On the reaction mechanism of a hydroxyethylidene diphosphonic acid-based electrolyte for electrochemical mechanical polishing of copper

In the electrochemical mechanical polishing (ECMP) of copper, hydroxyethylidene diphosphonic acid (HEDP) can work with other water treatment agents to suppress electrolysis and smooth the metal surface. According to Faraday's law, a conventional operating potential lower than 4 V vs. SCE limits the material removal rate (MRR). To solve this problem, potentiodynamic corrosion, potentiostatic corrosion and ECMP experiments were conducted at higher potentials to study the feasibility of the process. The results show that at 6 V vs. SCE, the roughness of a copper wafer was improved, with a MRR of about 0.9 μm·min−1, higher than that obtained at the conventional potential. A sample of the barrier film on the copper surface was collected and analyzed by energy dispersive spectroscopy (EDS), Fourier transform infrared spectroscopy (FTIR) and mass spectrometry to investigate the reaction mechanism. It is shown that the copper ions ionized from the working electrode (WE) react with two HEDP molecules to form the coordination compound [CuL2]6−, then K+ combines with [CuL2]6− to produce the coordination compound [KCuL2]5−. Keywords: Hydroxyethylidene diphosphonic acid, Electrochemical mechanical polishing, Copper, Reaction mechanism