IBM Research at Albany Nanotech has recently published work with ATK investigating four novel metal nanowires as back-end-of-line interconnects.
The paper [1] demonstrates potential superior performance to the current Cu based nanowires as the future brings continued down-scaling of modern transistor technology.
Three properties required for the good performance of interconnects are:
1) High structural integrity and resistance to electromigration.
2) Low electrical resistivity due to surface scattering.
3) Low electrical resistivity due to grain boundary scattering.
ATK was used to evaluate these three properties of Pt, Rh, Ir, Pd, and Cu nanowires (0.5 nm - 3 nm wide):
1) The cohesive energy was calculated with the ATK-DFT cohesive energy calculation tool.
This predicts bond strengths and how robust different sized nanowires will be when used as interconnects.
2) The conductance was calculated with the ATK-DFT+NEGF electron transport tool, with different sizes and orientations of the nanowires.
This predicts the electrical resistivity due to surface scattering for each orientation.
3) The conductance was calculated with the ATK-DFT+NEGF electron transport tool, with different grain boundaries in the scattering region. This predicts the electrical resistivity (relative to the bulk resistivity) for different grain sizes. Specific resistivities for Cu grain boundaries are in a good agreement with experimental and computational work.
Nanowires with and without grain boundaries were constructed and optimized using the VNL user interface for the crystal builder.
Schematic illustration of the transistor-interconnect technology for which properties of Pt, Rh, Ir and Pd nanowires were calculated using ATK. Cross section of nanowire oriented along [110] is shown together with cohesive energy as a function of nanowire width (1), conductance/area for various metals (2) and relative resistivity as a function of average grain size (3).
(1) and (2) properties of Pt, Rh and Ir nanowires are superior to Cu. However, Cu outperforms the other metals in (3).
References
[1] N. A. Lanzillo, "Ab initio evaluation of electron transport properties of Pt, Rh, Ir, and Pd nanowires for advanced interconnect
applications", J. Appl. Phys. 121, 175104 (2017).