Fabrication and diffusion barrier properties of nanoscale Ta/Ta-N bi-layer

One of the most important processes in Cu metallization for ultra large scale integrated circuits (ULSI) is to fabricate better diffusion barrier. In this paper, Ta/Ta-N films were fabricated by dc magnetron reactive sputtering (DCMS) in N2/Ar ambient, then Cu/Ta/Ta-N/Si multi-structures were prepared in suite. The thin-film samples were rapid thermal annealed (RTA) at variational temperatures in N2 ambient. Alpha-Step IQ Profiler, four-point probe (FPP) sheet resistance measurer, atomic force microscope (AFM), scanning electron microscope (SEM), X-ray diffraction (XRD) and tape test were used to characterize the microstructure and diffusion properties of the thin-films. The results show that the nanoscale Ta/Ta-N thin-films have smooth surface, and the thermal stability and barrier performance are good. After 600 °C/300 s RTA, Ta (40 nm)/Ta-N (60 nm) thin-films can effectively block against Cu diffusion and keep good adhesion strength with Cu films. After higher temperature RTA process, Cu atoms penetrated through the barrier and reacted with silicon, the barrier fail.