Large discrete resistance jump at grain boundary in copper nanowire
X.-G. Zhang,1 D. M. Nicholson,1 B. M. Evans,1 N. S. Kulkarni,2
B. Radhakrishnan,1 E. A. Kenrik,1 and A-P. Li1
1- Oak Ridge National Laboratory, Oak Ridge, TN
2-University of Tennessee, Knoxville, TN
Copper is the current interconnect metal of choice in integrated circuits. As interconnect dimensions decrease, the resistivity of copper increases dramatically because of electron scattering from surfaces, impurities, and grain boundaries (GBs), and thus threatens to stymie continued device scaling. Lacking direct measurements of individual scattering sources, understanding of the relative importance of these scattering mechanisms has largely relied on semiempirical modeling. In this paper, we report on a first-ever attempt to measure and calculate individual GB resistances in copper nanowires with one-to-one correspondence to the GB structure. By directly measuring both intra- and inter-grain resistance with a unique four-probe scanning tunneling microscope, we observed surprisingly large resistance jumps across high-angle random GBs, while the resistance of coincidence boundaries are negligibly small. Strikingly, the high resistance for random boundaries is found to be an intrinsic result arising from the scaling of the electron mean free path with the size of the relaxation region near the GBs.
Left Figure: Microstructures of copper nanowires. (a), The inverse pole figure of EBSD map showing the crystallographic orientations of grains in the copper sample. (b), SEM image showing four-probe STM contacted onto the same copper nanowire. (c), A schematic illustrating the sample structure and the resistance measurement procedure.
Right Figure: resistance jumps near random grain boundaries.
This paper has shown for the first time that the GB scattering effect can differ by orders of magnitude depending on the level of structural symmetry. The results thus provide compelling evidence on the importance of GB scattering process, particularly at random GBs, and also suggests a path to suppressing the GB scattering effect in polycrystalline nanowires through the conversion of random GBs into coincidence GBs. It has provided a long-sought breakthrough in the debate over GB conductivity. Moreover, the experimental and theoretical approaches applied to GBs can be duplicated in other areas where currents have to flow across domain boundaries and other interfaces to activate or sense at the nanoscale including in magnetic structures, carbon based nanotechnology, and oxide heterojunctions. The result will thus be of great interest to nanoscience and nanotechnology as a whole.
This work was published in Nano Letters, 2010, 10 (8), pp 3096–3100. This research was sponsored by the Laboratory Directed Research and Development Program of Oak Ridge National Laboratory, managed by UT-Battelle, LLC, for the U.S. Department of Energy (THK, BME, NSK, BR) and the Scientific User Facilities Division (XGZ, EAK, APL) and the Division of Materials Sciences and Engineering (DMN), U.S. Department of Energy.
for highlight: “Large discrete resistance jump at grain boundary in copper nanowire”, Nano Letters, 2010, 10 (8), pp 3096–3100 DOI: 10.1021/nl101734h.