## 3 Results and Discussion
The Ge\({}_{1}\)Sb\({}_{4}\)Te\({}_{5}\) film surface polishing rate slightly and linearly decreased from 90.2 to 67.2 nm/min when the corrosion inhibitor concentration increased from 0 to 0.09, as shown in Figure 3.7 In addition, the Si\({}_{3}\)N\({}_{4}\) film surface polishing-rate decreased significantly from 4.8 to 0.97 nm/min when the corrosion inhibitor concentration increased from 0 to 0.03 and then saturated at -0.9 nm/min for a further increase in the corrosion inhibitor concentration. The effect of the corrosion inhibitor  
Figure 3.8 Dependency of corrosion degree of Ge\({}_{1}\)Sb\({}_{4}\)Te\({}_{5}\) film surface on corrosion inhibitor (i.e., PEI) concentration after dipping of Ge\({}_{1}\)Sb\({}_{4}\)Te\({}_{5}\) film surface into slurries. (**a**) Potentiodynamic polarization curve of Ge\({}_{1}\)Sb\({}_{4}\)Te\({}_{5}\) film surface as a function of corrosion inhibitor concentration. (**b**) Dependencies of corrosion potential (\(\mathbf{E}_{\text{corr}}\)) vs. corrosion current density (\(\mathbf{I}_{\text{corr}}\)) on corrosion inhibitor concentration. on the suppression of CMP-induced corrosion was clearly observed by observing the SEM image of the Ge\({}_{1}\)Sb\({}_{4}\)Te\({}_{5}\) film surface after a CMP without a corrosion inhibitor, the relative corrosion-induced surface roughness (i.e., Rq of pixel intensity in SEM images) of the Ge\({}_{1}\)Sb\({}_{4}\)Te\({}_{5}\) film surface after a CMP was 14.8, as shown in (i) of Figures 8 and S5. As soon as a corrosion inhibitor (i.e., PEI) was added into the CMP slurry, the relative corrosion-induced surface roughness rapidly decreased from 3.24 to 2.25 when the corrosion inhibitor concentration changed from to 0.01 to 0.09-wt\({}^{\circ}\), as shown in the SEM images of (ii)-(vi) in Figure 3.9 In addition, we confirmed the Rq of the polished Ge\({}_{1}\)Sb\({}_{4}\)Te\({}_{5}\) film surface was \(\sim\)0.362 nm, which is a typical surface performance of CMP, as shown in Figure S6. These results indicate that the addition of a corrosion inhibitor (i.e., PEI) in the CMP slurry evidently suppresses the degree of corrosion-induced surface roughness. In general, a PRAM cell is fabricated with a confined hole structure with a high aspect ratio (i.e., 4-nm in diameter and 60.7-nm height), as shown in Figure 9[22; 23]. The polishing rate of the Ge\({}_{1}\)Sb\({}_{4}\)Te\({}_{5}\) film surface without a confined-hole structure PRAM-cell array pattern in Figure 8 would be lower than that of the Ge\({}_{1}\)Sb\({}_{4}\)Te\({}_{5}\) film surface with a confined-hole structure PRAM-cell array pattern, because the polishing-rate of the Ge\({}_{1}\)Sb\({}_{4}\)Te\({}_{5}\) film surface in a confined-hole structure PRAM-cell array pattern could be enhanced because of the confined memory cell structure-induced stress[22; 23]. Note  
Figure 3.0 Dependency of Ge\({}_{1}\)Se\({}_{4}\)Te\({}_{5}\)-, and Si\({}_{3}\)N\({}_{4}\) films polishing-rate on corrosion inhibitor (i.e., PEI) concentration. The background SEM images examined the presence of corrosion-induced pits on the Ge\({}_{1}\)Sb\({}_{4}\)Te\({}_{5}\) film surface after CMP. Figure 3.1 Dependency of chemical composition of Ge\({}_{1}\)Sb\({}_{4}\)Te\({}_{5}\) film surface on corrosion inhibitor (i.e., PEI) concentration after Ge\({}_{1}\)Sb\({}_{4}\)Te\({}_{5}\) film surface CMP. (**a**) NH\({}_{3}\)\({}^{+}\) and NH\({}_{2}\)\({}^{+}\) spectra. (**b**) Dependency of relative NH\({}_{3}\)\({}^{+}\) and NH\({}_{2}\)\({}^{+}\) peak intensity on corrosion inhibitor concentration of Ge\({}_{1}\)Sb\({}_{4}\)Te\({}_{5}\) film surface after CMP. that a higher stress leads to a higher polishing rate. Thus, the dependence of the recess degree on the corrosion inhibitor concentration was observed by cross (x)-sectional TEM images of the confined PRAM cells after CMP. In this confined memory-cell structure, a CMP should be automatically stopped as soon as a stopping layer (i.e., Si\({}_{3}\)N\({}_{4}\) layer) is exposed during CMP.