Preparation and Properties Research of Ru0.26Sb2Te3 Alloy Target
Phase-change random access memory(PCRAM)is regard as the leading candidate for next generation electronic memory hierarchy.Sb-Te based alloys have received a lot of attention in recent years,because of its high crystalline growth velocity and poten-tial as phase change material application.However,the practical application of such materials is severely hindered by several bottle-necks,such as poor thermal stability,low crystallization temperature.It has been shown that Ru doped Sb2Te3 phase change material is expected to improve the low crystallization temperature and poor thermal stability of Sb2Te3 to meet the stable operation requirements of phase-change memory stability.The preparation of Ru doped Sb2Te3 alloy targets was studied in this paper.Three different raw mate-rial systems were compared:(1)Ru0.26Sb2Te3 alloy powder,(2)Ru+Sb+Te mixed powder and(3)Ru+Sb2Te3 mixed powder,in which the atomic ratio of each element was Ru∶Sb∶Te=0.26∶2∶3.For Ru0.26Sb2Te3 alloy powder system,the powder was prepared by mixing elemental powders of Ru,Sb and Te in a quartz tube and sealing in vacuum,then Ru-doped Ru0.26Sb2Te3 alloy powder was pre-pared by vacuum melting,mechanical crushing and sieving.The raw material systems of Ru+Sb+Te and Ru+Sb2Te3 mixed powder were obtained by ball milling three elemental powders of Ru,Sb and Te,the powder of Ru and the alloy powder of Sb2Te3,respective-ly.Sputtering targets using these powder systems were then prepared by vacuum hot pressing method under 540 ℃ for 40 Mpa and 3 h.The phase structure,composition,microstructure and element distribution of the targets were characterized by means of X-ray diffrac-tion(XRD),chemical titration,scanning electron microscope(SEM),energy dispersive analysis(EDS)and confocal laser scanning microscope(CLSM).The actual density of the targets was measured by Archimedes Principle,and the relative density of the target was obtained by comparing with the theoretical density.The results showed that by controlling the input ratio of three elemental powder during vacuum melting,the composition of both the alloy powder and alloy target sample could accord well with the theoretical stoichio-metric ratio,in which Ru,Sb and Te contents of alloy powder were 5.40％,36.11％and 58.49％(atom fraction),and Ru,Sb and Te contents of alloy target were 5.29％,37.06％and 57.65％(atom fraction),respectively.Most of the diffraction peaks of the alloy pow-der corresponds to the characteristic peaks of Sb2Te3phase,three major diffraction peaks were(015),(0015)and(1010),which meant Sb2Te3 was formed during the melting process.The characteristic peaks of RuTe2 phase with three major peaks of(111),(120)and(200)were also visible,and no elemental Ru peak was observed.The main phases of the target were matrix phase Sb2Te3 and RuTe2,and RuTe2 phase was uniformly distributed in the matrix phase.By comparing the lattice constant of Sb2Te3 powder and Ru0.26Sb2Te3 powder,the addition of Ru element had no significant effect on the lattice constant of Sb2Te3 phase.After doping Ru ele-ment,the lattice constant of Sb2Te3 phase changed from a=0.4264 nm and c=3.0421 nm to a=0.4264 nm and c=3.0419 nm.From the confocal laser scanning microscope picture,it could be seen that the microstructure distribution on the surface and the cross-sectional of the target were basically the same,and there were merely no defects such as porosity.The element distribution mapping results showed that Ru,Sb and Te elements were uniformly distributed on the surface of the target.The density of this target measured by Ar-chimedes Principle was 6.62 g·cm-3,and the relative density reached 99.83％,which could meet the film sputtering application re-quirements.The main phase of Ru0.26Sb2Te3 ternary target prepared by Ru+Sb+Te mixed powder and Ru+Sb2Te3 mixed powder raw ma-terial system was also Sb2Te3 phase,with Ru existed in the target in the form of elemental phase.The major XRD peaks of target pre-pared by Ru+Sb+Te mixed powder raw material system was(015),(1010)and(110),which were different from that of Ru0.26Sb2Te3 alloy powder and Ru+Sb2Te3 mixed powder raw material system,indicating the preferred orientation of Sb-Te alloy in the Ru+Sb+Te mixed powder might be different from Ru0.26Sb2Te3 alloy powder and Ru+Sb2Te3 mixed powder.From the surface element distribution mapping,it could be seen that compared with Ru0.26Sb2Te3 alloy powder raw material system,Ru element in two mixed powder raw ma-terial system was relatively concentrated in some regions,and was not completely dispersed in the entire matric phase.The density of the targets obtained from Ru+Sb+Te mixed powder and Ru+Sb2Te3 mixed powder raw material system was 6.55 and 6.50 g·cm-3,with the relative density of 98.79％and 98.04％respectively,which were lower than the target prepared by Ru0.26Sb2Te3 alloy powder raw material system.Therefore,the ternary alloy target prepared by the raw material system of Ru0.26Sb2Te3 alloy powder was more likely to be used in the preparation of Ru-Sb-Te series phase change memory thin films.
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