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Copper (Cu) interconnects are an increasingly important bottleneck in integrated circuits due to energy consumption and latency caused by the notable increase in Cu resistivity as dimensions decrease, primarily due to electron scattering at surfaces. Herein, the potential of a directional conductor, PtCoO₂, which has a low bulk resistivity and a distinctive anisotropic structure that mitigates electron surface scattering is showcased. Thin films of PtCoO₂of various thicknesses are synthesized by molecular beam epitaxy (MBE) coupled with a postdeposition annealing process and the superior quality of PtCoO₂films is demonstrated by multiple characterization techniques. The thickness‐dependent resistivity curve illustrates that PtCoO₂significantly outperforms effective Cu (Cu with TaN barriers) and Ru in resistivity below 20.0 nm with a more than 6x reduction compared to effective Cu below 6.0 nm, having a value of only 6.32 μΩ cm at 3.3 nm. It is determined that grain boundary scattering can still be improved for even lower resistivities in this material system through a combination of experiments and theoretical simulations. PtCoO₂is therefore a highly promising alternative material for future interconnect technologies promising lower resistivities, better stability, and significant improvements in energy efficiency and latency for advanced integrated circuits. 

Electron transport measurements on 60-nm-thick multilayers containing N = 2–58 individual Ru and Co layers are employed to quantify the specific resistance of Ru/Co interfaces. Sputter deposition on Al2O3(0001) at Ts = 400 °C leads to a 0001 preferred orientation with x-ray diffraction (XRD) Ru and Co 0002 peaks that shift closer to each other with increasing N, suggesting interfacial intermixing. The intermixing is quantified by x-ray reflectivity (XRR) and confirmed by an XRD Ru/Co alloy peak that develops during in situ synchrotron annealing as well as for deposition at a higher Ts = 600 °C. The room-temperature resistivity increases from 15.0 to 47.5 μΩ cm with decreasing superlattice period Λ = 60–2 nm. This is attributed to increasing electron scattering at the intermixed metal interfaces. The transport data are well described by a parallel conductor model that treats metal layers and the intermixed alloy as parallel resistors, where the resistivity of the intermixed alloy of 60.4 μΩ cm is determined from a co-deposited Ru/Co sample. Data fitting provides values for the effective thickness of the intermixed interface of 16.8 nm, in good agreement with the XRR value, yielding a Ru/Co contact resistance of 8.5 × 10−15 Ω m2 for interfaces deposited at 400 °C. The overall results show that the Ru/Co contact resistance is dominated by a high-resistivity interfacial alloy and, therefore, is a strong function of the deposition process, particularly the processing temperature. 

Epitaxial W–Mo multilayers are employed as a model system to demonstrate how resistivity measurements parallel to metal–metal interfaces can be used to quantify the specific interface resistance without sub-10-nm patterning that would be required for direct transport measurements across the interface. 50-nm-thick epitaxial multilayer stacks containing 2–60 individual W(001) and Mo(001) layers are deposited on MgO(001) substrates and their resistivity ρ measured as a function of superlattice period Λ at 293 and 77 K. The measured room temperature ρ increases from 7.10 to 8.62 μΩ cm with decreasing Λ = 50–1.7 nm, which is attributed to the increasing electron-interface scattering. The semiclassical Fuchs–Sondheimer model for surface scattering dramatically overestimates the resistivity, which is attributed to coherent electron transmission across multiple interfaces. A new Boltzmann transport model treats each interface as a boundary condition where electrons either scatter diffusely or traverse without momentum loss with a probability T for the first encountered interface and with 100% transmission at subsequent interfaces until they are relaxed by a bulk scattering event. This model has a single unknown parameter T, which becomes the fitting parameter for experimental data analysis, yielding a temperature-independent T = 0.8 ± 0.1 and a corresponding contact resistance at the W(001)–Mo(001) interface of 2.6 × 10−16 Ω m2. 

CuTi layers are co-sputter deposited on 20-nm-SiO2/Si(001) wafers at 350 ℃ to quantify their stability in direct contact with a dielectric and to explore the potential of CuTi as barrier- and liner-free interconnect metal. X-ray diffraction pole figures indicate a preferred 001 out-of-plane crystalline orientation and Rutherford backscattering confirms a stoichiometric composition. Vacuum annealing tests at 450 ℃ of CuTi layers indicate considerably higher thermal stability than for pure Cu layers, including negligible dewetting observed by scanning electron microscopy and negligible intermixing with the oxide substrate quantified by photoelectron spectroscopy. Four-point bend tests show a 25% higher interfacial toughness for CuTi/SiO2 than Cu/SiO2 interfaces. CuTi/SiO2 samples also exhibit a 300-times longer failure time than Cu/SiO2 during time-dependent dielectric breakdown tests using an externally applied 3 MV/cm electric field. The higher stability of CuTi in comparison to Cu is attributed to a higher cohesive energy in combination with an atomically thin self-limiting Ti oxide layer at the CuTi/SiO2 interface. 

The electron reflection probability r at symmetric twin boundaries Σ3, Σ5, Σ9, and Σ11 is predicted from first principles for the eight most conductive face-centered cubic (fcc) metals. r increases with decreasing interplanar distance of atomic planes parallel to the boundary. This provides the basis for an extrapolation scheme to estimate the reflection probability r r at random grain boundaries, which is relatively small, r r = 0.28–0.39, for Cu, Ag, and Au due to their nearly spherical Fermi surfaces, but approximately two times higher for Al, Ca, Ni, Rh, and Ir with a predicted r r = 0.61–0.72. The metal resistivity in the limit of small randomly oriented grains with fixed average size is expected to be proportional to the materials benchmark quantity ρ o λ × r r /(1 − r r ), where ρ o and λ are the bulk resistivity and bulk electron mean free path, respectively. Cu has the lowest value for this quantity, indicating that all other fcc metals have a higher resistivity in the limit of small randomly oriented grains. Thus, the conductivity benefit of replacement metals for narrow Cu interconnect lines can only be realized if the grains are larger than the linewidth or exhibit symmetric orientation relationships where r < r r .