Simulating Cu Electrodeposition in High Aspect Ratio Features: Effect of Control Mode and Uncompensated Resistance in S-NDR Systems
Trevor Braun, Daniel Josell, Thomas P. Moffat
Void-free Cu electrodeposition in high aspect ratio features relies on preferential growth proceeding from the most recessed surfaces where sustained breakdown of the co-adsorbed polyether-halide suppressor layer occurs. Localization is the result of positive feedback between inhibitor breakdown and metal deposition subject to transport limitations on the suppressor precursor(s). This gives rise to a negative differential resistance (S-NDR) that, convolved with uncompensated ohmic resistance, results in electrode bifurcation into active and passive zones. The interplay between the additive derived S-NDR behavior, uncompensated cell resistance, and potentiostatic regulation is explored in comparison to galvanostatic feature filling. Uncompensated resistance arises from the working electrode contact and electrolyte between the working and reference electrode. For a CuSO4 – H2SO4 electrolyte containing 80 μmol/L Cl- and 40 μmol/L polyether, simulations of potentiostatic deposition with minimal uncompensated resistance reveal a narrow window between fully passive and voided feature filling; bottom-up filling even terminates prematurely under the most favorable conditions. In contrast, optimized galvanostatic operation enables void-free feature filling with termination dictated by the operator. Increasing the uncompensated resistance along with application of accordingly more negative applied potentials produces filling dynamics that blends the positive attributes of galvanostatic and potentiostatic deposition to enable complete, void-free feature filling with spontaneous passivation near the feature opening. Importantly, these beneficial filling effects are also evident for via and trench arrays with variable widths or heights.
, Josell, D.
and Moffat, T.
Simulating Cu Electrodeposition in High Aspect Ratio Features: Effect of Control Mode and Uncompensated Resistance in S-NDR Systems, Electrochimica Acta
(Accessed June 4, 2023)