Paper TF-ThM7
Surface Morphology of Epitaxial Cu Layers: The Effect of Roughness on Electron Scattering

Thursday, October 18, 2007, 10:00 am, Room 613/614

Single crystal Cu layers, 12 to 600 nm thick, were grown on MgO(001) by ultra-high vacuum magnetron sputtering. X-ray diffraction θ-2θ, ω-rocking curve, and pole figure scans show that layers grown at temperatures T_s ≤ 100 °C exhibit a cube-on-cube epitaxy, while T_s ≥ 200 °C results in polycrystalline copper layers. The surfaces of the single crystal layers exhibit regular mound structures, as observed by in-situ scanning tunneling microscopy. The mounds grow in width with increasing layer thickness t, from 21 nm for t = 24 nm to 33 nm with t = 119 nm. In-situ vacuum annealing at 200 and 300 °C leads to a successive smoothening of the surfaces for all thickness values. For example, for t = 24 nm, the RMS roughness is 1.3 nm for the as-deposited layer and decreases to 0.7 nm after the post-deposition anneal. The measured resistivity increases for decreasing layer thickness, from 1.70 μΩ-cm for t = 604 nm to 2.91μΩ-cm for t = 24 nm. This increase is consistent with the Fuchs-Sondheimer model, indicating completely diffuse surface scattering. The diffuse surface scattering is attributed to atomic level roughness, as quantified by the average width of atomically smooth surface terraces, which increases from 0.5 nm for the as-deposited layer to 1.5 nm for the film annealed at 300 °C. Therefore, even the smoothest layers exhibit terraces that are only 8 atoms wide, which is insufficient to result in specular electron surface scattering.