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Evaluation of single-and multilayered amorphous tantalum nitride thin films as diffusion barriers in copper metallization J.

This work employs X-ray diffraction, X-ray reflectivity, and transmission electron microscopy, along with electrical ͑sheet resistance and resistivity͒ 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 ͑͒ 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°C͒ is closely related to variations of intrinsic properties of the barriers, particularly microstructure and residual stress ͑͒. Failure of the barriers is explained in terms of a previously reported mass transport mechanism, which suggests that the free short-diffusion paths ͑grain boundaries͒ created by anneal-induced crystallization/grain growth in the single-layered Ta 2 N and TaN barriers ͑ ϭ 3-5 GPa͒ are a key factor in deteriorating the diffusion barriers. Conversely, an adequately layered Ta 2 N/TaN barrier with 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.

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