# Electolytically Ionized Abrasive-Free CMP (EAF-CMP) for Copper
## 3 Results and Discussion
### Effect of Chemical Component Concentration on Material Removal in EAF-CMP
The _CR_ also increased as the citric acid concentration increased (Figure 11b). When citric acid is 0 M in the chemical solution, the _CR_ is 0.04 mpy, and when 0.02 M of citric acid is added, the _CR_ increases dramatically to 5.44 mpy. The increased citric acid concentration in the chemical solutions of EAF-CMP appears to increase the probability of binding citric acid and Cu ions, increasing the etch rate and average MRR. Figure 10: CMP results as a function of citric acid concentration; (**a**) MRR distribution and (**b**) average MRR and WIWNU. Corrosion inhibitors form a Cu complex film, which helps planarize patterns by controlling excessive corrosion by the oxidizer in the CMP slurry. Figure 12 shows the change in MRR and its distribution according to the BTA concentration. The average MRR tended to decrease as the BTA concentration of the chemical solution increased. The average MRR was 364.1, 300.9, 196.0, and 142.5 nm/min, respectively, when the chemical solution contained 0.05 wt%, 0.10 wt%, 0.15 wt%, and 0.20 wt% of BTA. Compared to the results of changes in H\({}_{2}\)O\({}_{2}\) and citric acid concentration, the changes in the WIWNU were small, with the lowest being at 0.01 wt% and 0.15 wt%. As the BTA content increased, the _CR_ and etch rate tended to decrease because the Cu-BTA complex layer inhibited the dissolution of the Cu by the chemical solution (Figure 13) [23]. Figure 11: Etch rate and corrosion rate as a function of citric acid concentration; (**a**) etch rate and (**b**) corrosion rate. In this study, a comparative study of AF-CMP and EAF-CMP was conducted, and it was confirmed that the MRR can be improved by the electrolytic ionization of chemical solutions for AF-CMP. Electrolytically ionized chemical solutions seem to produce a more mechanically easy-to-remove chemically reacted layer and higher chemical dissolution of Cu than conventional chemical solutions using AF-CMP. Figure 14 shows the probable material removal mechanism of EAF-CMP. The oxidation reaction of the electrolytically ionized chemical solution and the Cu generates Cu ions, which are combined with citrate ions in the chemical solution and removed from the surface of the Cu in the form of Cu-citrate ions. BTA in the chemical solution combines with the Cu ions to form a Cu-BTA complex layer on the surface of the Cu film and is removed by the asperities of the polishing pad, resulting in mechanical material removal. MRR increased with increases in concentrations of H\({}_{2}\)O\({}_{2}\) and citric acid used as an oxidizer and complexing agent; however, MRR decreased with an increase in the concentration of BTA used as a corrosion inhibitor. Figure 12: CMP results as a function of BTA concentration; (**a**) MRR distribution and (**b**) average MRR and WIWNU. The proposed EAF-CMP in this study will be able to increase the efficiency of AF-CMP, and further research on chemical solution and material removal phenomena will be required. Furthermore, it seems that more diverse electrode materials and modularization are needed to be able to increase the efficiency of AF-CMP. Figure 14: Material removal mechanism of EAF-CMP. Figure 13: Etch rate and corrosion rate as a function of BTA concentration; (**a**) etch rate and (**b**) corrosion rate. of nozzle-containing electrodes are needed for a more efficient electrolytic ionization of the chemical solution.