Corresponding Author

Mao-Zhong An(mzan@hit.edu.cn)


As the semiconductor integrated circuits evolve into 7 nm technology and beyond, the resistance of the Cu filling at back-end-of-line interconnects no longer linearly scales with dimension. The metal Co with lower mean free path can be used to replace Cu for reducing the line resistance caused by the scattering on the outer surface and grain boundary in the smaller and smaller size. In this study, CoSO4 was used as the main salt, boric acid as a buffer and malachite green (MG) as an inhibitor for further research. According to the electrochemical cyclic voltammetric (CV) curves by using a rotating disk electrode, the reductive overpotential of the metal Co shifted negatively and the reduction process was gradually suppressed with the increasing concentration of the additive MG. Besides, the deposition current density decreased and the current efficiency of the reduction process declined after adding MG from the electrochemical quartz crystal microbalances (EQCM) test. This is because of the MG adsorption on the surface and complexation with the metal Co ion in the bath. Hence, MG has a significant inhibition effect in the deposition process, which reduces the deposition efficiency. At -1.27 V, the current density of the total reduction process gradually decreased with the applying higher rotation rate and returned to the initial value within a few minutes after suspending. The current density was heavily influenced by the convection process. At last, the bottom-up superfilling of blind via from an aqueous solution containing 0.4 mol·L-1 CoSO4, 0.5 mol·L-1 H3BO3, a small amount of Cl-, 20 mg·L-1 MPS and 10 mg·L-1 MG at -1.27 V with the pH 4. From the chronoamperometric curves, the appearance of two peaks was mainly attributed to the hydrogen evolution process and the nucleation process of Co2+ reduction, and the nucleation process was three-dimensional instantaneous nucleation process. In order to further studying the construction of the MG, and the bonding between additive MG and cobalt ions, the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) of MG are obtained by quantum chemical calculation, indicating the active site distributed on the conjugate structure of aniline and amido cyclohexadiene for adsorbing on the cathode surface. The electrostatic potential (ESP) diagram is obtained by molecular dynamics simulation, and the results point out that the potential distributes at 35 ~ 78 kcal·mol-1, meaning the easily adsorption of additive MG on the cathode surface. The complex of CoMG was formed from delocalized pi-bond of phenyl of MG and free Co ion in the bath.

Graphical Abstract


inhibitor, cobalt; superfilling, nucleation process, electrostatic potentials

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