For phase-change memory beyond the 30 nm design rule, chemical mechanical planarization ͑CMP͒ performing at a high polishing rate, reasonable selectivity, and no corrosion-induced pits is essential for planarizing nitrogen-doped polycrystalline Ge 2 Sb 2 Te 5 ͑GST͒ deposited on the confined memory cell structure. We develop a new alkaline slurry added with KMnO 4 used as an oxidizer. The alkaline slurry added with 0.3 wt % KMnO 4 has a polycrystalline GST film polishing rate of 5200 Å/min, a polishing rate selectivity between polycrystalline GST and SiO 2 film of 100:1, and no corrosion-induced pit. In addition, polycrystalline GST film CMP using the alkaline slurry added with KMnO 4 is observed to follow a cyclic reaction polishing mechanism.Materials based on Ge-Sb-Te ternary alloy have been extensively researched as data storage media for phase-change memory ͑PCM͒ because of their large difference in electrical resistance between amorphous and polycrystalline states. 1-4 PCM is a unique nonvolatile memory that has write and erase times of several tens of nanoseconds. 5 Among the Ge-Sb-Te-based materials, Ge 2 Sb 2 Te 5 ͑GST͒ has been widely adopted and investigated because of its fast crystallization speed and low energy requirements for the phase change. 5,6 Particularly, nitrogen-doped GST film has been demonstrated to reduce reset current and enhance endurance characteristics. 6-8 Due to a strong thermal crosstalk effect between adjacent cells as the device design rule scales down to less than 30 nm, PCM cell structure has evolved from a conventional T-shaped structure to a confined one. 9 As a unique global planarization method used in the semiconductor manufacturing process, chemical mechanical planarization ͑CMP͒ has been introduced to planarize the GST film surface after gap filling by GST in the confined structure. 9-11 Here, the deposited GST is preferred in a polycrystalline state rather than an amorphous one to achieve a higher speed and a wider sensing margin. Moreover, polycrystalline GST is inevitably used to avoid incomplete contact between electrodes and amorphous GST because an amorphous GST material shrinks by 5-7% volume as it switches from an amorphous to crystalline state by thermal process. 12 Therefore, a CMP slurry with a high polishing rate, a high polishing rate selectivity between GST and surrounding insulator films, and good surface quality of the GST film needs to be developed to achieve the successful CMP process in a PCM fabricated with the confined cell structure, as shown in Fig. 1.However, the polishing rate of a polycrystalline GST film is considerably lower than that of an amorphous GST film, 13,14 and thus, an oxidizer needs to be added to the CMP slurry to enhance the chemical reaction rate of polycrystalline GST film. In our previous study, we reported on the CMP performance in areas such as polishing rate and selectivity for a polycrystalline GST film polished in the alkaline slurry with hydrogen peroxide ͑H 2 O 2 ͒ up to 3.0 wt %. We found that polycrystalline GST film ...

In the fabrication of cross-point phase-change-memory-cells through atomic-layer-deposition of Ge-doped SbTe (Ge-ST) film followed by chemical-mechanical-polarization (CMP), a remarkable surface tensile stress was generated, originating from the surface stress induced by the pad down force and the surface structure tensile stress in a confined memory-cell structure. It was maximized at the position of the Si 3 N 4 -film spacer where the curvature becomes zero. The maximized surface tensile stress produced polishing induced voids via the generation mechanism of the stress corrosion cracking. The generation frequency and nanoscale size of the polishing induced voids rapidly increased at the maximum surface tensile stress during CMP. Then, they slightly decreased and saturated when the surface tensile stress reduced during further CMP. A design of a spacer using a SiO 2 -film spacer rather a Si 3 N 4 -film spacer could prevent the generation of the polishing induced voids, confirming that the generation mechanism of the polishing induced voids is associated with the stress corrosion cracking.

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