Electrochemical Nucleation and Growth of Cobalt in Presence of Dioxime Additives
Authors: Hu Yang , Huang Qiang 
Published: February 2020

The concerns about copper (Cu) interconnects have been increasing because the Cu line resistance will not linearly scale with the dimension in 7 nm technology and beyond1. Instead, Cu resistivity in small features increases significantly because of the electron scattering at grain boundaries and interfaces2. To solve this problem, alternative metals such as cobalt (Co) is considered as a promising material because of its high melting point and small mean free path. High melting temperature lows the risk of electromigration3 and small mean free path decreases the contribution from electron scattering at boundaries and interfaces.
Recently, defect-free filling of Co in nanoscale features has been achieved using proprietary additives4-6. The additives play an important role in such processes creating differential plating rates between the feature bottom and field regions. Different functional groups in organic additives were found to influence electrodeposition kinetics. For instance, additives with a conjugated pair of oxime groups displayed strong suppression effects on Co deposition and a suppression breakdown occurs upon the reduction of adsorbed Co-dioxime chelates7. This talk presents a study, where we used several dioxime additives like dimethylglyoxime (DMG), cyclohexane dioxime (CHD), and furil dioxime (FD) to investigate their impacts on Co nucleation process.
Figures 1 (a) and (b) show the chronoamperometries during the Co nucleation in presence of DMG and CHD, respectively. Two current peaks were observed, which are ascribed to a unique two-step nucleation behavior involving free cobalt cation and complexed cobalt chelates. Figure 1(c) shows the cyclic voltammetry of Co deposition with FD, where a concentration dependent suppression effect was observed. Figure 1(d) shows the normalized nucleation current transients numerically deconvoluted from the total currents. A progressive nucleation was observed. The results will be discussed in detail in conjunction with microscopic observations.

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Fig. 1 (a) Co nucleation process with the addition of 100 ppm DMG (b) Co nucleation process with the addition of 10 ppm CHD (c) The CV results with the addition of different concentration of FD (d) Normalized current transients with 10 ppm FD.

Figure 1