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

Abstract

Phase change random access memory (PCRAM) is one of the most industrially applicable memory devices because of its advantages such as non-volatility, high speed, scalability, and low power consumption. Ovonic threshold switch (OTS) materials are used in selector devices in PCRAM circuits and are generally composed of chalcogenide compounds. In this study, etch characteristics of OTS material composed of Ge-As-Te has 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 of the OTS material, but the formation of nitride compound and the increased roughness were observed on the OTS surface. In the case of CH4 plasma, due to the carbon on the OTS surface, a polymer layer was deposited. Even though H2 showed the better surface smoothness due to the no surface residues or compounds on OTS surface related to carbon or nitrogen, the etch rates were lower than NH3. In this presentation, the effects of various hydrogen-based gases on the etch characteristics of OTS material will be discussed in details.