Investigation of the behavior of benzimidazole and its derivatives as corrosion inhibitors for cobalt in alkaline medium

Abstract

Cobalt, as a barrier layer between copper and dielectric during the integrated circuit (IC) copper interconnect process, is commonly applied to stop diffusion each other below the 14 nm technology node. And the corrosion problem is a significant focus of research in the cobalt barrier chemical mechanical polishing process. Corrosion inhibitors are essential additives in polishing slurries to reduce corrosion and improve polishing performance. In this paper, the inhibition behavior of benzimidazole and its two derivates (2-hydroxybenzimidazole and 2-aminobenzimidazole) for cobalt in alkaline medium was investigated. The static corrosion rates of cobalt decreased with rising inhibitors concentration and the corrosion inhibition efficiencies (IE) exceeded 90 % when the concentration of the three inhibitors was above 5 mM. Under conditions of sufficient inhibitor concentration, the removal rates of the dynamic polishing process decreased, and 10 mM was determined as the optimal concentration due to achieving the required removal rate (100–300 Å/min). The contact angles and polishing results for cobalt immersed in solutions with corrosion inhibitors showed that the three inhibitors led to the more hydrophobic cobalt surface, indicating the passivation film formation. The results of potentiodynamic polarization and electrochemical impedance spectroscopy experiments exhibited the similar inhibition characteristics for cobalt according to the decreased corrosion current density (icorr), the increased polarization resistance (Rp) and the reduced capacitance of the interface (Cdl). The inhibition efficiency for cobalt is in the order of 2-aminobenzimidazole > 2-hydroxybenzimidazole > benzimidazole. The adsorption of the three inhibitors obeyed the Langmuir’s adsorption isotherm. The corrosion inhibition is attributed to the adsorption of inhibitors molecules through the combination of physical and chemical adsorption on the cobalt surface.