We evaluate the effect of chain length for a series of alkyl sulfonic acid additives on Cu electrodeposition by using a combination of electrochemical and Raman spectroscopic methods.

Polarization experiments in sulfuric acid based copper plating electrolytes disclosed unique mass‐transport limitations at very small cathodic overpotentials. Determination of the bulk concentration of the species, which is correlated to the observed limiting current plateaus, by means of Levich plots indicated that these plateaus may be related to mass‐transport‐limited copper deposition from cuprous ions. This hypothesis was further supported by comparison of the equilibrium constant of the comproportionation of cupric ions and metallic copper to cuprous ions obtained from experiments with literature values. The results provide a simple technique to detect cuprous ions and support the view that cuprous ions are deposited at a diffusion‐limited rate, whereas cupric ions deposition is controlled by electrochemical kinetics. The method may be of relevance for superfilling, since the action of additives in industrial plating electrolytes involves interaction with cuprous ions.

The temperature dependence of the comproportionation reaction of metallic copper and cupric ions to cuprous ions was studied by means of conventional polarization experiments. The bulk concentration of cuprous ions was determined by means of Levich plots based on mass‐transport limitations at very small cathodic overpotentials. The corresponding temperature dependence revealed increasing concentration with increasing temperature. This effect could be ascribed to enthalpy and entropy contributions to the Gibbs free energy of the equilibrium between the copper ion species, which were obtained by Van't Hoff analysis of the equilibrium constant. Formation of cuprous ions from metallic copper and cupric ions was found to be endothermic, but slightly favored by entropy. The results provide insights into the temperature dependence of industrial plating electrolytes, which is of increasing importance for upcoming advanced packaging applications like tall copper pillars. This approach should be especially suitable to determine the effects of industrially relevant additives in complicated, multi‐component electrolytes in the future.

The influence of the temperature-dependent Cu +1 -accelerator complex formation on through-silicon via (TSV) filling was studied by means of electrochemical polarization and plating experiments. Electrochemical studies revealed increasing cuprous ion concentration upon addition of the accelerator additive in comparison to the additive-free electrolyte and further increase upon increasing temperature. This indicated formation of a Cu +1 -accelerator complex. The electrochemical results were compared to TSV plating experiments at different temperatures. Despite improved mass transport of cupric ions into the high aspect ratio TSV feature at elevated temperatures, large voids were obtained under these conditions, while void-free bottom-up filling was achieved at room temperature. This effect was ascribed to acceleration of the copper deposition in the upper part of the feature due to increasing Cu +1 -accelerator complex concentration at higher temperatures. The resulting counter action the effect of the suppressor additive in this part of the features is assumed to yield the observed voids by closure of the features at an early stage of the plating process. Thus, the results presented here reveal the importance of taking into account the comprehensive impact factors on copper deposition for TSV applications and help to improve and fine tune the process to challenging structures.