| AVS 66th International Symposium & Exhibition | |
| Plasma Science and Technology Division | Tuesday Sessions |
| Session PS+EM-TuA |
| Session: | Advanced BEOL/Interconnect Etching and Advanced Memory and Patterning |
| Presenter: | Ernest Chen, University of California, Los Angeles |
| Authors: | E. Chen, University of California, Los Angeles N.D. Altieri, University of California, Los Angeles C.M. Neumann, Stanford University S.W. Fong, Stanford University H.-S.P. Wong, Stanford University M. Shen, Lam Research Corporation T.B. Lill, Lam Research Corporation J.P. Chang, University of California, Los Angeles |
| Correspondent: | Click to Email |
The manipulation of the amorphous to crystalline phase transition observed in chalcogenide glasses for non-volatile memory applications has been studied for many years since its initial conception. However, only recently has innovation in both materials development and memory device architecture enabled phase change random access memory (PCRAM) to become a promising candidate for applications such as neuromorphic computing. Ternary chalcogenide glasses consisting of germanium, antimony, and tellurium are widely used in PCRAM applications, and Ge2Sb2Te5 (GST-225) will be the focus of this study.
Understanding the effects of plasma processing on the phase change material (PCM) utilized in PCRAM is crucial to ensuring proper device performance. The studies presented in this talk utilize a custom-built integrated system equipped with ion beam processing, downstream plasma processing, quadrupole mass spectrometry, optical emission spectroscopy, and x-ray photoelectron spectroscopy capabilities. The samples are prepared by sputtering from a stoichiometric GST-225 target. Prior studies have examined the behavior of GST-225 when exposed to different components of ambient exposure (N2, O2, and H2O) as well as H2 and CH4 discharges and identified H2 and CH4 as capable GST etchants.
It is known that ambient exposure will cause a GST-225 layer to be oxidized in the first several nanometers, and this oxidized layer has different properties from the bulk of the GST-225 film and may also behave differently from the bulk material when exposed to plasma processing. Initial studies with ex-situ XPS analysis indicate that H2 can etch GST-225 with approximately 5% change in composition (5% increase in Ge, 5% decrease in Sb, approximately 0% change in Te) and a significant change in the ratio of 0+ to X+ (non-oxidized to oxidized) bonding states between the oxidized surface and the etched surface. In order to distinguish the effects of plasma processing on the oxidized layer and the bulk material, a custom-built downstream plasma processing chamber integrated with an XPS chamber is used. This system allows for the study of the surface states of GST-225 post-processing without any inadvertent effects from ambient conditions that may complicate ex-situ XPS analysis.