Research On Reactive Ion Etching Of Phase Change Material Cr-SbTe And Its Mechanism

Phase change random access memory(PCRAM) is a new type of non-volatile semiconductor memory technology with excellent comprehensive performance,which has shown good application prospects.The core of phase change memory is phase change.Phase change material chromium doped antimony telluride(Cr-SbTe),with high thermochemical stability and high crystallization speed,has the potential of replacing traditional phase change material germanium-antimony-telluride(GST).Etching of phase change material is the key technology for phase change memory(PCM) device fabrication.Therefore,this dissertation mainly explores and studies the etching process and etched damage mechanism of Cr-SbTe.In this paper,Cr-Sb Te film was deposited by magnetron sputtering system.Thickness,surface roughness and element composition under different deposition power were measured by FIB,AFM and EDS,respectively.Besides,the change of resistance under different temperature was measured.The optimized Cr-Sb Te film was characterized by XRD and Raman spectra.The flow ratio,working pressure and power of Ar/SF₆ and O₂/SF₆ on etching rate were investigated.Under the same etching conditions,the research shows that the etching rate of Ar/SF₆ is significantly higher than that of O₂/SF₆.The total flow rate was 50 sccm,and when the Ar/SF₆ flow ratio was 10:40,the maximum etching rate was 144.8 nm/min,leading to the minimum root mean square roughness of the etched film surface was 0.87 nm.As the pressure increases,the etching rate gradually decreases,and the optimal pressure is 10 mTorr.As the power increases,the etching rate first increases and then decreases.At a pressure of 10 mTorr and a power of 150 W,the etching rate is the largest,and the verticality of the sidewall is the best(approaching 90°).The selectivity of Ar/SF₆ to photoresist and SiO₂ was significantly higher than O₂/SF₆.The selectivity of Cr-SbTe to photoresist was up to 0.83,and to the SiO₂ was up to 3.3.Based on the above optimized process parameters,the chemical reactions during the etching process were analyzed.The Cr-SbTe films were characterized by XPS before and after etching,and the chemical state changes of Cr,Sb and Te elements were analyzed.It was found that Cr and Te elements were easy to be etched while Sb element was not easy to be etched.XPS depth analysis of the etched film surface shows that a thin layer of fluoride is formed on the film surface to protect the etched surface.The PCM device of phase change material Cr-SbTe was fabricated by etching process and its electrical performance was analyzed.This paper provides theoretical basis and experimental basis for the applications on Cr-SbTe etching process for phase change material to the fabrication of PCM.