Preparation And Properties Of Al_0.7Sb₂Te₃ Alloy Target Applied For Phase Change Memory

Al-Sb-Te phase-change thin film is the research hotspot of phase-change memory due to high compatibility with CMOS and good thermal stability at present.Nowadays,Prepared by the method of multi-target co-sputtering,Al-Sb-Te phase-change thin film will get good thermal and electricity properties for high speed storage.But the composition uniformity of thin film is not good,and the designed composition is hard to complete accurately for thin film.These problems can be solved hopefully by using the multi-component single target for sputtering.So how to design or optimize the preparation process of multi-component single target,and how to characterize systematically properties representing the target's quality are important topics in the area of phase-change memory.Based on research progress of Sb-Te series phase-change material and the synthesizing experiment results of binary alloys,we adopt the component with atom ratio of 0.7:2:3.Al-Sb-Te synthetic powder and alloy target used for depositing Al_0.7Sb₂Te₃ thin film were prepared respectively by vacuum solid phase synthesis and sintering-HIP method.Phase structure of powder and phase structure,microstructure,element distribution and valence composition of Al-Sb-Te target were characterized by XRD,FESEM,metallographic microscope,EDS and XPS,which can evaluate the quality of target and analyze the existence form of Al in AST synthesis powder and alloy target.Firstly,we discuss physicochemical properties of Al,Sb,Te and theirs related compounds,and analyse the results of reaction thermodynamics and dynamics.These studies contribute to promoting the mixing and pressing process,and designing the vacuum solid phase synthesis temperature and corresponding holding time of AlSb,Sb₂Te₃,Al₂Te₃ and AST powder.The results indicate the synthesis difficulty of binary alloy ranking from small to large is Sb₂Te₃,AlSb and Al₂Te₃.Compared with the mixed powder composed of Al,Sb and Te,phase structure is changed obviously in AST synthesis powder,which means the main phase is Sb₂Te₃ and a little amount of Al exists.Besides,the lattice constants of main phase Sb₂Te₃ with Al doped are different from the binary alloy powder Sb₂Te₃.Lattice constant a is almost invariable,but lattice constant c decreases from 31.443 A to 30.438 A and the volume V decreases by 0.016%.Secondly,the preparation and properties of AST alloy target are studied.With using AST synthesis powder as raw material,AST alloy target with relatively density of 99.6%is prepared by sintering-HIP method.The results of FESEM show that the surface and crossover of the target have basically similar microstructure and the dual-phase composition including Al_0.1Sb₂Te₃ matrix and Aluminum dispersoids are obviously formed in these two areas.Meanwhile,two phases are closely combined with 2?3 ?m transitional region.Results of XPS indicates that from outside to inside,with the depth varies from 0 to 405.9 nm,the main valence of Al transits gradually from compound state of Al2O3 to elementary substance state.And when the erosion depth is 405.9 nm,the valence composition of Al contains a little amount of AlSb compound state,valence composition of Sb comes from Sb₂Te₃,Sb₂O₃ and AlSb,and valence composition of Te only comes from Sb₂Te₃.XPS analysis of the depth etched by 405.9 nm shows the Aluminum of Al_0.1Sb₂Te₃ matrix influences target organization structure by forming effectively AlSb.