Atomic layer deposition (ALD) is an advanced technology that can be used to deposit extremely thin and conformal films of iridium (Ir). However, ALD techniques for Ir coating are not well-developed. In particular, new Ir precursors with high reactivity at a suitable low temperature are essentially required. In this study, we report a novel ALD precursor with improved reactivity by introducing a cyclopropenyl ligand. Tricarbonyl (1,2,3-η)-1,2,3-tri(tert-butyl)-cyclopropenyl iridium (C 18 H 27 IrO 3 or TICP) is used as an ALD precursor with molecular O 2 as a reactant. Ir films are grown by ALD on a Si substrate at deposition temperatures ranging from 200 to 325 °C, and an ALD window of 250−275 °C and self-limiting growth at a rate of 0.52 Å cycle −1 at 250 °C are observed. The negligible O impurity content (<2 at. %) and low resistivity (13 μΩ cm) indicate that pure metallic Ir films are formed. The differential delay of nucleation depending on the substrate surface is explained in terms of the dominant surface functional group, indicating possible application of the current ALD process toward area-selective deposition of Ir. Density functional theory calculations show that the adsorption of the Ir precursor is feasible on Si and Ru but is unfavorable on hydroxyl-terminated SiO 2 . Ru is adopted as the seed layer for conformal deposition on a SiO 2 trench, and a step coverage of ∼100% is obtained. Finally, an Ir thin film grown on a threedimensional titanium substrate shows overpotentials (at 10 mA cm −2 ) of ∼65 mV for the hydrogen evolution reaction and ∼336 mV for the oxygen evolution reaction in an acid electrolyte, which suggest its potential application as a water-splitting catalyst.
Atomic layer deposition (ALD) is a suitable technology for conformally depositing thin films on nanometer‐scale 3D structures. RuO2 is a promising diffusion barrier for Ru interconnects owing to its compatibility with Ru ALD and its remarkable diffusion barrier properties. Herein, a RuO2 diffusion barrier using an ALD process is developed. The highly reactive Ru precursor [tricarbonyl(trimethylenemethane)ruthenium] and improved O2 supply enable RuO2 deposition. The optimal process conditions [pulsing time ratio (tO2/tRu): 10, process pressure: 1 Torr, temperature: 180 °C] are established for the RuO2 growth. Growth parameters, such as the growth rate (0.56 Å cycle–1), nucleation delay (incubation period: 6 cycles), and conformality (step coverage: 100%), are also confirmed on the SiO2 substrate. The structural and electrical properties of the Ru/RuO2/Si multilayer are investigated to explore the diffusion barrier performance of the ALD‐RuO2 film. The formation of Ru silicide does not occur without the conductivity degradation of the Ru/RuO2/Si multilayer with an increase in the annealing temperature up to 850 °C, thus demonstrating that interdiffusion of Ru and Si is completely suppressed by a thin (5 nm) ALD‐RuO2 film. Consequently, the practical growth behavior and diffusion barrier performance of RuO2 can serve as a potential diffusion barrier for Ru interconnects.
The recent introduction of alkali metal halide catalysts for chemical vapor deposition (CVD) of transition metal dichalcogenides (TMDs) has enabled remarkable two‐dimensional (2D) growth. However, the process development and growth mechanism require further exploration to enhance the effects of salts and understand the principles. Herein, simultaneous predeposition of a metal source (MoO3) and salt (NaCl) by thermal evaporation is adopted. As a result, remarkable growth behaviors such as promoted 2D growth, easy patterning, and potential diversity of target materials can be achieved. Step‐by‐step spectroscopy combined with morphological analyses reveals a reaction path for MoS2 growth in which NaCl reacts separately with S and MoO3 to form Na2SO4 and Na2Mo2O7 intermediates, respectively. These intermediates provide a favorable environment for 2D growth, including an enhanced source supply and liquid medium. Consequently, large grains of monolayer MoS2 are formed by self‐assembly, indicating the merging of small equilateral triangular grains on the liquid intermediates. This study is expected to serve as an ideal reference for understanding the principles of salt catalysis and evolution of CVD in the preparation of 2D TMDs.
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