When pure aluminum is passivated at constant applied voltage in solutions ranging from pH 0–7, the current density representing film growth falls during the first few seconds in a manner that is qualitatively and nearly quantitatively the same for all solutions. The fall of current is succeeded by a rise to a constant value; the rise occurs the earlier, and is the greater, the lower the pH. The fall is interpreted as caused by barrier‐layer formation, and the rise as caused by pore initiation when the field across the barrier layer has fallen low enough to allow the entry of protons into the film. Electron micrographs of the film surface show that very few pores are present on specimens that have not been anodized long enough for the initial current fall to halt, and that the pore system is fully established as soon as the succeeding rise is complete. A mechanism for pore formation is proposed.

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Anodizing of magnesium was studied in solutions containing 3MKOH+0.6MKF+0.21MNa3PO4 , with and without addition of 0.4 M and 1.1 M of aluminate. At constant applied current, the process occurs in two stages. First, the voltage rises linearly until an initial breakdown occurs. A thin and compact oxide film is formed at this stage. In the second stage an intense continuous spark is maintained on the metal surface. A thick oxide film is formed at the site of sparking. The formation of the film is accompanied by voltage oscillation and gas evolution. The anodic films formed under continuous breakdown conditions are rough and porous and enriched in aluminum. Anodic films formed in a bath containing 1.1 M aluminate at 15 normalmA/cm2 are composed of a single oxide phase MgAl2O4 spinel. © 1999 The Electrochemical Society. All rights reserved.

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Electropolishing of thin films poses additional challenges in comparison to bulk material polishing. The existence of a resistive anode/electrolyte boundary layer is crucial for achieving polishing. A finite amount of copper is required to be anodically dissolved to create the boundary layer of the appropriate thickness for effective electropolishing of a given hillock. This is a significant consideration in the application of electropolishing for planarization of thin films where the disparity in the topography is significant in proportion to the thickness of the film. Here electropolishing is shown to effectively remove the bulk of electrodeposited copper layers used in ultralarge scale integration (ULSI) metallization schemes without application of mechanical force and to planarize local topography. Efficient polishing can be achieved under galvanostatic conditions (i.e., constant current between the wafer and a counter electrode). Anodic transient studies indicated that the mechanism of formation of the boundary layer (in mass-transport controlled regime) is determined by the diffusive transport of an acceptor species to the anode/electrolyte interface. Effects of changes in current density and rotational speed of wafer on the extent of planarization have been determined. Under optimal galvanostatic and hydrodynamic conditions, the disparity in the topography over wide trenches adjacent to dense features decreased by 60%. © 2002 The Electrochemical Society. All rights reserved.

The structure of cobalt formed by electrodeposition and the influence of the pH of the plating solution and the cathode potential was studied by potentiodynamic measurements and X-ray diffraction. It was found that the level of overpotential significantly affects the structure of the formed cobalt. When electrodeposition is performed far from equilibrium conditions, i.e., at a high overpotential, face-centered cubic ͑fcc͒ cobalt is deposited while at low overpotential hexagonal close packed Co is formed with a lower rate of hydrogen evolution. A higher overpotential is needed in a neutral compared to acidic solution in order to enhance the evolution of hydrogen that is required for the formation of fcc cobalt.There is a growing interest in magnetic thin films, especially in cobalt films, due to their wide range of application as magnetic data storage devices. 1-5 These films are usually prepared by physical deposition methods which require ultrahigh vacuum techniques. [6][7] An alternative processing technique is electrodeposition. Electrodeposition has several advantages over dry processes. 8 Electrodeposition does not require vacuum technology and consequently is less expensive. It can easily be upscaled for use in large size areas, and it is capable of depositing uniform films on complex surfaces without the shadowing effects often encountered in other deposition methods. The experimental systems used are much simpler than evaporation or sputtering apparatus, and electrodeposition can be a room-temperature technology. However, there are some drawbacks associated with the process, such as the need for a conducting/ semiconducting substrate, the limited number of elements that can be deposited, and the large number of variables that influence this process ͑composition, pH, concentration, current density, temperature, agitation, etc.͒.Hexagonal close packing ͑hcp͒ is the usual structure for electroplated cobalt. It is also known, 9 that face-centered cubic ͑fcc͒ cobalt, which is stable at temperatures above 422°C, can sometimes be obtained from electrodeposition at ambient temperatures. Gelchinski et al. 10 have electroplated, at room temperature, cobalt-chromium alloys containing the cP8 structure type, 11,12 that is stable only at high temperatures, according to the equilibrium phase diagram.Several researchers 9,13-22 have reported that the pH of the bath solution significantly affects the structure of cobalt formed by electrodeposition. A solution with a low pH (Ͻ2.5) was reported to favor fcc cobalt, 9,13-22 whereas a high pH (Ͼ2.5) or a high temperature system favored the formation of hcp cobalt in a sulfate bath with no organic additives. 14 Agitation of a sulfate bath also favored hcp cobalt. A high deposition temperature in a chloride bath also induced the formation of hcp cobalt, 17,18 whereas high current densities in sulfamate solutions were found to favor the cubic structure. 19 In addition, a high degree of preferred orientation has been observed by Sard et al. 18 for cobalt formed in sulfate baths....