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Placing a layer of Ru atop a Pt anode increases the carbon monoxide tolerance of proton-exchange membrane fuel cells when oxygen is added to the fuel stream. Sputter-deposited Ru filter anodes composed of a single Ru layer and three Ru layers separated by Nafion-carbon ink, respectively, were compared to Pt, Pt:Ru alloy, and an ink-based Ru filter anodes. The amount of Pt in each anode was 0.15 normalmg/cm2 and the amount of Ru in each Ru-containing anode was 0.080 normalmg/cm2. For an anode feed consisting of hydrogen, 200 ppm CO, and 2% O2 (in the form of an air bleed), all Ru filter anodes outperformed the Pt:Ru alloy. The performance of the normalPt+normalsingle­normallayer sputtered Ru filter was double that of the Pt:Ru alloy (0.205 vs. 0.103A/cm2 at 0.6 V). The performance was also significantly greater than that of the ink-based Ru filter false(0.149A/cm2 at 0.6 V). Within the filter region of the anode, it is likely that the decreased hydrogen kinetics of the Ru (compared to Pt) allow for more of the OHnormalads formed from oxygen in the fuel stream to oxidize adsorbed CO to CO2. © 2002 The Electrochemical Society. All rights reserved.

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Electrochemical studies are designed to identify processes that provide adequate nucleation and thin film growth directly on ultrathin, air-exposed physical vapor deposition (PVD)-tungsten nitride diffusion barriers. In this study, it is shown that very thin copper films can be nucleated directly on a conducting PVD-W 2 N liner surface. A complex chemistry model based on mass balance and thermodynamic equilibrium has been applied to numerous ammoniacal platting bath compositions and the resulting concentration profiles inserted into the Nernst equation. Comparing the experimental results with the predicted model indicates that a strong adhesion is associated with the reduction of several copper-ammonia complexes at the metal nitride surface. Nucleation, growth mechanisms, and film resistivity are found to be dependent on the reduction potential, electrolyte velocity, and platting bath chemistry.

Amorphous tungsten nitride (WNx) is a promising diffusion barrier for extending Cu metallization beyond 0.18 μm. This study evaluates the barrier performance, adhesion, and step coverage of PECVD WN 0.5 integrated with a CVD Cu seed layer. The WN0.5 films exhibit amorphous structure with 33% bottom and side-wall step coverage in 0.14 μm wide structures with 9:1 aspect ratio. The potential of 50 Å WN0.5 as an effective Cu barrier is shown by the absence of Secco etch-pits in the Si substrate after a 30 min anneal at 500°C. When deposited on PECVD WN0.5 the CVD Cu films exhibit uniform nucleation, and as deposited resistivity of 2.5 μΩ-cm. Step coverage of the CVD Cu is better than 95% in 0.14 μm structures. Adhesion exceeding epoxy strength of the CVD Cu seed layer even to air-exposed WN0.5 is demonstrated using stud-pull adhesion tests.