This study investigates the material and electrical properties of thin Rh films and nanowires. As-deposited Rh thin films with thicknesses below 30 nm are polycrystalline and show rapid grain growth at approximately 350 degrees C, forming a microstructure dominated by a (111) fiber texture. Compared to Cu, Rh thin films demonstrate a weaker film thickness dependence of the resistivity, leading to a resistivity crossover around 10 nm. The resistivity scaling of these films can be described by the semiclassical Mayadas-Shatzkes model, with grain boundary scattering the limiting factor. Furthermore, Rh nanowires with cross-sectional areas below 70 nm2, fabricated using a metal-spacer etching process, exhibit superior resistivity scaling compared to Ru and Co nanowires, with the potential to significantly outperform state-of-the-art Cu interconnects at line widths around 10 nm. These findings highlight Rh as a promising candidate metal for advanced microelectronic interconnects.

We report the recent results of NiAl and CuAl2 intermetallic compounds for advanced-node interconnect materials in place of Cu. Reported results of Co and Ru are briefly reviewed for comparison. CuAl2 can be a good choice in terms of liner-free and barrier-free interconnections having a low resistivity and a good TDDB and EM reliability.

Intermetallic compounds have been proposed as potential interconnect materials for advanced semiconductor devices. This study reports the interdiffusion reliability and resistivity scaling of three low-resistivity intermetallic compounds (Cu2Mg, CuAl2, and NiAl) formed on thermally grown SiO2. Experimental observations and thermodynamic calculations indicated good interdiffusion reliability with CuAl2 and NiAl but not with Cu2Mg. This was due to slow reaction between Al and SiO2 in conjunction with strong chemical bonds of Cu–Al and Ni–Al. As for resistivity scaling, all three intermetallic compounds showed better resistivity scalability than Cu. Resistivity of the thin films was measured and characteristic parameters were obtained by curve fitting using a classical scattering model. First-principles calculations were carried out to determine the electron mean free path and bulk resistivity in order to explain the resistivity scaling. The results showed the importance of having optimum microstructure features, i.e., low-defect-density surface, interface, and grain boundaries in addition to optimum material properties, i.e., a short mean free path and low bulk resistivity. CuAl2 and NiAl appeared to satisfy the interdiffusion and resistivity conditions and be promising candidates to replace Cu interconnections for future devices.

Materials with low resistivity in small dimensions are urgently desired to replace Cu for highly scaled interconnection in advanced integrated circuits. This study reports the possibility of Cu2Mg intermetallic compound as a Cu alternative by showing adequate adhesion on SiO2, a low resistivity of 25.5 mu Omega cm at 5 nm film thickness and good trench-filling capability in trench width of 38 or 23 nm by sputtering reflow. However, annealing at 400 degrees C for 30 min led to the dielectric current leakage associated with the formation of a thick MgO layer. Furthermore, Mg composition inside the trenches was less than the stoichiometric Cu2Mg composition. Theoretical calculation of surface diffusion process revealed that the adatom hopping of Mg atoms was slower than that of Cu atoms, which resulted in the Mg-poor composition inside the trenches.

Cu 2 Mg intermetallic compound was selected as a candidate material for liner-barrier free interconnects for advanced LSI interconnects. The blanket films of Cu 2 Mg showed an excellent resistivity scaling with resistivity value of only 25 μΩcm at a film thickness of 5 nm. However, a thick MgO layer was formed within the underlying SiO 2 layer by interface reaction between Cu 2 Mg and SiO 2 . Progressive growth of MgO made it unfavorable for Cu 2 Mg to be used as liner-barrier free interconnects.

New interconnect materials that have a low line resistivity are required to address issues associated with the increased resistivity due to the aggressive downscaling of future semiconductor devices. In this work, CuAl2 thin films are investigated as a potential material for liner- and barrier-free interconnect applications. The results show that CuAl2 blanket films adhere well to and do not undergo interdiffusion with SiO2, as well as having a favorable size effect of resistivity. Furthermore, the filling of CuAl2 in narrow low-k trenches is investigated, and an excellent gap-filling performance is registered. These features suggest that CuAl2 is a promising alternative to Cu that does not require any additional liner or barrier layers for feature sizes less than 10 nm.

This study reports the time-dependent-dielectric-breakdown (TDDB) reliability of NiAl on SiO2 without any barrier layer. NiAl was indicated to exhibit superior TDDB reliability in comparison to Cu/TaN in the time-to-failure (4200 s versus 240 s, at 4 MV/cm at 200 degrees C) and in the breakdown activation energy under 4 MV/cm (1.17 eV versus 0.87 eV). Moreover, NiAl was found to form an atomically thin and self-limiting Al oxide layer at the NiAl/SiO2 interface, and this Al oxide layer, together with the large cohesive energy of NiAl, was considered to be possible origin for the excellent reliability. The results demonstrate a great potential of NiAl as a liner-and barrier-free interconnect material.

