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

Rather surprising behavior has been observed when aluminum (Al) is in conta ct with fluorine-doped silicon dioxide (FSG). With Al deposited onto FSG, x -ray photoelectron spectroscopy shows that there is only a very minor react ion at the interface, producing a small amount of AlF3. No fluorine is obse rved 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 ot her hand, with FSG deposited onto Al, the native aluminum oxide provides qu ite good protection against fluorine diffusion. By contrast, when pure Cu i s in contact with FSG, there is almost no interaction or fluorine diffusion . Various approaches to reducing fluorine diffusion into a metal are also d iscussed, including using a diffusion barrier (TiN, Ta, TaN) or a suitable plasma treatment of the FSG before metal deposition. (C) 1999 American Inst itute of Physics. [S0003-6951(99)01739-8].