| AVS 65th International Symposium & Exhibition | |
| Plasma Science and Technology Division | Wednesday Sessions |
| Session PS+EM-WeA |
| Session: | Advanced BEOL/Interconnect Etching |
| Presenter: | Ernest Chen, University of California, Los Angeles |
| Authors: | N.D. Altieri, University of California, Los Angeles E. Chen, University of California, Los Angeles J.P. Chang, University of California, Los Angeles S.W. Fong, Stanford University C.M. Neumann, Stanford University H.-S. Wong, Stanford University M. Shen, Lam Research Corporation T.B. Lill, Lam Research Corporation |
| 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.
Understanding the effects of plasma processing as well as post-processing damage of the phase change material (PCM) utilized in PCRAM is crucial to ensuring proper device performance. The studies presented herein focus on the behavior of Ge2Sb2Te5 (GST-225) in conjunction with H2 and CH4 discharges as well as the roles of O2 and N2 through the use of a custom-built integrated ion beam chamber, inductively coupled plasma reactor, and in-situ x-ray photoelectron and quadrupole mass spectrometers.
Etch and gas phase reaction byproducts for single element Ge, Sb, and Te as well as GST-225 in hydrogen and methane have been identified through the use of quadrupole mass spectrometry and optical emission spectroscopy. X-ray photoelectron spectroscopy has been used to characterize surface bonding states and film composition across a wide parameter space, including low and high pressures as well as varying feed gas compositions.
Methane and hydrogen-based discharges were identified as capable GST etchant chemistries, resulting in rates up to 80 nm/min; however, the post-processing film composition was found to be strongly dependent on the chosen etch chemistry. Hydrogen radicals were identified as the dominant etchant species and resulted in the preferential removal of Sb and Te at low (15 mTorr) and high (75 mTorr) pressure conditions through the formation of volatile hydride products. Post-processing surface analysis indicated a substantial decrease in Sb and Te concentration from their initial 22 and 55 atomic percent to 3 and 4 atomic percent as well as an accumulation of Ge on the post-etch surface. Tuning of the etch chemistry was further explored through the use of auxiliary N2 in order to modify the etch rate and preserve the starting 2:2:5 stoichiometry crucial to proper PCRAM device performance.