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

Abstract

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 (Vth) drift than GeSe2 but exhibited the advantages of a higher threshold field, lower off-current, and smaller Vth fluctuation up to 106 cycles. Data availabilityThe data that has been used is confidential.