Low temperature inorganic chemical vapor deposition of Ti-Si-N diffusion barrier liners for gigascale copper interconnect applications

A new low temperature inorganic thermal chemical vapor deposition process has been developed for the growth of titanium-silicon-nitride (Ti-Si-N) liners for diffusion barrier applications in ultralarge scale integration copper interconnect schemes. This process employs the thermal reaction of tetraiodotitanium (TiI₄), tetraiodosilane (SiI₄), and ammonia (NH₃) as, respectively, the individual Ti, Si, and N sources. Ti-Si-N films were successfully grown over a broad range of deposition conditions, including wafer temperature, process pressure, and TiI₄, SiI₄, and NH₃ flows ranging, respectively, from 350 to 430°C, 0.1-1 Torr, and 2.5-8.0, 2.5-12.5, and 100-250 seem. Film stoichiometry was tightly tailored through independent control of the Ti, Si, and N source flows. Film properties were characterized by x-ray photoelectron spectroscopy, Rutherford backscattering spectrometry, transmission electron microscopy, scanning electron microscopy, x-ray diffraction, and four-point resistivity probe. Resulting findings indicated that the texture and resistivity of the Ti-Si-N system were dependent on composition. In particular, films with a Ti₃₃Si₁₅N₅₁ stoichiometry exhibited a nanocrystalline TiN phase within an amorphous SiN matrix, highly dense morphology, resistivity of ∼800 μΩ cm for 25 nm thick films, and step coverage of ∼50% in 130 nm wide, 10:1 aspect ratio trenches. Oxygen and iodine contaminant levels were below, respectively, 3 and 1.4 at. % each. Preliminary copper diffusion-barrier studies indicated that barrier failure for 25 nm thick Ti₃₄Si₂₃N₄₃ films did not occur until after annealing for 30 min at 700°C.