The chemical mechanical planarization (CMP) of copper-based structures is typically carried out with slurries that contain an oxidant, a complexant, and a corrosion inhibitor. The dissolution and passivation of copper are strongly influenced by the pH and the redox potential of the slurry systems. In this paper, potential-pH diagrams for copper in aqueous systems containing various organic compounds and oxidants of interest to copper CMP are presented. The stability region of copper complexes under varying copper and ligand concentrations and the effect that they may have on copper removal during CMP are discussed. Experimental values of redox potentials in some of the chemical systems are included in the diagrams. In cases where the free energy of formation of organic ligands was not available in the literature, values were estimated using the group contribution method. © 2002 The Electrochemical Society. All rights reserved.

Sputter deposition has been investigated as a tool for manufacturing proton-exchange membrane fuel cell ͑PEMFC͒ electrodes with improved performance and catalyst utilization vs. ink-based electrodes. Sputter-depositing a single layer of Pt on the gas diffusion layer provided better performance ͑0.28 A/cm 2 at 0.6 V͒ than sputtering the Pt directly onto a Nafion membrane ͑0.065 A/cm 2 at 0.6 V͒ and equaled the performance of the baseline for an equivalent Pt loading. Sputter-depositing alternating layers of Pt and Nafion-carbon ink ͑NCI͒ onto the membrane did not increase the performance over the baseline as measured in amperes per centimeter squared due to the excessive thickness of the NCI ͑the NCI accounted for 99.9% of the electrode thickness͒. However, three and six layer Pt/NCI membrane electrode assemblies ͑MEAs͒ resulted in Pt activities double that of the 905 A/g at 0.6 V achieved by the ink-based baseline. Decreasing the thickness of each NCI layer increased the performance of the six-layered Pt/NCI MEA from 0.132 to 0.170 A/cm 2 at 0.6 V, providing an activity of 2650 A/g at 0.6 V. It is likely that by further decreasing the ratio of NCI to Pt in these electrodes, Pt activity, and PEMFC electrode performance can be increased.

Typically Pt is alloyed with metals such as Ru, Sn, or Mo to provide a more CO-tolerant, high-performance proton exchange membrane fuel cell (PEMFC) anode. In this work, a layer of carbon-supported Ru is placed between the Pt catalyst and the anode flow field to form a filter. When oxygen is added to the fuel stream, it was predicted that the slow H2 kinetics of Ru in this filter would become an advantage compared to Pt and Pt:Ru alloy anodes, allowing a greater percentage of O2 to oxidize adsorbed CO to CO2. With an anode feed of H2, 2% O2, and up to 100 ppm CO, the normalPt+normalRu filter anode performed better at 70°C than the Pt:Ru alloy. The oxygen in the anode feed stream was found to form a hydroxyl species within the filter. The reaction of these hydroxyl groups with adsorbed CO was the primary means of CO oxidation within the filter. Because of the resulting proton formation, the Ru filter must be placed in front of and adjacent to the Pt anode and must contain Nafion in order to provide the ionic pathways for proton conduction, and hence achieve the maximum benefit of the filter. © 2002 The Electrochemical Society. All rights reserved.

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Chemical mechanical planarization ͑CMP͒ has emerged as the most viable method to planarize copper thin films during fabrication of integrated circuits. The final stage of copper CMP requires the simultaneous polishing of copper and the barrier metal, where the metals are prone to galvanic corrosion due to exposure to slurry. In this study, the extent of galvanic corrosion between copper and tantalum was estimated using electrochemical polarization measurements. A novel setup was designed to make direct measurement of the galvanic current between copper and tantalum and was successfully used to measure galvanic current in two different chemical systems. Galvanic corrosion current values obtained from polarization and direct measurements are compared and their implications during barrier polishing are discussed.Chemical mechanical planarization or polishing ͑CMP͒ of copper is now routinely used for the formation of copper interconnect structures. In a CMP process, planarization of metal and dielectric areas is achieved by polishing a wafer with uneven topography on a polymeric pad held by a rotating platen using a colloidal slurry consisting of submicrometer-sized abrasive particles. Chemicals in the slurry, depending on their nature, play the role of oxidizer, slurry stabilizer, metal ion complexant, or corrosion inhibitor. In the abrasive-free polishing ͑AFP͒ process, the polishing medium consists of only chemicals and no particles.