Stephan Grunow

Using Sputter Deposition to Increase CO Tolerance in a Proton-Exchange Membrane Fuel Cell

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 mg/cm 2 and the amount of Ru in each Ru-containing anode was 0.080 mg/cm 2 . For an anode feed consisting of hydrogen, 200 ppm CO, and 2% O 2 (in the form of an air bleed), all Ru filter anodes outperformed the Pt:Ru alloy. The performance of the Pt + single-layer sputtered Ru filter was double that of the Pt:Ru alloy (0.205 vs. 0.103 A/cm 2 at 0.6 V). The performance was also significantly greater than that of the ink-based Ru filter (0.149 A/cm 2 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 OH ads formed from oxygen in the fuel stream to oxidize adsorbed CO to CO 2 .

Integration of PECVD Tungsten Nitride as a Barrier Layer for Copper Metallization

Amorphous tungsten nitride (WN x ) 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 WN 0.5 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 A WN 0.5 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 WN 0.5 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 WN 0.5 is demonstrated using stud-pull adhesion tests.

Comparison of Electromigration in Cu Interconnects with Atomic-Layer- or Physical-Vapor-Deposited TaN Liners

Electromigration in 0.07 μm wide Cu interconnections has been investigated for sample temperatures from 213 to 300°C. The effect of atomic-layer- or physical-vapor-deposited TaN x and physical-vapor-deposited Ta liner layers in Cu damascene lines on electromigration was also studied. A lower lifetime and activation energy for electromigration was observed in tested lines with sidewall voids. Similar electromigration lifetime and activation energy observed from samples with either atomic-layer- or physical-vapor-deposited TaN, suggested that the dominant diffusion paths in the Cu lines were not sensitive to the TaN x layer and were along the Cu/dielectric interface and/or grain boundaries.

Study of Electrochemical Deposition of Copper and Microstructure Evolution in Fine Lines

As computer chip technologies evolve from aluminum-based metallization schemes to their copper-based counterparts, Electrochemical Deposition (ECD) is emerging as a viable deposition technique for copper (Cu) interconnects. This paper presents the results of a first-pass study to examine the underlying mechanisms that control ECD Cu nucleation, growth kinetics, and post-deposition microstructure evolution (self-annealing), leading to the development and optimization of an ECD Cu process recipe for sub-quarter-micron device generations. The influence of bath composition, current waveform, type and texture of Cu seed layer, and device feature size (scaling effect) on the evolution of film texture, morphology, electrical properties, and fill characteristics was investigated using a manufacturing-worthy ReynoldsTech 8” wafer plating tool. Resulting films were analyzed by X-ray Diffraction (XRD), four-point resistivity probe, Focused-Ion-Beam Scanning Electron Microscopy (FIB-SEM), and Atomic Force Microscopy (AFM). These investigations identified an optimized process window for the complete fill of aggressive device structures with pure Cu with resistivity ∼ 2.0 µΩ-cm and smooth surface morphology.