Direct evidence of reactive ion etching induced damages in Ge2Sb2Te5 based on different halogen plasmas

Chalcogenide glasses based on Ge-Te-Sb are processed using reactive ion etching (RIE) in the fabrication of phase change memory (PCM). These materials are known to be halogenated easily and apt to be damaged when exposed to halogen gas based plasmas which can cause severe halogenation-induced degradation. In this paper, we investigate the RIE induced damage of popular phase change material Ge2Sb2Te5 (GST) in different halogen based plasmas (CF4, Cl2 and HBr) highly diluted by argon. After blanket etching, results of scanning electron microscopy and atomic force microscopy directly showed that the surface of Cl2 etched samples were roughest with a Ge deficient damaged layer. X-ray photoelectron spectroscopy was performed to investigate the chemical shift of constituent elements. Selected scans over the valence band peaks of Te 3d revealed that electrons were transferred from chalcogenide to halogen and the highest halogenation was observed on the GST etched by CF4. The GST films masked with patterned TiN were also etched. High-resolution transmission electron microscopy and surface scan directly showed the line profile and the damaged layer. Almost vertical and smooth sidewall without damaged layer makes HBr a promising gas for GST etch in the fabrication of high-density memory devices.