## 3 Results and Discussion
This result indicates that the introduction of the Fenton reaction in the slurry could suppress the static corrosion via chemical passivation (i.e., oxidation), in which the dissolved O\({}_{2}\) and radicals (i.e., HO\({}_{2}\)* and OH\({}^{\bullet}\)) chemically reacted with Ge, Sb, and Te atoms in the Ge\({}_{1}\)Sb\({}_{4}\)Te\({}_{5}\) film surface. As mentioned earlier, the dissolved O\({}_{2}\) and O\({}_{2}\)\({}^{-}\) radicals were produced by the Fenton reaction between the Fe\({}^{3+}\) catalyst and H\({}_{2}\)O\({}_{2}\) in the CMP slurry. Figure 4: Dependency surface roughness of Ge\({}_{1}\)Sb\({}_{4}\)Te\({}_{5}\) film surface on ferric-ionic catalyst (i.e., PDTA-Fe) concentration after dipping of Ge\({}_{1}\)Sb\({}_{4}\)Te\({}_{5}\) film surface into slurries. The background AFM images estimated the presence of corrosion-induced pits and corrosion degree (i.e., Rq) on the Ge\({}_{1}\)Sb\({}_{4}\)Te\({}_{5}\) film surface after dipping. Figure 3: Dependency of static etch rate (SER) of Ge\({}_{1}\)Sb\({}_{4}\)Te\({}_{5}\) film surface on ferric–ionic catalyst (i.e., PDTA–Fe) concentration after dipping of Ge\({}_{1}\)Sb\({}_{4}\)Te\({}_{5}\) film surface into slurries. The background SEM images investigated the presence of corrosion-induced pits on the Ge\({}_{1}\)Sb\({}_{4}\)Te\({}_{5}\) film surface after dipping. Fenton Reaction Mechanism for Enhancing Polishing Rate and Suppressing Corrosion on the Ge\({}_{1}\)Sb\({}_{4}\)Te\({}_{5}\) Film Surface during CMP  
The chemical passivation (i.e., oxidation) on the Ge\({}_{1}\)Sb\({}_{4}\)Te\({}_{5}\) film surface via the Fenton reaction was characterized by chemical composition analysis via XPS of the Ge\({}_{1}\)Sb\({}_{4}\)Te\({}_{5}\) film surface dipping into the slurries at 70 \({}^{\circ}\)C for 1 min. Without the Fenton reaction, the relative XPS peak intensities were at 1220-eV (i.e., GeO\({}_{2}\)) and 1218-eV binding energy (i.e., Ge) were 40,232.6 and 23,321.9 a.u., as shown in Figure 5a. When the catalyst PDTA-Fe concentration increased from 0.01 to 0.05-wt%, the relative XPS peak intensity of GeO\({}_{2}\) increased exponentially from 54,128.1 and 158,677 a.u., while for Ge, it slightly decreased from 17,040.3 to 6467.8 a.u., as shown in the inset of Figure 5a. This result implies that the dissolved O\({}_{2}\) and radicals (i.e., HO\({}_{2}\)\({}^{\bullet}\) and OH\({}^{\bullet}\)) via the Fenton reaction between the Fe\({}^{3+}\) catalyst and H\({}_{2}\)O\({}_{2}\) can oxidize the Ge\({}_{1}\)Sb\({}_{4}\)Te\({}_{5}\) film surface by producing GeO\({}_{2}\), and the chemical oxidation degree of the Ge\({}_{1}\)Sb\({}_{4}\)Te\({}_{5}\) film surface linearly increased with the catalyst (i.e., PDTA-Fe) concentration. In addition, without the Fenton reaction, the relative XPS peak intensities at 539.5-eV binding energy (i.e., Sb\({}_{2}\)O\({}_{3}\) of Sb3d 3/2) and 530-eV binding energy (i.e., Sb\({}_{2}\)O\({}_{3}\) of Sb3d 5/2) were 108,718.2 and 307,888.6 a.u., as shown in Figure 5b. Both peaks linearly increased from 141,982 to 294,615.2 and 307,888.6 to 623,299.1 a.u., respectively, when the PDTA-Fe concentration increased from 0.01 to 0.05-wt%. Otherwise, the XPS peak intensities at 538-eV (i.e., Sb of Sb3d 3/2) and 528.2-eV (i.e., Sb of Sb3d 5/2) binding energy were independent of the catalyst PDTA-Fe concentration. This result also means that the Fenton reaction could oxidize easily the Ge\({}_{1}\)Sb\({}_{4}\)Te\({}_{5}\) film surface by producing a chemically oxidized layer (i.e., Sb\({}_{2}\)O\({}_{3}\)). Furthermore, without the Fenton reaction, the relative XPS peak intensities at 586-eV (i.e., TeO\({}_{2}\) of Te3d 3/2) and 576-eV (i.e., TeO\({}_{2}\) of Te3d 5/2) binding energies were 190430.6 and 274607 a.u., respectively, as shown in Figure 5c. Although, the catalyst PDTA-Fe concentration increased from 0.01 to 0.05-wt%, both peak intensities very slightly increased with the PDTA-Fe concentration.