Vimal Desai

Mechanism of Copper Removal during CMP in Acidic H 2 O 2 Slurry

Chemical mechanical polishing of copper was performed using as oxidizer and alumina particles as abrasives. Electrochemical techniques were used to investigate the dissolution/passivation behavior of high-purity Cu disk under static and dynamic conditions at pH 4 with varying concentrations. Changes in the surface chemistry of the statically etched Cu disk were investigated using X-ray photoelectron spectroscopy. The Cu removal rate reached a maximum at 1% concentration and decreased with a further increase in concentration. The static etch rate showed the same trend. The etched surface morphology indicates that the removal of copper is primarily the result of electrochemical dissolution of copper at low concentrations. However, at increased concentrations, the copper oxidation rate increases, resulting in a change in the Cu removal mechanism to mechanical abrasion of the oxidized surface.

Electrochemical characterization of copper chemical mechanical polishing

Chemical mechanical polishing (CMP) of copper was performed using H2O2 as oxidizer and alumina particles as abrasives. The interaction between the Cu surface and the slurry was investigated by potentiodynamic measurements taken during the polishing process as well as under static conditions. The Cu removal rate reached a maximum at 1% H2O2 concentration, and decreased with a further increase in H2O2 concentration. The static etch rate showed the same trend. Atomic force microscopic measurements were performed on both the etched surface and polished surface. It was shown that the surface roughness of the polished surface increased as the H2O2 concentration increased. This can be explained by changes in the structure of the passivating layer and the dominating role of the dynamic repassivation during polishing.

Polishing mechanism of tantalum films by SiO 2 particles

Dishing and erosion are major problems in conventional chemical mechanical planarization of copper/barrier layers. Understanding the polishing mechanism of the different materials involved can assist in providing a solution to these issues. Chemical mechanical polishing of tantalum was performed using alumina and silica particles dispersed in deionized water at pH 6. Tantalum shows a higher removal rate in silica slurry compared to alumina slurry. To examine the polishing mechanism of tantalum in silica slurry, the surface structure of the film was investigated by X-ray photoelectron spectroscopy (XPS). Various electrochemical techniques were used to characterize the surface film formation, dissolution and the interaction between silica particles and tantalum film. XPS and electrochemical results indicate that tantalum film may react with silica particles to form Ta-O-Si bonds on the surface. The mechanical tearing of Ta-O-Si bonds leads to the removal of Ta2O5 as a lump, resulting in higher removal rates of tantalum in silica slurry.

Effect of multiphase flow on corrosion of C-steel in presence of inhibitor : a surface morphological and chemical study

Abstract This communication reports the effects of multiphase flow on the corrosion product formed on the surface of 1018 C-steel coupons in oil and gas lines in presence of inhibitor oleic imidazoline. Both bulk and surface analytical techniques reveal the presence of FeCO 3 , a classic example of CO 2 corrosion. While significant changes in the surface morphology with flow condition are monitored by SEM and OM, detailed AES and XPS analysis show the deterioration of inhibitor chemistry as the flow is increased from full pipe (Fr = 0) to slug flow (Fr = 6). XPS shakeup satellite lines in the N (1s) spectra have been useful in the analysis.

Surface chemistry of Nextel-720, alumina and Nextel-720/alumina ceramic matrix composite (CMC) using XPS–A tool for nano-spectroscopy

Abstract Oxide-based ceramic matrix composites (CMCs) are prime candidates for high temperature turbine applications. Increasing demand of CMCs necessitates the development of quality monitoring procedures. Sol–gel derived Nextel-720 fiber/alumina matrix CMC is one of the potential candidate material for land-based gas turbine applications. X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) were utilized to investigate any surface/interface chemical alteration of the Nextel-720 fiber reinforcement and the alumina matrix during fabrication. The calculated XPS spectra of the composite were obtained by simply adding the spectra of the as-received Nextel-720 fiber and the alumina matrix. The calculated XPS spectra and the acquired XPS Al(2p), Si(2p3), and O(1s) spectra from the as-received materials were compared using a superimposition method to investigate any chemical alteration during composite fabrication for quality control measures. This paper is aimed to serve as a reference for future XPS studies of CMCs exposed to aggressive turbine environments.

