Composition-controllable growth of GeTex thin films via combined atomic layer deposition and chemical vapor deposition

Abstract

Ovonic threshold switching (OTS) selectors are gaining significant attention as essential components for high-density memory applications, enabling high reliability of crossbar arrays by effectively suppressing sneak currents. However, achieving uniform and compositionally precise thin films of OTS materials using atomic layer deposition (ALD) remains challenging because of the requirements for Te-rich stoichiometry and the sensitivity to process conditions. This study presents a composition-controllable plasma-enhanced atomic layer deposition (PEALD) process for GeTe_x thin films utilising Ge(OC₂H₅)₄ and Te(Si(CH₃)₃)₂, with NH₃ plasma introduced to enhance reaction efficiency. The co-injection of NH₃ plasma resulted in different saturation levels for Ge and Te, facilitating the integration of a supercycle. Specifically, three supercycles were developed, consisting of one to three Te half-cycles for each Ge half-cycle, resulting in Te-rich thin films as the number of Te half-cycles increased. Substrate dependence observed on Si and W substrates was resolved by incorporating a passivation layer. The electrical properties were assessed by fabricating devices with W top and bottom electrodes. While stoichiometric GeTe_x films demonstrated resistive switching behavior, Te-rich compositions exhibited characteristic OTS performance. This study provides insights into the deposition method of Te-rich GeTe_x thin films, addressing current challenges in the advancement of future high-density memory devices.