# Electolytically Ionized Abrasive-Free CMP (EAF-CMP) for Copper
## 3 Results and Discussion
### Effect of Chemical Component Concentration on Material Removal in EAF-CMP  
In this section, the effects of the components of the EAF-CMP chemical solution on the MRR and WIWNU of Cu will be discussed. As mentioned in Section 2.2, the chemical solution for EAF-CMP contains H\({}_{2}\)O\({}_{2}\), citric acid, and BTA as oxidizers, complexing agents, and corrosion inhibitors, respectively. Figure 8 shows the MRR distribution (Figure 8a), average MRR, and WIWNU (Figure 8b) of Cu as a function of H\({}_{2}\)O\({}_{2}\) concentration in the chemical solution. To determine the effect of changes in the H\({}_{2}\)O\({}_{2}\) concentration on the MRR, the citric acid and BTA concentration \begin{table}
\begin{tabular}{c c c} \hline \hline
**Parameters** & **AF-CMP** & **EAF-CMP** \\ \hline Abrasive & No & No \\ Electrolytic ionization & No & Yes \\ Average friction force (kgf) & 5.509 & 7.946 \\ MRR (nm/min) & 236.9 & 303.9 \\ WIWNU (\%) & 3.7 & 3.2 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Comparison between AF-CMP and EAF-CMP. Figure 6: CMP results of AF-CMP and EAF-CMP; (**a**) MRR distribution and (**b**) average MRR and WIWNU. Figure 7: Friction force as a function of processing time in AF-CMP and EAF-CMP. were fixed at 0.01 M and 0.1 wt%, and the H\({}_{2}\)O\({}_{2}\) concentration varied from 0 wt% to 5 wt%. Without H\({}_{2}\)O\({}_{2}\) in the chemical solution, the average MRR was 31.4 nm/min and WIWNU was 30.4%. The average MRR continued to rise until the H\({}_{2}\)O\({}_{2}\) concentration was increased to 5 wt%, and the average MRR improved to 303.9 nm/min and WIWNU to 3.2%. In Cu CMP, H\({}_{2}\)O\({}_{2}\), used as an oxidizer, oxidized the surface of the Cu, helping to create a mechanically easy-to-remove surface [37,38]. Copper etching occurs when Cu ions and complexing agents are combined during the oxidation of Cu. Figure 9a shows the changes in the etch rate of the Cu according to the H\({}_{2}\)O\({}_{2}\) concentration. Without H\({}_{2}\)O\({}_{2}\) in the chemical solution, the etch rate of the Cu was 5.6 nm/min. The etch rates at H\({}_{2}\)O\({}_{2}\) concentrations of 1 wt%, 3 wt%, and 5 wt% were 24.8, 35.1, and 43.4 nm/min, respectively. Figure 9b shows that \(CR\) continued to increase from 0.31 mpy to 5.44 mpy as the H\({}_{2}\)O\({}_{2}\) concentration increased from 0 wt% to 5 wt%. Thus, as the H\({}_{2}\)O\({}_{2}\)  
Figure 8: CMP results as a function of H\({}_{2}\)O\({}_{2}\) concentration; (**a**) MRR distribution and (**b**) average MRR and WIWNU. concentration increased, the etch rate of the Cu increased because of the electrolytically ionized chemical solution, resulting in an increase in the MRR. As shown in Figure 10, citric acid, which acts as a complexing agent in the Cu EAF-CMP, also increased the average MRR as its concentration in the chemical solution increased. During the experiment on the effect of citric acid, H\({}_{2}\)O\({}_{2}\) concentration and BTA concentration were fixed at 3 wt% and 0.1 wt%, respectively, and the citric acid concentration was changed from 0 M to 0.02 M. As shown in Figure 10a, when the citric acid content was 0 M, the average MRR was 27.7 nm/min, and the addition of 0.005 M citric acid to the chemical solution greatly increased the average MRR to 288.4 nm/min. When the citric acid concentration in the chemical solution was 0.01 M and 0.02 M, the average MRR gradually increased to 300.9 and 391.6 nm/min. WIWNU decreased with the addition of citric acid, having the lowest value of 2.6% at 0.01 M, which slightly increased at 0.02 M to 5.9%. As in  
Figure 9: Etch rate and corrosion rate as a function of H\({}_{2}\)O\({}_{2}\) concentration; (**a**) etch rate and (**b**) corrosion rate. experiments with H\({}_{2}\)O\({}_{2}\) concentration changes, the etch rate of Cu tends to increase with increasing citric acid concentration in electrolytically ionized chemical solutions. As shown in Figure 11a, while citric acid concentration increased from 0 M to 0.02 M, the etch rate of the Cu increased from 3.0 nm/min to 83.5 nm/min.