Superconformal Copper Electroplating on an Ultrathin Cobalt Seed in an Acidic Copper Sulfate Electrolyte

• Published in: Journal of the Electrochemical Society 2022-08, Vol.169 (8), p.82508
• Main Authors: Liu, Y., Brogan, L. J., Rigsby, M. A., Huie, M. M., Opocensky, E. C., Spurlin, T. A., Reid, J. D.
• Format: Article
• Language: English
• ISSN: 0013-4651; 1945-7111
• DOI: 10.1149/1945-7111/ac862d

Cu electroplating on an ultrathin Co seed has been developed for superconformal filling of advanced interconnects, in an acidic CuSO 4 electrolyte containing plating additives, i.e., halide, suppressor, accelerator, and leveler. A suppressor-halide adlayer is found to play a bifunctional role in both suppressing Cu growth and inhibiting Co dissolution. Corrosion inhibition is attributed to adsorption of hydrophobic suppressor molecules on a halide-terminated Co surface that blocks water from interacting with Co, thereby retarding the formation of Co(OH) + , a corrosion immediate with which hydronium from the electrolyte would react to form soluble Co 2+ . With enhanced suppression, Co loss is mainly confined to the removal of native Co oxides in acid. Correspondingly, galvanic Cu deposition forms a monolayer shortly after immersion at open-circuit potential, becoming self-limited with growth of a second layer over the next 20 s as dynamic surface processes make more underlying Co available for the displacement reaction. Growth of the first Cu layer is controlled by the receding of native oxides in an exponential-decay manner. Native Co oxides, if not removed, promote Cu protrusions in electroplating. The proposed process produces void-free fill on a 22 nm wide feature with a Co liner about 20 Å thick after fill.