Electron scattering at surfaces and grain boundaries in Cu thin films and wires

Abstract

The electron scattering at surfaces, interfaces, and grain boundaries is investigated using polycrystalline and single-crystal Cu thin films and nanowires. The experimental data is described by a Fuchs-Sondheimer (FS) and Mayadas-Shatzkes (MS) model that is extended to account for the large variation in the specific resistivity of different grain boundaries as well as in situ anneal and a subsequent etch to match the thickness of the SG samples. Nanowires are fabricated from the SG and LG thin films using a subtractive patterning process, yielding wire widths of 75-350 nm. Single-crystal and LG layers exhibit a 18-22% and 10-15% lower resistivity than SG layers, respectively. The resistivity decrease from SG to LG Cu nanowires is 7-9%. The thickness and grain size dependence of the resistivity of polycrystalline and singlecrystal Cu layers is well described by an exact version of the existing FS+MS model, but is distinct from the commonly used approximation which introduces an error that increases with decreasing layer thickness from 6.5% for d = 50 nm to 17% for d = 20 nm. The case of nanowires requires the FS+MS model to be extended to account for variation in the grain boundary reflection coefficient R, which effectively increases the overall resistivity by, for example, 16% for 50×45 nm 2 wires. The overall data from single and polycrystalline Cu layers and wires yields R = 0.25±0.05, and p = 0 at Cu-air and Cu-Ta interfaces.2

Experimental study of electron-phonon coupling and electron internal thermalization in epitaxially grown ultrathin copper films

“…The effects of electron scattering in a confined geometry have been studied extensively in thin copper films [5][6][7][8][9][10] and nanoscale copper wires [2,[11][12][13][14][15]. When the sample size is reduced to the nanoscale level, the increase of electrical resistivity has been mostly explained by the increase in surface and grain boundary scattering [14,16]. It is less clear if the electron-phonon coupling strength changes when the sample size is reduced.…”

Metallic Glass Nano-composite Thin Films for High-performance Functional Applications

“…The increased volume fraction of nano-crystallites for the 100-nm and 200-nm films likely results in greater surface and grain boundary scattering of electrons resulting in lower conductivity. [32][33][34][35] These scattering events manifest as broadening of Ag and Cu d-band edge with lowering of their peak intensity.…”

Electron transport properties of sub-3-nm diameter copper nanowires

“…Hence, in these nanostructures, electrical resistivity can be expected to be dominated by surface scattering. While standard complementary metal-oxide semiconductor (CMOS) technologies employ Ta-based materials as barrier layers to prevent Cu diffusion, deposited Ta has been shown to cause diffusive scattering at the surface of thin Cu films [16]. As scaling continues, the relative contribution of surface scattering to total scattering increases dramatically and along with the barrier thickness means that Ta-based barrier layers may well become unsuitable for efficient interconnect design.…”

“…In a series of studies [14][15][16], Chawla and co-workers have investigated the scattering at the surfaces of Cu thin films. They report that scattering at a Cu-vacuum surface is partially specular, whereas after tantalum deposition the surface scattering becomes diffuse [14,16]. The effect of oxygen has also been reported, with diffuse scattering again reported after oxidation [15].…”