Study on Hydrogen-Based Reactive Ion Etching of Ovonic Threshold Switch (OTS) Materials for Phase Change Memory Devices

Abstract

Ovonic threshold switch (OTS) materials are used in selector devices for phase change random access memory (PcRAM) circuits and are generally composed of chalcogenide compounds. In this study, etch characteristics of OTS material composed of Ge-As-Te have been investigated using reactive ion etching (RIE) by hydrogen-based gases such as H2, CH4, NH3, etc. Among the investigated hydrogen-based plasmas, NH3 showed the highest etch rate due to the high vapor pressures of the hydrides, but the formation of nitride compounds and the increased roughness were observed on the OTS surface. In the case of CH4+NH3 (1:1 ratio) plasma, the OTS material could be etched at high OTS etch rates without the formation of nitrogen compounds and without increasing the chemical and physical damage on the OTS surface through the formation of volatile CN-related compounds.