Conformal Formation of (GeTe₂)_(1–x)(Sb₂Te₃)_x Layers by Atomic Layer Deposition for Nanoscale Phase Change Memories

Phase change random access memory appears to be the strongest candidate for next-generation high density nonvolatile memory. The fabrication of ultrahigh density phase change memory (≫1 Gb) depends heavily on the thin film growth technique for the phase changing chalcogenide material, most typically containing Ge, Sb and Te (Ge–Sb–Te). Atomic layer deposition (ALD) at low temperatures is the most preferred growth method for depositing such complex materials over surfaces possessing extreme topology. In this study, [(CH 3 ) 3 Si] 2 Te and stable alkoxy-Ge (Ge(OCH 3 ) 4 ) and alkoxy-Sb (Sb(OC 2 H 5 ) 3 ) metal–organic precursors were used to deposit various layers with compositions lying on the GeTe 2 –Sb 2 Te 3 tie lines at a substrate temperature as low as 70 °C using a thermal ALD process. The adsorption of Ge precursor was proven to be a physisorption type while other precursors showed a chemisorption behavior. However, the adsorption of Ge precursor was still self-regulated, and the facile ALD of the pseudobinary solid solutions with composition (GeTe 2 ) (1-x) (Sb 2 Te 3 ) x were achieved. This chemistry-specific ALD process was quite robust against process variations, allowing highly conformal, smooth, and reproducible film growth over a contact hole structure with an extreme geometry. The detailed ALD behavior of binary compounds and incorporation behaviors of the binary compounds in pseudobinary solid solutions were studied in detail. This new composition material showed reliable phase change and accompanying resistance switching behavior, which were slightly better than the standard Ge 2 Sb 2 Te 5 material in the nanoscale. The local chemical environment was similar to that of conventional Ge 2 Sb 2 Te 5 materials.