## 1 Introduction  
Recently, memory semiconductor device technologies have evolved to achieve fast switching, low-power consumption, and low memory bit-cost via the scaling-down of memory cells. Thus, two types of memory devices have been classified in terms of switching speed, power consumption, and cost per bit: dynamic random-access memory (DRAM) and three-dimensional (3D) NAND flash memory [1, 2, 3]. However, a 3D cross-point memory using phase-change random-access memory (PCRAM) has been proposed to generate a new storage memory in the memory hierarchy. Unlike DRAM, 3D cross-point PCRAM-based memory has demonstrated a nonvolatile memory characteristic with a fast operation speed of several hundred nanoseconds, and an excellent write-and-erase endurance cycle of \(>1\times 10^{8}\)[4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17]. In addition, a cross-point synaptic array using PCRAM has been extensively researched for neuromorphic hardware performing parallel computing, because PCRAM can supply a large resistance ratio to achieve a sufficient synaptic weight range, low-power consumption due to fast switching, and good scalability for synaptic array [18, 19, 20, 21]. In general, 3D cross-point PCRAM cells have been fabricated, and PCRAM-cells have a confined memory cell structure and a chalcogenide-based nonlinear-selector vertically stacked on the confined memory cell. Note that a confined memory cell structure with a vertical structure of the top electrode, PCRAM material filled in a confined hole, and bottom electrode are essential for minimizing the reset current. In addition, a chalcogenide-based nonlinear-selector stacked vertically on the confined memory cell is necessary for suppressing an integrated leakage current in a memory cell array. To fabricate a confined PCRAM-cell structure, a PCRAM material such as Ge\({}_{x}\)Sb\({}_{y}\)Te\({}_{x}\) or Ge or N\({}_{2}\) doped Sb\({}_{y}\)Te\({}_{x}\), etc., called a GST film, should be filled in the confined hole structure with a high aspect ratio of >10 [22]. Thus, sputtering followed by annealing, chemical vapor deposition (CVD), or atomic layer deposition (ALD) of a GST film in a confined-hole structure is utilized. Then, chemical-mechanical planarization (CMP) should be performed to eliminate the over-burdening of the GST film deposited on the confined hole structure and should be stopped as soon as a CMP stopping layer (i.e., Si\({}_{3}\)N\({}_{4}\) film surface) is exposed during the CMP process. It should be noted that CMP is conducted by a chemical reaction between the CMP slurry and the GST film surface as well as rubbing between nanoscale abrasives in the CMP slurry and the GST film surface. In particular, the GST films produced by CVD or ALD present a high chemical reactivity and extremely low mechanical hardness, so that the CMP of the GST film surface can easily result in corrosion of the GST film surface or surface-tensile-stress induced polishing-void after CMP. To avoid corrosion or polishing-void, the addition of an oxidizer (i.e., H\({}_{2}\)O\({}_{2}\)) in the GST film surface CMP slurry is essential, which can passivate the GST film surface by forming a chemical oxidizer layer on the GST film surface. However, an oxidizer significantly reduces the polishing-rate of the GST film surface and cannot completely prevent the generation of a corrosion or polishing-induced-void on the GST film surface after a CMP [22; 23]. In addition, the research has been reported for enhancing the GST film surface polishing-rate, presenting that the pH design of the GST film surface CMP slurry would be a key parameter to determine the GST-film surface polishing-rate [24; 25]. In our study, to simultaneously enhance the polishing rate of the GST film surface and suppress surface corrosion during CMP, a novel GST film surface CMP slurry was designed with the introduction of the Fenton reaction and the addition of a columbic-interactive corrosion inhibitor.