Mechanism of residue formation on Ge-rich germanium antimony tellurium alloys after plasma etching

In phase-change random access memory (PCRAM) applications, the germanium antimony tellurium alloy (GST) is patterned using halogen etching in inductively coupled plasma reactors. This paper focuses on the surface state evolution of an optimized Ge-rich GST material after plasma etching. Four hours after etching, big dome-shaped residues are observed on PCRAM structures. Their number and size increase with the time of air exposure. X-ray photoelectron spectroscopy and energy-dispersive x-ray spectroscopy analyses reveal an important germanium oxidation on the surface with residues. Their formation is then investigated. Complementary analyses highlight that the moisture environment has a catalytic effect on the residue formation. Based on this study, a detailed mechanism responsible for residue formation is proposed.