Studies on passivation behavior of tungsten in application to chemical mechanical polishing

Chemical mechanical polishing (CMP) is considered to be the enabling technology for meeting the planarization requirements in <0.35 μm feature sized multilevel semiconductor device fabrication. CMP of tungsten is done in order to planarize and remove excess tungsten in the process to form inter-level contacts. Considerable importance is given to the role played by the passive oxide film formation on the surface during tungsten CMP. In this study, x-ray photoelectron spectroscopy (XPS) is used to understand the oxide growth mechanism in tungsten. Tungsten wafers are polarized to different anodic potentials in static pH 4 solutions of KIO3 and H2O2, two commonly used oxidizers in CMP. XPS measurements are employed to probe the chemical and stoichiometric changes in the surface oxide films treated under these conditions. These results are then compared with the electrochemical polarization results.

Role of oxidizer in the chemical mechanical planarization of the Ti/TiN barrier layer

The electrochemical parameters controlling the polishing rates of Ti and TiN are investigated. In this paper, alumina containing slurry was studied at pH 4 with 5% H2O2 as the oxidizer. Passive film formation on the surface during chemical mechanical polishing (CMP) plays an important role. To understand the oxide growth mechanism and the surface chemistry, X-ray photoelectron spectroscopy was performed. It was found that in the absence of an oxidizer, the removal of Ti and TiN is mainly due to mechanical abrasion of oxide layer or metal layer. However, in the presence of 5% H2O2 as the oxidizer, different removal behavior was observed for Ti and TiN. The removal mechanism of Ti during CMP is mainly due to mechanical abrasion of the oxide layer whereas for TiN it could be attributed to the formation of metastable soluble peroxide complexes.

High-temperature oxidation resistance improvement of titanium using laser surface alloying

Commercially pure titanium substrate was coated with aluminium by flame spraying or arc spraying techniques and was irradiated with a laser to form a laser-alloyed zone (LAZ). The microstructure of the LAZ was investigated. High-temperature oxidation tests were carried out in air at different high temperatures and the characteristics of the oxide layer were investigated using Auger electron spectroscopy. The aqueous corrosion tests were carried out in 3.5% NaCl solution at room temperature. The laser-processed material showed considerable improvement in the high-temperature oxidation-resistant property while the aqueous corrosion-resistant property of the LAZ was found to remain almost unaffected.

Role of surface chemistry on the nature of passive oxide film growth on Fe–Cr (low and high) steels at high temperatures

High temperature materials degradation or protection of Fe–Cr alloys are often related to the nature of their oxide scale formation. Breakdown of passive oxide films leads to localized corrosion. Various alloying elements are often incorporated in these alloys to prevent high temperature oxidation. The addition of selected alloying elements is cumbersome and not always cost effective. In this article, we investigate the role of rare earth oxide coatings on high temperature corrosion prevention of both low and high Cr steel. An in situ high temperature oxidation setup has been built to study the oxidation kinetics of both coated and uncoated low and high Cr steels under ambient pressure and dry air. Reduction in scale growth kinetics is observed in the presence of coating. While scanning electron microscopy and x-ray diffraction are employed to study the structure and morphology of the oxide films, x-ray photoelectron spectroscopy and Auger electron spectroscopy are used to study the surface chemistry of t...

Effect of Film Cooling on Low Temperature Hot Corrosion in a Coal Fired Gas Turbine

In recent times, the use of coal gas in gas turbines has gained a lot of interest, as coal is quite abundant as a primary source of energy. However, use of coal gas produces a few detrimental effects that need closer attention. This paper concentrates on one such effect, namely hot corrosion, where trace amounts of sulfur can cause corrosion (or sulfidation) of hot and exposed surfaces, thereby reducing the life of the material. In low temperature hot corrosion, which is the focus of this paper, transport of SO2 from the hot gas stream is the primary process that leads to a chain of events, ultimately causing hot corrosion. The corrosion rate depends on SO2 mass flux to the wall as well as wall surface temperature, both of which are affected in the presence of any film cooling. An analytical model is developed to describe the associated transport phenomena of both heat and mass in the presence of film cooling The model predicts how corrosion rates may be affected under operating conditions. It is found that although use of film cooling typically leads to lower corrosion rate, there are combinations of operating parameters under which corrosion rate can actually increase in the presence of film cooling.Copyright