Amorphous Ge-Se-S chalcogenide alloys via post plasma sulfurization of atomic layer deposition GeSe for ovonic threshold switch applications

For the future scaling of 3D cross-point (X-point) memory, it is necessary to implement atomic layer deposition (ALD) of chalcogenides for ovonic threshold switch (OTS) applications. We investigated ternary Ge-Se-S amorphous chalcogenide alloys based on ALD process, motivated by the expectation of low off-current and stable OTS behavior by partially replacing S in binary Ge-Se. Ge-Se-S alloys were synthesized by post-deposition sulfurization of ALD GeSe₂ thin films. Especially, we investigated the growth characteristics and film properties of ALD GeSe₂ using HGeCl₃ precursors with Se(SiMe₃)₂ together with density-functional theory (DFT) calculations. By changing the temperature and the low-temperature plasma sulfurization time, the compositions of 10-nm-thick Ge-Se-S thin films were controlled along the GeSe₂-Ge₂S pseudo-binary line in ternary phase diagram. It was confirmed that the Ge₅Se₃S₂ alloys maintained an amorphous phase and excellent step coverage, similar to ALD GeSe₂. Finally, we compared the OTS electrical characteristics of 10-nm-thick ALD GeSe₂ with Ge₅Se₃S₂ amorphous chalcogenide thin films in a mushroom-type device with a 50-nm bottom electrode. The novel Ge₅Se₃S₂ had a slightly larger threshold voltage (V_th) drift than GeSe₂ but exhibited the advantages of a higher threshold field, lower off-current, and smaller V_th fluctuation up to 10⁶ cycles. Data availability: The data that has been used is confidential.