Dresden 2003 – scientific programme

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DS: Dünne Schichten

DS 20: Schichteigenschaften

DS 20.1: Talk

Thursday, March 27, 2003, 10:15–10:30, GER/38

Diffusion phenomena in ultrathin Ta-based barrier layers for Cu metallization — •René Hübner, Michael Hecker, Norbert Mattern, and Klaus Wetzig — Leibniz Institute for Solid State and Materials Research Dresden, Helmholtzstr. 20, D-01069 Dresden, Germany

Due to its higher electromigration resistance and lower electrical resistivity, Cu is used as metallization material for integrated circuits. To prevent the diffusion of Cu into Si and SiO₂ substrates of microelectronic devices, effective diffusion barriers are needed. Because of their high thermal stability, Ta-based layers are suited for this purpose. Nevertheless, at elevated temperatures, the diffusion of different atomic species becomes possible within Cu metallization systems.

For our experiments, Ta-based single layers (10 nm) as well as graded barriers were radio-frequency magnetron sputtered from a Ta or Ta₅Si₃ target for different N₂ flows onto oxidized silicon wafers and capped with a 50 nm thick Cu film. By means of X-ray diffraction, glow discharge-optical emission spectroscopy and transmission electron microscopy, various diffusion phenomena, like N redistribution within graded Ta-TaN barriers, were observed after annealing the samples at different temperatures. Investigations to reduce or inhibit the different diffusion processes were also done. Ta diffusion out of the barrier layer through the Cu to the sample surface, for instance, can be prevented by capping the metallization with a silicon oxide film, and the stability of barrier layers against Cu diffusion into the substrate is enhanced by the application of amorphous Ta-Si-N layers instead of crystalline Ta films.