Because of aggressive downscaling of the dimensions of future semiconductor devices, they will suffer from increased line resistivity and resistance-capacitance delay. In this work, NiAl thin films are investigated as a potential liner- and barrier-free interconnect material. The results show that NiAl has strong adhesion, does not undergo interdiffusion with SiO2, and has a favorable resistivity size effect. These features suggest that NiAl is a good candidate for replacing Cu as a liner- and barrier-free interconnect for linewidths below 7 nm.

Acid-stable, non-noble catalysts are promising for hydrogen evolution reaction (HER); however, they get easily damaged when used in acidic electrolytes, thus reducing the HER lifetimes. Moreover, completely blocking catalysts from acidic electrolytes degrades HER performance. To achieve a balance between the HER lifetime and performance, we vary the number of N-doped graphene layers (1-2, 2-3, and 3-5 layers) encapsulating NiMo nanoparticles as efficient HER catalysts and obtain the optimal number of protective layers. Our data show that 3-5 graphene layers achieved the best balance, with a stable current density of 100 mA cm(-2) for 25 h in 0.5 M H2SO4. Density functional theory calculations are performed to show the effect of encapsulating graphene layer number on the catalytic activity and protection of non-noble NiMo in acidic electrolytes.

Three-dimensional bicontinuous open (3DBO) nanoporosity has been recognized as an important nanoarchitecture for catalysis, sensing, and energy storage. Dealloying, i.e., selectively removing a component from an alloy, is an efficient way to fabricate nanoporous materials. However, current electrochemical and liquid-metal dealloying methods can only be applied to a limited number of alloys and usually require an etching process with chemical waste. Here, we report a green and universal approach, vapor-phase dealloying, to fabricate nanoporous materials by utilizing the vapor pressure difference between constituent elements in an alloy to selectively remove a component with a high partial vapor pressure for 3DBO nanoporosity. We demonstrate that extensive elements, regardless of chemical activity, can be fabricated as nanoporous materials with tunable pore sizes. Importantly, the evaporated components can be fully recovered. This environmentally friendly dealloying method paves a way to fabricate 3DBO nanoporous materials for a wide range of structural and functional applications.

The development of noble-metal-free hydrogen evolution reaction (HER) materials for electrochemical water splitting is the key to achieving low-cost and efficient electrocatalysis that drives electrochemical hydrogen evolution. However, the electrocatalytic activities of most non-noble metals decrease in acidic electrolytes. Here, we have fabricated non-noble-metal electrodes using a bicontinuous and open porous NiMo alloy covered by nitrogen-doped (N-doped) graphene with nanometer-sized holes. This noble-metal-free HER catalyst exhibits performance almost identical with that of a Pt/C electrode, while its original catalytic activity is preserved even in acidic electrolytes. Density functional theory calculations indicate that the interfacial fringes between the nanoholes and NiMo surface induce charge transfer and promote hydrogen adsorption and desorption. The nanometer-sized holes simultaneously provide minimal surface area for chemical reactions, while delaying NiMo dissolution in excessive amounts of acidic electrolyte. Our method for the fabrication of the NiMo alloy provides a route to a promising class of electrochemical hydrogen-producing electrodes.

Heavy chemical doping and high electrical conductivity are two key factors for metal-free graphene electrocatalysts to realize superior catalytic performance toward hydrogen evolution. However, heavy chemical doping usually leads to the reduction of electrical conductivity because the catalytically active dopants give rise to additional electron scattering and hence increased electrical resistance. A hierarchical nanoporous graphene, which is comprised of heavily chemical doped domains and a highly conductive pure graphene substrate, is reported. The hierarchical nanoporous graphene can host a remarkably high concentration of N and S dopants up to 9.0 at% without sacrificing the excellent electrical conductivity of graphene. The combination of heavy chemical doping and high conductivity results in high catalytic activity toward electrochemical hydrogen production. This study has an important implication in developing multi-functional electrocatalysts by 3D nanoarchitecture design.

The interplay between chemical dopants and topological defects plays a crucial role in electrocatalysis of doped graphene. By systematically tuning the curvatures, thereby the density of topological defects, of 3D nanoporous graphene, the intrinsic correlation of topological defects with chemical doping contents and dopant configurations is revealed, shining lights into the structural and chemical origins of HER activities of graphene.