Crystal Phase Transition of Atomic Layer Deposited Antimony Telluride Thin Films with Thickness and Substrate-Dependent Orientations

Abstract

With the advances for the vertical-NAND flash memories, phase-change memory (PCM) has attracted enormous interests as one of the next-generation storage-class memory, combined with ALD technologies.1 In general, the PCMs are composed of complex chalcogenide alloys which can be tuned by ternary or quaternary alloys such as Ge-Sb-Te (GST).2 Among chalcogenides for PCMs, antimony telluride (Sb2Te3) has been considered as a candidate with a high crystallization speed. While it is the basic component of the GST, Sb2Te3 has received relatively less attention due to its low thermal stability and electrical resistivity. However, in recent years, the stacking and forming heterostructures composed of chalcogenides including Sb2Te3 has been found to have huge potential as PCM.3 Since the out-of-plane orientations of heterostructured layers is important, the atomic-scale observation of film growth and crystallinity formation of Sb2Te3 is required, including substrate dependency. Though, most of studies have focused on the formation of GST alloys, not the growth of ALD Sb2Te3 itself. Herein, we aimed to investigate the atomic-scale thin film growth and phase transition of ALD Sb2Te3 thin films. Comparatively, thin film growth modes of ALD Sb2Te3 on amorphous and crystalline substrates were studied by observing transformation of crystal structures. On SiO2, predominant amorphous phases at initial growth stage were observed, followed by polycrystalline island growth with randomly oriented grains. However, on crystalline W, the highly out-of-plane (00l) orientations and layer-by-layer growth was found. Furthermore, the consequent changes in electrical resistivity of ALD Sb2Te3 were observed to examine the correlations with substrate-dependent film orientations.