Surface and grain-boundary scattering in nanometric Cu films

Abstract

We report a quantitative analysis of both surface and grain-boundary scattering in Cu thin films with independent variation in film thickness ͑27 to 158 nm͒ and grain size ͑35 to 425 nm͒ in samples prepared by subambient temperature film deposition followed by annealing. Film resistivities of carefully characterized samples were measured at both room temperature and at 4.2 K and were compared with physical models that include the effects of surface and grain-boundary scattering. Grain-boundary scattering is found to provide the strongest contribution to the resistivity increase. However, a weaker, but significant, role is observed for surface scattering. We find that the data are best fit when the Mayadas and Shatzkes' model of grain-boundary scattering and the Fuchs and Sondheimer's model of surface scattering resistivity contributions are combined using Matthiessen's rule ͑simple addition of resistivities͒. This finding implies that grain-boundary scattering preserves the component of electron momentum parallel to the grain-boundary plane. Using Matthiessen's rule, we find our data are well described by a grain-boundary reflection coefficient of 0.43 and a surface specularity coefficient of 0.52. This analysis finds a significantly lower contribution from surface scattering than has been reported in previous works and we attribute this difference to the careful quantitative microstructural characterization performed on our samples. The effects of surface roughness, impurities, voids, and interactions between surface and grain-boundary scattering are also examined and their importance is evaluated.

Universal scaling of the critical temperature for thin films near the superconducting-to-insulating transition

“…We also examined our own new experimental data on NbN thin films. In these data, relating dT c to R s provided fits with reduced scatter relative to fits suggested by previous models [7][8][9][10][30][31][32]. Finally, we supply two possible explanations of the observed universal behavior.…”

“…Figures 1(a) and 1(b) show the dependence of T c on thickness and on sheet resistance for our NbN films, allowing a comparison of the data with the existing models [7][8][9][10][30][31][32]. Although a general trend can be seen in both T c (d) and T c (R s ), Chemical treatment of the substrate prior to deposition is suspected of influencing the properties of the red solid points here and in Fig.…”

“…Theoretically, the relationship ρ(d) is usually discussed in terms of derivatives of Fuchs's theory [30], sometimes combined with Matthiessen's rule [31]. However, surprisingly, to date, the existing theories encounter difficulties in fitting the experimental data, which are often scattered when plotted on a ρ(d) graph [32]. In addition to challenging our understanding of metallic thin films, such scatter prevents a smooth quantitatively valuable transition between descriptions of T c (R s ) and T c (d) in the case of superconductors.…”

On twin density and resistivity of nanometric Cu thin films

“…Prior work by Sun et al [2][3][4] on SiO 2 and Ta/SiO 2 -encapsulated nanometric Cu films showed grain-boundary scattering to be the dominant mechanism contributing to the resistivity increase related to the classical size effect. These studies also showed a weaker, but still significant, contribution from surface scattering.…”

Direct-Liquid-Evaporation Chemical Vapor Deposition of Nanocrystalline Cobalt Metal for Nanoscale Copper Interconnect Encapsulation

“…[10][11][12] As a result, by adding several nanometers of a low conductivity tantalum nitride barrier layer (~10 6 S/m) onto Cu (5.96 × 10 7 S/m), the effective width of a Cu wire would be decreased by 10 -20 %, thus drastically decreasing the overall conductivity of the nanoscale interconnects. [13][14] Therefore, a high-conductivity metallic material with Cu stabilization functionalities is needed for furtherdown-sized microelectronic interconnects.…”