Etch Damages of Ovonic Threshold Switch (OTS) Material by Halogen Gas Based-Inductively Coupled Plasmas

Abstract

The ovonic threshold switch (OTS) selector device is suitable for a phase-change random access memory (PRAM) requiring instantaneous high-output power due to the high-current density and high-speed operation. An amorphous chalcogenide-based compound composed of As-Te-Ge is a candidate for OTS materials and has excellent selector performances such as low leakage current, fast switching speed, scalability, and thermal stability. However, this material is known to suffer damage due to easy halogenation when exposed to halogen gas-based plasmas. In this study, the etch damages of OTS surface during the halogen gas based-inductively coupled plasma (ICP)-reactive ion etching (RIE) using CF4 and Cl2 were investigated. The OTS etched with Cl2 showed a higher etch rate compared to that with CF4. However, the surface roughness was lower for the OST etched with Cl2 than that etched with CF4. Also, the thickness of halogenated layer during the etching was also thinner for Cl2-etched OST than CF4-etched OST. Therefore, compared to CF4-etched OST, Cl2-etched OST was less damaged by the etching. In addition, it is found that, among the OST components of As, Te, and Ge, Ge was mostly halogenated while As and Te are not significantly halogenated during the etching.