Intrinsic Properties and Barrier Behaviors of Thin Films of Sputter-Deposited Single-Layered and Alternately Layered Tantalum Nitrides (Ta[sub 2]N/TaN)

This work employs X-ray diffraction, X-ray reflectivity, and transmission electron microscopy, along with electrical (sheet resistance and resistivity) and bending-beam stress analyses, to characterize the intrinsic properties and barrier behavior of 40 nm thick thin films of sputter-deposited single-layered Ta 2 N , single-layered TaN, and alternately layered Ta 2 N / TaN having various period thicknesses (λ) from 4 to 40 nm. The thermal stability of each of these barriers interposed between silicon and copper at a high temperature regime (500-900°C) is closely related to variations of intrinsic properties of the barriers, particularly microstructure and residual stress (σ). Failure of the barriers is explained in terms of a previously reported mass transport mechanism, which suggests that the free short-diffusion paths (grain boundaries) created by anneal-induced crystallization/grain growth in the single-layered Ta 2 N and TaN barriers (σ = 3-5 GPa) are a key factor in deteriorating the diffusion barriers. Conversely, an adequately layered Ta 2 N / TaN barrier with λ down to approximately 5 nm is nearly free of residual stress and can maintain a very stable quasi-amorphous microstructure against annealing. Therefore, this quasi-superlattice novel design has the capability to further improve thermal stability and reliability of tantalum nitride diffusion barriers for copper metallization.