Study on the surface interaction mechanism, corrosion inhibition effect and the synergistic action of potassium oleate and fatty alcohol polyoxy ethylene ether on copper film chemical mechanical polishing for giant large scale integrated circuit

Abstract

As the feature size of integrated circuit drops down to 20–14 nm, cobalt (Co) is used as the barrier layer material for multilayer copper (Cu) wiring. The chemical mechanical polishing (CMP) process of Cu film has developed from a combined rough polishing and fine polishing to a one-step polishing, which needs to stop on the Co barrier layer. So the removal rate (RR) of Co should approach zero to meet the requirement of higher RR selection ratio of Cu and Co. Inhibitors in the Cu film slurry play an important role for controlling the RR during CMP process. In this paper, the anionic surfactant potassium oleate (PO) was selected as a key corrosion inhibitor in Cu film CMP to enhance the RR selection ratio of Cu and Co. The complexation and corrosion inhibition mechanisms between PO and Cu or Co were revealed by electrochemical measurements, X-ray photoelectron spectroscopy and scanning electron microscopy measurements. It was found that the rapid complexation of a small amount of PO with Co2+ could increase the Co RR. However, with a higher concentration of PO, the effective catalysis caused the conversion of cobaltous hydroxide to tricobalt tetraoxide, and thus resulted in a lower Co RR. With the addition of the nonionic surfactant called fatty alcohol polyoxy ethylene ether (JFCE), the morphology of the PO aggregates changes to spherical, which weakened the inhibiting effect of PO on Cu RR, and thus a higher Cu RR and RR selection ratio of Cu and Co was achieved. The synergistic action mechanism of PO and JFCE on Cu and Co surfaces was analyzed systematically. The present work provides an idea that surfactants are excellent candidates for metal inhibitors.