CHF3/O2-Based Plasma Reactive Ion Etching of GeTe for Nonvolatile Phase Change Memory

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The reactive-ion-etching (RIE) characteristics of phase change material GeTe in CHF3/O2 plasma for back end of nonvolatile phase change memory devices were investigated in this paper. The etch rate and surface root-mean-square (RMS) roughness of crystalline GeTe and amorphous GeTe films were studied with various etching parameters, such as gas mixture ratio, chamber gas pressure, and power. It is found that the etch rate first increases with the increasing concentration of O2 and get at peak value 68.5 nm/min at 12% O2/(CHF3+O2), then decreases from 12% to 20% of O2 fraction. The surface RMS roughness slightly increases with the increasing oxygen content. By changing the gas pressure, the etch rate of GeTe films increases approximately linearly with increasing gas pressure up to 50 mTorr. In addition, the etch rate increases approximately linearly with increasing power below 400 W. The XPS spectra shows that some non-volatile GeFx, GeOx, TeFx, and TeOx by-products were left on the etched film surface. From these results of etched TiN films and GeTe films, the result of RIE with one step recipe shows the formation of under-cut on the profile of etched film. However, the result of RIE with two steps recipe shows better vertical characteristic and few residues were left on the profile of etched film.