Etch damages of ovonic threshold switch (OTS) material by halogen gas based-inductively coupled plasmas

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.