Growth and Electrical Characteristics of PE-ALD Germanium Sulfide for 3D Cross-Point Memory

The 3D cross-point memory, known to contain chalcogenide material-based ovonic threshold switching (OTS) selector, is bringing new changes to the memory hierarchy of DRAM and NAND flash memory. The cross-point memory of current planar 3D structures, meanwhile, is already expected to limit scaling in terms of number of critical masks and normalized cost, so it is necessary to prepare a vertical 3D structures [1]. Atomic layer deposition (ALD) process, which is essential to realize vertical 3D structures, has been mostly studied for phase change materials (PCM) based on GeSbTe but OTS selector research is still in its early stage. So, we have studied plasma enhanced-ALD (PE-ALD) of germanium sulfide (GeS) films containing sulfur chalcogenide element with higher optical bandgap than Te and Se for low off current OTS selector for larger array implementation [2] [3]. The PE-ALD of GeS amorphous chalcogenide films was synthesized using commercially available GeCl4 precursor with H2S plasma reactant. The Ge1S2 film was identified quantitative composition and impurities through AES depth profile analysis, and excellent thermal stability up to 600 ℃ was studied by In-situ high temperature X-ray diffraction (HT-XRD). And PE-ALD Ge1S2 has confirmed the superior step coverage in the vertical 3D structure through FIB-TEM compared to chemical vapor deposited GeS film. In addition, the devices of the 50 nm bottom electrode contact size using PE-ALD Ge1S2 films demonstrated OTS characteristic with of remarkable high threshold field 3.0 MV/cm, and low normalized off-current of 25 nA at half threshold voltage. The achievement of PE-ALD research on simple binary Ge1S2 amorphous chalcogenide will contribute to development the future 3D cross-point memory scaling. Acknowledgments This paper was result of the research project supported by SK Hynix Inc. Reference [1] T. Kim and S. Lee, “Evolution of Phase-Change Memory for the Storage-Class Memory and Beyond,” IEEE Trans. Electron Devices, vol. 1, pp. 1–13, 2020. [2] C. C. Wu, C. H. Ho, J. Y. Wu, S. L. Lin, and Y. S. Huang, “Characterization of Ge(Se1-xSx)2 series layered crystals grown by vertical Bridgman method,” J. Cryst. Growth, vol. 281, no. 2–4, pp. 377–383, Aug. 2005. [3] J. W. Park et al., “Optical properties of pseudobinary GeTe, Ge2 Sb2 Te5, GeSb2 Te4, GeSb4 Te7, and Sb2 Te3 from ellipsometry and density functional theory,” Phys. Rev. B - Condens. Matter Mater. Phys., vol. 80, no. 11, Sep. 2009.