental results obtained in the process of friction and wear by tribological tests. © (2012) Trans Tech Publications. Source


Ilie F.,University of Bucharest | Tita C.,School Group G ral Magheru
Journal of the Balkan Tribological Association | Year: 2012

Tungsten disulphides (WS 2), which belong to the family of transition metal dichalcogenides, are well known for their solid lubricating behaviour. Thin films of WS 2 exhibit extremely low coefficient of friction in dry environments, and are typically applied by mixed in oil, grease or impregnated into porous matrix of powdered materials, sputter deposition, pulsed laser ablation, evaporation or chemical vapour deposition and, which are essential either line-of-sight or high temperature processes. Solid lubricant coatings are attractive because they can reduce friction-generated heat. WS 2 is a common solid lubricant. However, the use of WS 2 can limit excessive wear, as well as the friction coefficient. Several studies on solid lubricant coatings demonstrated success in lubricating dry sliding contacts over very long periods in tribometer tests or reciprocating sliding experiments. Several pellet-on-disk and pad-on-disk tribometer tests were conducted to study the lubrication characteristics of third-body particles of WS 2 powder. The tests consisted of simultaneous pellet-on-disk and pad-on-disk sliding contacts. Results from the tests show the self-repairing, self-replenishing, oil-free lubrication mechanism of WS 2. A theoretical control volume fractional coverage (CVFC) model was developed to predict: (1) the friction coefficient at the pad-on-disk interface, and (2) the wear coefficient for the lubricated pellet-on-disk sliding contact. The fractional coverage varies with time and quantifies the amount of thirdbody film covering the disk asperities. Results from the model used for the tribological behaviour of the experimental sliding contacts are reasonably good. The aims of this paper are modelling and experimentation of solid lubrication with WS 2 particles through self-repairing and self-replenishing and through the comparison between theoretical and experimental results obtained in the process of friction and wear by tribological tests. Source

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