• Energy Research

Abstract We apply a 2 5−1 fractional factorial Design of Experiments (DoE) test plan in order to discriminate the direct effects and interactions of five factors on the water management of a 500 We PEMFC stack. The stack is submitted to current steps between different operating levels and several responses are extracted for the DoE analysis. A strong ageing effect on stack and cell performances is observed. Therefore, in order to perform the DoE analysis, responses which values are too strongly affected by ageing are “corrected” prior to the analysis. A “virtual” stack, considered as “healthy”, is also “reconstructed” by “putting in series” the cells exhibiting very low performance drop. The results show that stacks and cells' resistivities are mostly impacted by direct effects of both temperature and cathodic inlet relative humidity and by compensating interaction between temperature and anodic overstoichiometric ratio. It also appears that two responses are able to distinguish a “healthy” stack from a degraded stack: heterogeneities in cell voltages and cell resistivities distributions. They are differently impacted by considered effects and interactions. Thus, a customised water management strategy could be developed, depending on the stack's state of health to maintain it in the best possible operating conditions.

Electrochemical impedance spectroscopy and cyclic voltammetry were used to characterize the aging of copper plating baths used in damascene process for superfilling of trenches and vias in the semiconductor industry. The effects of copper anode composition, anodic current density, and accelerator nature and concentration were studied. Phosphorus added to copper anodes has a prominent impact on the evolution of current/voltage curves and impedance spectra during bath aging. The observed evolutions were explained by the formation of a Cu I -accelerator complex in the bulk of the bath that adsorbs at the copper surface to act as an accelerating species, and by the increase of its concentration during aging with undoped copper anode. The Cu I -accelerator complex formation is limited by the phosphorus contained in the Cu-P anode, which traps electrogenerated cuprous ions in the black anodic film. Differences observed between baths containing SPS (bis(3-sulfopropyl)disulfide) or MPSA[(3-mercaptopropane)sulfonic acid] are also attributed to the existence of two different Cu I -accelerator complexes, both of which exhibit different formation equilibrium constants.

The influence of both soluble and insoluble anodes on the kinetics and morphology of the copper deposit in the damascene process was investigated by voltammetry and impedance techniques. A plating bath known to provide conformal superfilling of trenches and vias in the microelectronic industry was used. It was shown that the use of a glassy carbon anode leads to faster degradation of the plating bath which is detrimental to the copper deposit. A copper anode decreases the aging rate by limiting the anodic potential compared to the glassy carbon anode where high anodic potentials prevail during the copper deposition process.

Abstract Water management is critical for PEMFCs, especially at system level. To study its impact on the performance and obtain useful indicators for fault detection, two commercial stacks were characterized by impedance spectroscopy under various humidities and current densities. One was fresh while the other was operated on-field during 10 000 h. Four capacitive and one inductive loops are identified. The capacitive loops are attributed to charge transfer kinetics at both anode and cathode and to cathodic and anodic mass transfer limitations. The inductive loop is attributed to oscillations in the ionomer water content induced by oscillations in the amount of produced water during the measurement. The size of the cathodic charge transfer loop and its departure angle at high frequencies increase as humidity decreases because the ionomer conductivity decreases. These parameters are potential indicators of the cathode drying. The angles are below 45° at low humidities but close to 90° in sur-saturated conditions.

Electrochemical impedance spectroscopy was performed on copper interconnect plating baths during deposition to study their degradation (ageing). A kinetic-based model was used to simulate the impedance scans by taking into account the organic additives in the reaction mechanism. Also, an equivalent circuit analysis was performed to characterize the deposition process in terms of resistive and capacitive components. Experimental results for two chemistries indicate that the low-frequency impedance relaxations change as the plating bath ages. Impedance diagrams calculated from the kinetic model resulted in a reasonable fit with the experimental impedance scans. In addition, the low-frequency capacitive and inductive impedance loop diameters are proposed as parameters to follow bath ageing. From these results, a monitoring method is proposed which could be applied to an industrial production line.

Abstract The mechanism of copper deposition in a sulphuric acid–sulfate bath in the presence of chlorides was investigated by electrochemical impedance measurements. A model where the chloride ions added to a sulphuric acid–sulfate copper-plating bath have a catalytic action not limited by mass transport has been proposed. This shows that the observed mass transport limitation is due to the diffusion of cupric ions and that, at high current densities, the copper deposition is mainly due to a mechanism involving CuCl formation on the electrode.

Electroacoustic admittance measurements were performed on copper bath solutions containing additives that are used in the copper damascene process. Preliminary results have shown that an electroacoustic admittance parameter can be defined that varies with additive concentration. It is proposed that quartz resonators may be suitable sensors for monitoring copper bath additives.

Electrochemical impedance measurements were performed on copper bath solutions during copper deposition and subsequent aging of the bath. The results show a correlation between the low-frequency capacitive loop of the electrochemical impedance and copper deposit roughness. The deposit became smoother as the bath aged and reached an optimal value, after which the deposit became rougher. The optimal surface smoothness correlated with a minimum in the low-frequency capacitive loop diameter of the impedance. The results suggest that electrochemical impedance measurements may be used to monitor changes in the copper bath that affect copper deposit quality and superfilling capability.