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Reactive ion etching of Si2Sb2Te5 in CF4/Ar plasma for a nonvolatile phase-change memory device

Phase change random access memory (PCRAM) is one of the best candidates for next generation nonvolatile memory, and phase change Si2Sb2Te5 material is expected to be a promising material for PCRAM. In the fabrication of phase change random access memories, the etching process is a critical step. In this paper, the etching characteristics of Si2Sb2Te5 films were studied with a CF4/Ar gas mixture using a reactive ion etching system. We observed a monotonic decrease in etch rate with decreasing CF4 concentration, meanwhile, Ar concentration went up and smoother etched surfaces were obtained. It proves that CF4 determines the etch rate while Ar plays an important role in defining the smoothness of the etched surface and sidewall edge acuity. Compared with Ge2Sb2Te5, it is found that Si2Sb2Te5 has a greater etch rate. Etching characteristics of Si2Sb2Te5 as a function of power and pressure were also studied. The smoothest surfaces and most vertical sidewalls were achieved using a CF4/Ar gas mixture ratio of 10/40, a background pressure of 40 mTorr, and power of 200 W.