With the continuous miniaturization of integrated circuit (IC) devices, Co is recognized as the most prospective alternative to Cu as an interconnecting metal. In the IC processing, Co surfaces need to be flattened. This paper conducts dynamic polishing experiments and static corrosion experiments on the electrical, chemical, and mechanical factors involved in the cobalt electrochemical mechanical polishing (ECMP). Then, the impact and proportion of individual and combining factors on Co ECMP are quantitatively analyzed. The experimental results show that mechanical action plays a primary role in Co ECMP, compared with individual chemical or electrical action. The ratio of individual mechanical, chemical, and electrical action proportion is 50.46%, 11.17%, and 6.20%, respectively. However, chemical and electrical assistance with mechanical action can achieve twice efficiency and high-quality polishing of Co. For instance, the ratio of mechanical-chemical or electrical-chemical-mechanical cooperation is 72.05% or 100% respectively. In addition, polarization curves, EDS, and XPS are used to analyze the Co ECMP process and products. And atomic-level mechanism analysis is performed for each factor. The results indicate that in Co ECMP, the oxides formed on the Co surface are mainly CoO, Co(OH)₂, and Co₃O₄. The oxides react with the complexing agents to form loose and porous Co-BTA complexes. Mechanical, chemical, and electrical factors collaborate to constantly form and remove Co-BTA, achieving rapid material removal and obtaining atomic-level smooth surfaces.

Ultrasonic-assisted chemical mechanical polishing (UA-CMP) can greatly improve the sapphire material removal and surface quality, but its polishing mechanism is still unclear. This paper proposed a novel model of material removal rate (MRR) to explore the mechanism of sapphire UA-CMP. It contains two modes, namely two-body wear and abrasive-impact. Furthermore, the atomic force microscopy (AFM) in-situ study, computational fluid dynamics (CFD) simulation, and polishing experiments were conducted to verify the model and reveal the polishing mechanism. In the AFM in-situ studies, the tip scratched the reaction layer on the sapphire surface. The pit with a 0.22 nm depth is the evidence of two-body wear. The CFD simulation showed that abrasives could be driven by the ultrasonic vibration to impact the sapphire surface at high frequencies. The maximum total velocity and the air volume fraction (AVF) in the central area increased from 0.26 to 0.55 m/s and 20% to 49%, respectively, with the rising amplitudes of 1–3 μm. However, the maximum total velocity rose slightly from 0.33 to 0.42 m/s, and the AVF was nearly unchanged under 40–80 r/min. It indicated that the ultrasonic energy has great effects on the abrasive-impact mode. The UA-CMP experimental results exhibited that there was 63.7% improvement in MRR when the polishing velocities rose from 40 to 80 r/min. The roughness of the polished sapphire surface was R_a = 0.07 nm. It identified that the higher speed achieved greater MRR mainly through the two-body wear mode. This study is beneficial to further understanding the UA-CMP mechanism and promoting the development of UA-CMP technology.