The Study on Electromechanical Polishing of Cu Metal and Its Electrochemical Charateristics

Unlike conventional chemical mechanical polishing (CMP), electrochemical mechanical polishing (ECMP) enables virtually zero downforce (< 0.5 psi), which can manage the weak mechanical strength of low-k dielectrics. In addition, in this new voltage-induced ECMP technology, we can use slurries without abrasives, which can not only evade the procedure of post-cleaning but also avoid the defect caused by abrasives. In this study, we focus on the efficacy and corrosion kinetics during Cu ECMP in H3PO4-based slurries by operating parameters of applied potential, downforce, and rotated speed. Also, we discuss the electrochemical effect of adding abrasives or adding inhibitor of PEG. By performing electrochemical measurements such as polarization curves and open-circuit potentials, we investigate the relationship between electrochemical corrosion and mechanical abrasion during Cu ECMP. Furthermore, surface morphological analysis after ECMP was carried out by atomic force microscopy (AFM) to acquire the roughness of Cu surface before and after ECMP process. The experimental results show that applied potential is the main operation parameter during Cu ECMP. As applied potential increases from 0.1V to 0.8V, it would increase the removal rates of Cu, causing thinner passive film, and the roughness of Cu surface would also increase from 12.63 nm to 57.54 nm, lowering the planarity or the polished Cu surfaces. Besides, on the research of adding abrasives, the outcome shows that adding abrasives may not support mechanical abrasion and therefore it is not a effective way to improve the planarity after Cu ECMP. Moreover, we confer the viscosity effect and the change after adding PEG 600. The experimental results indicate that inhibitor of PEG would be adsorbed on the Cu surface, causing denser Cu oxide layer. Adding inhibitor in H3PO4 slurries effectually hinder the corrosion reaction, attaining high planarity and polishing performances.