Influence of the Temperature-Dependent Cu⁺¹-Accelerator Complex Formation on Through-Silicon Via Filling

Abstract

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.

Interfacial Leveler-Accelerator Interactions in Cu Electrodeposition

“…16 Previous work shows that SPS undergoes decomposition at the Cu surface, starting from either the original dimer state of SPS or as 3-mercapto-1propanesulfonate (MPS) (the monomer equivalent of SPS), to form a surface-adsorbed Cu-thiolate species. 17,18 Acceleration in the presence of SPS has been ascribed to both enhanced formation of soluble Cu + intermediates by complexation of Cu + with thiolate species 10,19,20 and stabilization of desolvated Cu 2+ species by the surface proximal sulfonate moiety of SPS. 20 In contrast, the suppressor, most commonly polyethylene glycol (PEG), 16,21 polypropylene glycol (PPG), 21 or PEG-PPG copolymers, decreases the rate of Cu reduction.…”