## 3 Results and Discussion
When 1.5 and 5.0 wt% picolinic acid were added to the slurry, the grains of tungsten remained well because the amounts of adsorbed picolinic acids were sufficient to suppress tungsten dissolution. In general, corrosion (i.e., dissolution) of tungsten mainly occurs at the grain boundary with high thermodynamic activation energy. However, since picolinic acid protects the reaction active site via adsorbing to the tungsten grain boundary through covalent coordination bonding, the surface roughness could be dramatically improved. The R\({}_{\text{a}}\) values obtained from AFM and SEM images were well correlated. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multicolumn{2}{c}{**Langmuir Constant**} & \multicolumn{4}{c}{**Freundlich Constant**} \\ \hline \(\mathbf{Q_{m}}\) [mg/m\({}^{2}\)] & \(\mathbf{b}\) [L/mg] & \(\mathbf{R^{2}}\) & \(\mathbf{K_{F}}\) & \(\mathbf{1/n}\) & \(\mathbf{R^{2}}\) \\ \hline
0.399 & 0.009 & 0.994 & 0.017 & 0.479 & 0.825 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Langmuir and Freundlich constants for the adsorption of picolinic acid onto the tungsten oxide surface. As shown in Figure 3, the surface of tungsten films after the CMP test were analyzed by AFM and SEM. In the absence of picolinic acid, grains remained despite the application of CMP process. The persistence of the grains result from dissolution in the valleys between the grains as the tops are polished. Using 0.5 wt% of picolinic acid failed to remove the grains, as the picolinic concentration was not sufficient to prevent dissolution in the tungsten valleys. On the other hand, the grains were well removed with 1.5 wt% picolinic acid, and R\({}_{\text{a}}\) decreased from 17.3 nm to 7.8 nm after CMP process. This result indicates that 1.5 wt% picolinic acid is sufficient for the protection of the tungsten valleys between the grains during the CMP such that the topography was smoothed. The removal and dissolution rates of tungsten as a function of picolinic acid concentration were calculated and are shown in Figure 4. The removal rate of the tungsten films gradually decreased from 120 to 85 A/min with increasing concentration of picolinic acid up to 1.5 wt% due to the adsorption of picolinic acid. Additionally, at this picolinic acid concentration, the topography of tungsten, as represented by the R\({}_{\text{a}}\) value, was well removed. On the other hand, the tungsten dissolution rate dramatically decreased from 90 to  
Figure 3: (**a**) Atomic force microscopy (AFM) and (**b**) scanning electron microscope (SEM) images of tungsten films after the CMP evaluation as a function of picolinic acid concentration. Figure 2: (**a**) Atomic force microscopy (AFM) and (**b**) scanning electron microscope (SEM) images of tungsten films after the dipping test as a function of picolinic acid concentration. 11 A/min as picolinic acid concentration increased up to 1.5 wt%, while a high R\({}_{\text{a}}\) value was maintained. This result indicates that the excessive tungsten dissolution was suppressed. Both the removal and dissolution rates decreased up to a picolinic acid concentration of 1.5 wt% and showed almost the same results at 5.0 wt% because the adsorption of picolinic acid onto the surface of tungsten oxide saturates at this concentration. These results are in good agreement with the adsorption isotherm simulations.