Simulating the Influence of Supporting Electrolyte Concentration on Copper Electrodeposition in Microvias

Robust, void-free Cu electrodeposition in high-aspect ratio features relies on careful tuning of electrolyte additives, concentrations, and electrochemical parameters for a given feature dimension or wafer pattern. Typically, Cu electrodeposition in electronics manufacturing of microscale or larger features (i.e., microvias, through-holes, and high-density interconnects) employs a CuSO4 – H2SO4 electrolyte containing millimolar levels of chloride and, at a minimum, micromolar levels of a polyether suppressor. Research and optimization efforts have largely focused on the relationship between electrolyte additives and growth morphology, with less attention given to the impact of supporting electrolyte. Accordingly, a computational study exploring the influence of supporting electrolyte on Cu electrodeposition in microvias is presented herein. The model builds upon prior experimental and computational research on localized Cu deposition by incorporating the full charge conservation equation with electroneutrality to describe potential variation in the presence of ionic gradients. In accord with experimental observations, simulations predict enhanced current localization to the microvia bottom as H2SO4 concentration is decreased. This phenomenon derives from enhanced electromigration within recessed features that accompanies the decrease of conductivity with local metal ion depletion. This beneficial aspect of low acid electrolytes is also impacted by feature density, CuSO4 concentration, and the extent of convection.

Measuring Parasitic Heat Flow in LiFePO4/Graphite Cells Using Isothermal Microcalorimetry

Isothermal microcalorimetry has previously been used to probe parasitic reactions in Li-ion batteries, primarily studying Li[NixMnyCo1-x-y]O2 (NMC) positive electrode materials. Here, isothermal microcalorimetry techniques are adopted to study parasitic reactions in LiFePO4 (LFP)/graphite cells. Features in the heat flow from graphite staging transitions were identified, and the associated heat flow was calculated using simple lattice-gas mean-field theory arguments, finding good agreement with experimentally measured values. Parasitic heat flow was measured in LFP/graphite pouch cells with different electrolyte additives. In an electrolyte without additives, a massive parasitic heat flow was measured suggesting a shuttle reaction unique to the LFP/graphite system. In cells containing electrolyte additives, parasitic heat flow agreed well with long-term cycling results, confirming the value of this technique to rank the lifetime of LFP/graphite cells with different electrolyte additives. Finally, comparing cells with and without unwanted water contamination, it was found that the parasitic heat flow was similar or slightly higher in cells where water was intentionally removed before cycling, seemingly contradicting long-term cycling results. It is concluded that the presence of water (at the 500 ppm level) may slightly reduce parasitic reactions, but at the expense of a more resistive SEI layer.