## 4 Conclusions  
To enhance the polishing rate of a Ge\({}_{1}\)Sb\({}_{4}\)Te\({}_{5}\) film surface and to minimize recess in a confined-hole structure PRAM-cell array pattern, the Fenton reaction was introduced, and a corrosion inhibitor (i.e., PEI) with protonated amine groups (i.e., NH\({}_{2}\)\({}^{+}\) and NH\({}_{3}\)\({}^{+}\)) was added to a Ge\({}_{1}\)Sb\({}_{4}\)Te\({}_{5}\) film surface CMP slurry. The Fenton reaction between the ferric-ionic catalyst (i.e., PDTA-Fe) and H\({}_{2}\)O\({}_{2}\) finally decomposed H\({}_{2}\)O\({}_{2}\) into dissolved O\({}_{2}\), OH\({}^{\bullet}\), and HO\({}_{2}\)\({}^{\bullet}\) in the slurry, as shown in Figure 10a. Then, the dissolved O\({}_{2}\), OH\({}^{\bullet}\), HO\({}_{2}\)\({}^{\bullet}\), and corrosion inhibitor (i.e., PEI) diffused and adsorbed on the Ge\({}_{1}\)Sb\({}_{4}\)Te\({}_{5}\) film surface as shown in Figure 10b. The adsorbed O\({}_{2}\), OH\({}^{\bullet}\), and HO\({}_{2}\)\({}^{\bullet}\) on the Ge\({}_{1}\)Sb\({}_{4}\)Te\({}_{5}\) film surface chemically oxidized the Ge\({}_{1}\)Sb\({}_{4}\)Te\({}_{5}\) film surface by forming Ge\({}_{2}\), Sb\({}_{2}\)O\({}_{3}\), and TeO\({}_{2}\) on the Ge\({}_{1}\)Sb\({}_{4}\)Te\({}_{5}\) film surface, as shown in Figure 10c. In particular, the higher sequence of chemical oxidation on the Ge\({}_{1}\)Sb\({}_{4}\)Te\({}_{5}\) film surface was followed by the forming of Ge\({}_{2}\), Sb\({}_{2}\)O\({}_{3}\), and TeO\({}_{2}\) and TeO\({}_{2}\). As soon as the chemically oxidized layer composed of GeO\({}_{2}\), Sb\({}_{2}\)O\({}_{3}\), and TeO\({}_{2}\) was produced on the Ge\({}_{1}\)Sb\({}_{4}\)Te\({}_{5}\) film surface, corrosion inhibitors with protonated amine groups (i.e., NH\({}_{2}\)\({}^{+}\) and NH\({}_{3}\)\({}^{+}\)) were attached on the Ge\({}_{1}\)Sb\({}_{4}\)Te\({}_{5}\) film surface by the attractive force between protonated amine groups of corrosion inhibitors and the negatively charged chemically oxidized Ge\({}_{1}\)Sb\({}_{4}\)Te\({}_{5}\) film surface, thus causing a passivation of the organic layer of the film surface and suppressing corrosion, as shown in Figure 10c. Afterward, colloidal  
Figure 9: Dependency of polishing-induced recess on corrosion inhibitor (i.e., PEI) concentration. The background TEM images observed the presence of polishing-induced recess on the Ge\({}_{1}\)Sb\({}_{4}\)Te\({}_{5}\) film surface after CMP. PEI concentrations of (**a**) 0, (**b**) 0.01, (**c**) 0.03, (**d**) 0.05, (**e**) 0.07, and (**f**) 0.09 wt%. silica abrasives polished off the chemically oxidized Ge\({}_{1}\)Sb\({}_{4}\)Te\({}_{5}\) film surface (having a passivated organic layer) via rubbing between the colloidal silica abrasives and the chemically oxidized Ge\({}_{1}\)Sb\({}_{4}\)Te\({}_{5}\) film surface; i.e., the CMP of the Ge\({}_{1}\)Sb\({}_{4}\)Te\({}_{5}\) film surface, as shown in Figure 10d. After several iterations of Figure 10a-d, the CMP automatically stopped as soon as the Si\({}_{3}\)N\({}_{4}\) film surface was exposed, since corrosion inhibitors with protonated amine groups (i.e., NH\({}_{2}\)\({}^{+}\) and NH\({}_{3}\)\({}^{+}\)) were preferentially attached to the highly negatively charged chemically oxidized Si\({}_{3}\)N\({}_{4}\) film surface, as shown in Figure 10e. It should be noted that the polishing rate selectivity between the chemically oxidized Ge\({}_{1}\)Sb\({}_{4}\)Te\({}_{5}\) film surface and the Si\({}_{3}\)N\({}_{4}\) film surface was 79:1, so that the patterned Ge\({}_{1}\)Sb\({}_{4}\)Te\({}_{5}\) film surface after CMP could attain a minimum recess (i.e., 0.8 nm). Therefore, the introduction of the Fenton reaction in a Ge\({}_{1}\)Sb\({}_{4}\)Te\({}_{5}\) film surface CMP slurry could significantly increase the polishing rate of the Ge\({}_{1}\)Sb\({}_{4}\)Te\({}_{5}\) film surface via efficient chemical oxidation (i.e., formation of GeO\({}_{2}\), Sb\({}_{2}\)O\({}_{3}\), and TeO\({}_{2}\)) on the Ge\({}_{1}\)Sb\({}_{4}\)Te\({}_{5}\) film surface.