Study On High Aspect Ratio Etching Process Of Ge₂Sb₂Te₅ Phase Change Material

Phase change memory(PCM)is considered to be one of the most promising next-generation memories due to its advantages such as low operating power consumption,fast read and write speed,non-volatility,high density,and compatibility with CMOS technology.With the continuous advancement of microelectronic process technology nodes,the size reduction of PCM has become more and more difficult,and the development of three-dimensional stacked 3D PCM has become an important means to improve the storage density of devices.During the preparation of 3D PCM,the aspect ratio of the device increases as the number of stacked layers increases.How to achieve high aspect ratio etching has become a key challenge in the 3D PCM process,but the current research on the etching process of phase change materials is extremely Lack,it also faces problems such as lack of high-selectivity mask materials and poor etching topography.To this end,this paper takes the most typical phase change material Ge₂Sb₂Te₅(GST)as an example,and conducts a systematic study on its etching process.Through the design of mask material and optimization of process parameters,the high aspect ratio etching of GST is realized.The mechanism is analyzed.The main results of the paper are as follows:(1)An Inductively Coupled Plasma(ICP)etching process based on grating patterns is designed,and a Si₃N₄hard mask scheme for GST high aspect ratio etching is proposed.The grating pattern is used for the etching experiment,which is convenient for observing the morphology of the cross-section after etching.The result shows that the RIE etching process does not obtain good steep sidewalls,which may be due to the high pressure in the reaction chamber of the instrument and its inaccuracy Therefore,the ICP process that can precisely control the gas pressure is preferred;the experiment further found that the commonly used photoresist is used as a mask,which is relatively small compared with GST etching,and it is difficult to achieve sufficient depth etching.Therefore,a hard mask based In the GST etching scheme,the Si₃N₄ hard mask material that is higher than the GST etching selection is selected,and the etching effect of high aspect ratio is realized.(2)The ICP process parameters of GST were optimized,and high aspect ratio etching up to 7:1 was realized,and simulation verification was carried out.Using Cl₂/Ar to etch GST,explore the influence of gas flow,power,pressure,etching time and line width size on the etching effect during the etching process,and analyze the etching mechanism and chemical residue in depth in combination with(X-ray photoelectron spectroscopy)XPS.Optimize the etching conditions to achieve an etching aspect ratio of up to 7:1,which is the maximum value of the phase change material etching aspect ratio reported in the literature,and the sidewall of the etching pattern is steep and the surface roughness is small.Finally,the Athena process module in the simulation software Silvaco Tcad is used to simulate and verify the GST etching results of different etching times and different sizes.It is obtained that the etching rate will decrease with the extension of the etching time and the reduction of the graphic size.The results are consistent with the experimental rules.