Intrinsic properties and barrier behaviors of thin films of sputter-deposited single-layered and alternately layered tantalum nitrides (Ta2N/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 Ta2N, single-layered TaN, and alternately layered Ta2N/TaN having various period thicknesses (lambda) 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 degreesC) is closely related to variations of intrinsic proper-ties of the barriers, particularly microstructure and residual stress (sigma). 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 Ta2N and TaN barriers (sigma = 3-5 GPa) are a key factor in deteriorating the diffusion barriers. Conversely, air adequately layered Ta2N/TaN barrier with lambda 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, (C) 2001 The Electrochemical Society. [DOI: 10.1149/1.1383073] All rights reserved.