Interfacial stability of electroplated copper on a 5nm ruthenium film supported by silicon, Cu∕(5nmRu)∕Si, was investigated using Rutherford backscattering and high-resolution analytical electron microscopy. Transmission electron microscopy (TEM) imaging shows that a 5nm Ru film is amorphous in contrast to the columnar microstructures of thicker films (20nm). Direct Cu plating on a 5nm Ru film yielded a homogeneous Cu film with over 90% plating efficiency. It is demonstrated that 5nm Ru can function as a directly plateable Cu diffusion barrier up to at least 300°C vacuum anneal. TEM reveals an interlayer between Ru∕Si, which expands at the expense of Ru upon annealing. Electron energy loss spectroscopy analyses show no oxygen (O) across the Cu∕(5nmRu)∕Si interfaces, thereby indicating that the interlayer is ruthenium silicide (RuxSiy). This silicidation is mainly attributed to the failure of the ultrathin Ru barrier at the higher annealing temperature.
The effect of ash chemistries, N2/H2 and H2, on time-dependent dielectric breakdown (TDDB) lifetime has been investigated for Cu damascene structure with a carbon-doped CVD ultra low-k (ULK, k=2.5) intermetal dielectric. Two failure modes, interfacial Cu-ion-migration and Cu diffusion through the bulk intermetal ULK were attributed to the TDDB degradation for the H2 ash.The interfacial Cu-ion-migration was the only dominated failure mode for the N2/H2 ash. The nitrogen species in the N2/H2 plasma proved to be capable of forming a nitrided protection layer on the surface of the ULK. This nitrided layer suppressed further plasma damage during the ash process and thus lessened the TDDB degradation by preventing Cu diffusion through the bulk ULK.
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