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Texture and phase transformation of sputter-deposited metastable Ta films and multilayers

1996; Elsevier BV; Volume: 275; Issue: 1-2 Linguagem: Inglês

10.1016/0040-6090(95)07043-5

1879-2731

R. Hoogeveen, M. Moske, H. Geisler, K. Samwer,

Electronic Packaging and Soldering Technologies

Two different structures of Ta are known: the bulk bcc structure of α-Ta (a = 0.33058nm) and the metastable tetragonal β-Ta phase (a = 0.534nm, c = 0.994nm). The metastable phase is mainly observed in sputter-deposited thin films and a dependence on film thickness and deposition conditions have been reported. In our study we investigated the structure and the crystallographic orientation of d.c.-magnetron sputtered Ta films using wide-angle X-ray diffraction after preparation and after annealing. Ta films were deposited onto different underlayer materials (Al, SiO2 and Cu). For TaCu multilayers the single layer thickness and the sputter parameters are varied. It is observed that the Ta structure after deposition mainly depends on the substrate or underlayer material. β-Ta is always observed after sputtering onto SiO2 or (111)-textured Cu, with the orientation of the Ta grains depending on the Ta-layer thickness, whereas α-Ta is observed on an (111) Al underlayer. Therefore, the bulk equilibrium phase only seems to be forced by an epitaxial relation. During annealing up to 700 °C the (100)-oriented grains of β-Ta change their orientation and the metastable gb-phase transforms into the equilibrium α-phase with (110) texture. The temperature for structural transformation decreases with increasing Ta layer thickness.