Reactive ion etching of Si_xSb₂Te in CF₄/Ar plasma for nonvolatile phase-change memory device

SixSb2Te material system is novel for phase-change random access memory applications. Its properties are more outstanding than the widely used material Ge₂Sb₂Te₅. Etching process is one of the critical steps in the device fabrication. The etching characteristics of phase-change material Si_xSb₂Te were studied with CF ₄/Ar gas mixture by a reactive ion etching system. The changes of etching rate, etching profile and surface root-mean-square roughness resulted from variation of the gas-mixing ratio were investigated under constant pressure (50 mTorr) and applying power (200 W). Si_0.34Sb₂Te is with the highest phase-change speed and the lowest power consumption in the PCRAM memory among these compositions, which means it is the most promising candidate for the PCRAM applications. So the most optimized CF₄/Ar gas ratio for Si_0.34Sb₂Te was studied, the value is 25/25. The etching rate is 155 nm/min, and the selectivity of Si_0.34Sb ₂Te to SiO₂ is as high as 3.4 times. Furthermore, the smooth surface was achieved with this optimized gas ratio.