Experimental and Theoretical Investigation of the Copper (II)/Co Cementation Reaction

Abstract

Cobalt is a potential candidate as an adhesion layer in the copper metallization for its low resistivity and high thermal stability.(1) The electrodeposition of copper onto the cobalt substrate is a promising technique for the next generation interconnects. However, the cementation reaction of copper (II)/Co creates an irregular interface, and it’s not possible to apply the mature copper damascene plating technique.(2) In this work, we studied the Copper (II)/Co cementation reaction using a rotating disk electrode (RDE) and developed a continuum model to gain insight into the copper (II)/Co cementation reaction.Experimental section: a thin film of cobalt is firstly plated on the Pt RDE in a three-chamber cell filled with the electrolyte containing 50 mM CoSO4 and 0.5M H3BO3 (pH =2.6). A constant current is applied for a certain period of time (0.7 mA, 20 s) while the electrode is rotating at 700 rpm. The electrode is designated as Co/Pt electrode. After the deposition, the Co/Pt electrode is washed by ultrapure water and dried by nitrogen before it’s moved to another three-chamber cell. The electrode is immersed into the electrolyte containing 10mM CuSO4 and 50mM Na2SO4 while rotating at 900 rpm. The open-circuit potential is recorded in the whole process to identify the species and possible relations on the electrode surface.Figure 1 is the chronopotentiogram of a cobalt film reacting with copper(II) solution. As shown, fresh cobalt is replaced by the Cu in stage a, and a temporary equilibrium is reached in stage b, where the surface is a layer of newly formed metallic copper. A phase transition between copper and copper oxide is observed in stage c, and stage d represents a layer of CuOx, which is a dark color. (3) The intercept between stage and stage b will be used to extract the rate constant of the cementation reaction for modeling study. H.-S. Lu, J.-X. Wang, X. Zeng, F. Chen, X.-M. Zhang, W.-J. Zhang and X.-P. Qu, Electrochemical and Solid-State Letters, 15, H97 (2012).W.-Z. Xu, J.-B. Xu, H.-S. Lu, J.-X. Wang, Z.-J. Hu and X.-P. Qu, J Electrochem Soc, 160, D3075 (2013).J. Xiong and I. M. Ritchie, Hydrometallurgy, 16, 301 (1986). Figure 1