(Digital Presentation) Operando Laser Scattering- and Inverted RDE-Based Approaches for the Development of Additive-Assisted Electrodeposited Co Interconnects
Authors: Moreno Garcia Pavel , Grozovski Vitali , Gálvez-Vázquez María de Jesús , Fluegel Alexander , Kitayaporn Sathana , Vesztergom Soma , Broekmann Peter 
Published: July 2022

The development of Co interconnects by electrochemical means is more challenging than that of Cu-based analogues not only due to the ever decreasing critical feature dimensions but also to intrinsic complications of the water/Co system, as Co electrodeposition processes are inevitably accompanied by the competing hydrogen evolution reaction (HER). Aiming at enabling a more knowledge-driven Co interconnect development, we present herein two novel experimental approaches that reveal important insights on the complex interplay between additive-assisted Co electrodeposition and the HER.

In a first instance, we present a custom-made inverted RDE instrument, particularly suitable for studying metal deposition processes that are accompanied by HER or any other gas evolving side reaction. We investigate the influence of a model redox-active suppressor additive on the electrochemical deposition of cobalt by means of linear sweep voltammetry and galvanostatic electrolysis coupled to online gas chromatography analysis. We find that under specific experimental conditions, addition of minor amounts of the additive to the standard Co-based virgin make-up solution significantly decreases the rate and efficiency of Co deposition, and favors instead the competing HER. Moreover, we identify and quantify the reductive conversion of the additive that accompanies the primary metal deposition process. Importantly, our approach complements standard screening Co plating studies as it succeeds to directly deconvolve the overall process into its three individual components, namely the metal ion reduction, the HER and the additive activation.

Secondly, to develop understanding of proton dynamics in the diffusion layers generated by the metal electrodeposition processes we introduce a simple, non-invasive pH-sensing approach that is based on the Tyndall effect enhancement modulated by pH-controlled agglomeration events. We employ a laser beam laterally aligned to an electrode surface where additive-assisted cobalt deposition and hydrogen evolution take place simultaneously. This configuration allows the visualization of pH changes that result in precipitate formation and that extend to greater distances over patterned surfaces compared to flat ones, demonstrating a pH-guiding effect in superconformal metal deposition. The method provides real-time visualization of the pH dynamics with high lateral spatial resolution without physically or chemically influencing the investigated system. We suggest that applicability of the method can be extended to other processes where nanoaggregation/decomplexation inherently occur, as part of the investigated phenomena, at light-addressable interfaces.

Overall, these investigations provide new insights for the further development of interconnect technology and metal deposition processes in general.

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