Research On Etching Flattening Of Three-dimensional Stacked Phase Change Memory

As memory planar size miniaturization technology approaches its physical limits and Moore's Law slows down,the 3D XPoint memory,a three-dimensional stacking technology based on phase change memory(PCRAM),has attracted widespread attention.With its fast IO access,high throughput and non-volatile performance,it becomes a major breakthrough in the history of storage technology.However,the technology is still immature and faces serious challenges in terms of manufacturing cost,process complexity and device structure in order to achieve mass production and improve market competitiveness.The existing 3D XPoint memory based on horizontal electrode stacking does not solve the problem of electrode height difference caused by multi-dimensional stacking,which limits the development of 3D XPoint memory to higher-level stacking integration technology.Under this background,this study designs a process optimization scheme to flatten the insulating layer of 3D XPoint memory to achieve higher density memory device design.The main research elements are as follows:(1)In this dissertation,the basic principles of etching process are introduced.Based on the needs of this study and the properties of reactive ion etching(RIE)such as controllable etching rate and better surface morphology after etching,the memory production process flow is optimized to achieve etching flattening using RIE.(2)To achieve the best performance,the etching rates of both Ge₂Sb₂Te₅ and SiO₂should be similar and the etched surface roughness should be small.In this dissertation,a specific experimental scheme is designed to adjust the etching conditions parameters such as gas ratio,RF power and pressure in RIE with EUV,magnetron sputtering and PECVD processes to produce samples under different etching conditions.(3)The etching results of RIE under two gas environments,CHF₃/Ar and CHF₃/O₂,were studied by AFM and SEM semiconductor characterization techniques and the effects of various etching conditions on the etching results were analyzed.The best etching results were obtained when using CHF₃/O₂ mixed gas etching,and the etching conditions were 20%O₂ concentration,150W RF power,and 50mtorr pressure,at which the etching rates of both materials were about 53nm/min and the surface roughness RMS were 1.33nm and 0.97nm,respectively.This result not only ensured the similar etching rates,but also obtained smooth surface,satisfying the requirement of flattening.(4)A first-principles analysis of the chemical process of the etching reaction of Ge₂Sb₂Te₅ phase change material was carried out using the Dmol³ module of Material Studio software to analyze the fluorination reaction process.