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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.

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 -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 -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 -accelerator complexes, both of which exhibit different formation equilibrium constants.

Abstract Copper deposition in a plating bath known to fill narrow trenches was studied on a rotating disc electrode by impedance measurements. The chemistry of this bath contained, in addition to sulphuric acid, copper sulphate and chloride ions, polyethylene glycol (PEG) as an inhibitor and 3-mercapto-1-propanesulfonate, sodium salt (MPSA) as an accelerator. The experimental results were compared with a model taking into account these organic additives. A competitive adsorption of two complexes: PEG–Cl–CuI and CuISPS formed from Cu+ and the additives, is proposed. A good agreement was shown between this model and the experiments on fresh plating bathes.

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.

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.