Study of Ge-rich GeSbTe etching process with different halogen plasmas

Chalcogenide materials based on GeSbTe (GST) ternary alloys are patterned using inductively coupled plasma in the manufacturing of phase change memories. The current process challenge is to maintain the GST composition and surface morphology to guarantee the memory performances. In this paper, the authors investigate the etching effects of different halogen plasmas (HBr, CF4, and Cl-2) on an optimized Ge-rich GST alloy. Using x-ray photoelectron spectroscopy (XPS) and plasma profiling time-of-flight mass spectrometry as complementary techniques, the authors noticed that the etched GST surface shows a stronger Te-rich damaged layer in the sequence of CF4 > Cl-2 > HBr. It is closely related to the higher affinity between halogen and GST elements in the sequence of Ge > Sb > Te. By comparing the etch rates with and without rf bias voltage, HBr etching is shown to be mainly related to the physical ion bombardment. On the contrary, Cl-2 plasma is mostly chemical and generates the roughest surface. The presence of a C-F passivation layer with CF4 plasma shows that both chemical reactivity and physical bombardment are necessary to etch efficiently the GST film. The oxidation of the HBr-etched GST surface was monitored by XPS as a function of several air exposure times. As a conclusion, the GST oxidation becomes critical after 24 h of air exposure. Published by the AVS.