Metal/fluorinated-dielectric interactions in microelectronic interconnections: Rapid diffusion of fluorine through aluminum

Abstract

Rather surprising behavior has been observed when aluminum (Al) is in contact with fluorine-doped silicon dioxide (FSG). With Al deposited onto FSG, x-ray photoelectron spectroscopy shows that there is only a very minor reaction at the interface, producing a small amount of AlF3. No fluorine is observed in the bulk of the Al film, but fluorine diffuses readily through the Al even at room temperature and reacts at the free metal surface. On the other hand, with FSG deposited onto Al, the native aluminum oxide provides quite good protection against fluorine diffusion. By contrast, when pure Cu is in contact with FSG, there is almost no interaction or fluorine diffusion. Various approaches to reducing fluorine diffusion into a metal are also discussed, including using a diffusion barrier (TiN, Ta, TaN) or a suitable plasma treatment of the FSG before metal deposition.