Effects of Oximes on the Electrodeposition of Cobalt for Interconnect Applications
Authors: Lyons Tyler W. , Huang Qiang 
Published: February 2020

As the copper resistivity exponentially increases in the confined geometry of nanosized interconnects1, 2, the state-of-the-art semiconductor industry is in the process of replacing copper with new materials3. Cobalt has recently evolved as one of the top candidate materials due to its shorter electron mean free path4 as well as the manufacturability5, 6 and the potential benefits to the interconnect reliability7, 8. Super conformal electrodeposition of iron group metals has been recently studied for potential applications in interconnects and through silicon vias9-13. This paper presents a detailed comparison between the behaviors of a new class of additives, dioximes, during cobalt electrodeposition toward the defect-free formation of interconnects.

Cyclic voltammetry, chronopotentiometry with injection of additives, chronoamperometry with different agitation and additive concentrations as well as electrochemical impedance were carried out to characterize the behavior of additives. A quick strong suppression on Co deposition was observed upon the addition of the additives. While cobalt deposition was completely suppressed in presence of high rotation rate, the suppression effect disappeared in absence of agitation. A critical rotation rate was obtained, below which partial suppression was observed. A competition between the supply and adsorption of a suppressing intermediate species onto the electrode and the consumption of this intermediate by electrodeposition was hypothesized as the mechanism of partial suppression. Electrochemical impedance spectra suggested a strong inductance effect resulting from the perturbation of adsorption and desorption of the intermediate at rotation rates below the critical value. This was also consistent with the partial suppression effect and the hypothesized competition mechanism between the adsorption and consumption of an intermediate species. The comparison between different types of dioxime molecules elucidates the effects of molecular size, number of oxime groups, as well as the electron delocalization by aromatic groups on the suppression effects on cobalt electrodeposition.

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