Ru Atomic Layer Deposition Research Articles

Growth of Atomic Layer Deposited Ruthenium and Its Optical Properties at Short Wavelengths Using Ru(EtCp)2 and Oxygen

High-density ruthenium (Ru) thin films were deposited using Ru(EtCp)2 (bis(ethylcyclopentadienyl)ruthenium) and oxygen by thermal atomic layer deposition (ALD) and compared to magnetron sputtered (MS) Ru coatings. The ALD Ru film growth and surface roughness show a significant temperature dependence. At temperatures below 200 °C, no deposition was observed on silicon and fused silica substrates. With increasing deposition temperature, the nucleation of Ru starts and leads eventually to fully closed, polycrystalline coatings. The formation of blisters starts at temperatures above 275 °C because of poor adhesion properties, which results in a high surface roughness. The optimum deposition temperature is 250 °C in our tool and leads to rather smooth film surfaces, with roughness values of approximately 3 nm. The ALD Ru thin films have similar morphology compared with MS coatings, e.g., hexagonal polycrystalline structure and high density. Discrepancies of the optical properties can be explained by the higher roughness of ALD films compared to MS coatings. To use ALD Ru for optical applications at short wavelengths (λ = 2–50 nm), further improvement of their film quality is required.

Area-Selective Atomic Layer Deposition Using Si Precursors as Inhibitors

Short-chain aminosilanes, namely, bis(N,N-dimethylamino)dimethylsilane (DMADMS) and (N,N-dimethylamino)trimethylsilane (DMATMS), have been used as Si precursors for atomic layer deposition (ALD) of SiO2. In this work, the DMADMS and DMATMS Si precursors are utilized as inhibitors for area-selective ALD (AS-ALD). The inhibitors selectively adsorb on a SiO2 surface but not on H–Si, so that SiO2 becomes selectively deactivated toward subsequent ALD. The deactivation of the SiO2 surface by the inhibitors was investigated using various experimental and theoretical methods, including surface potential measurements, spectroscopic ellipsometry, and X-ray photoelectron spectroscopy. Better inhibition was observed for ALD of Ru and Pt than for ALD of Al2O3 and HfO2. Through quantum mechanical and stochastic simulations, the difference in the blocking ability for noble metal and metal oxide ALD by the aminosilane inhibitors could be attributed to the inherently partial surface coverage by the inhibitors at their saturation and the reactivity of the subsequent ALD precursors. As silane inhibitors can be easily integrated with vacuum-based processes to facilitate high volume manufacturing of upcoming electronic devices, the current study provides a potential approach for the utilization of AS-ALD in pattern fabrication inside 3D nanostructures.

Inherent Area-Selective Growth and Nucleation Enhancement during Ru ALD Using the RuO4-Precursor and H2-Gas

Ruthenium is a candidate to replace copper in future sub-10 nm interconnects. At these dimensions the resistivity of Ru lines is expected to be lower compared to Cu due to the lower sensitivity to size effects.1 In addition, it is likely that Ru interconnects won’t require a diffusion barrier, and will show a better electromigration performance.2 At feature sizes below 10 nm it will be difficult to align subsequent lithography steps, and the conformality of the deposition method is increasingly important, such that area selective atomic layer deposition (ALD) of ruthenium is of high interest.3 We first report inherent area selective ALD of Ru on H-terminated Si (Si-H) versus SiO2, using the thermal RuO4 (ToRuSTM)/ H2-gas ALD process.4 In situ spectroscopic ellipsometry (SE) on blanket substrates shows that Ru growth initiation occurs from the first cycle on Si-H, while on SiO2 the growth is delayed, resulting in a substrate selectivity window of ~ 70 cycles. Area selective Ru ALD was evaluated using a patterned substrate of 1-10 µm wide Si-H lines separated by 10 µm wide SiO2 regions, and exposing it to 20 cycles of the RuO4 / H2-gas ALD process. Ex situ scanning electron microscopy (SEM) and cross section high resolution transmission electron microscopy (HRTEM) measurements show that a 4.5 nm Ru film could be deposited on the Si-H, with no Ru detected on the SiO2. In vacuo X-ray photoelectron spectroscopy (XPS) experiments showed that exposure of Si-H to a single RuO4 pulse leads to the oxidation of the Si surface, together with the deposition of RuO2. On SiO2 however, the surface is already oxidized, and in vacuo XPS shows that for the same exposure to RuO4 no Ru is deposited on the surface. Therefore, we propose that the mechanism behind the inherent substrate selectivity is the oxidation of the Si-H surface by RuO4. Secondly, we report for a methodology to enhance the nucleation of the RuO4 / H2-gas process on oxide substrates. In vacuo XPS and in situ SE experiments show that a single exposure of SiO2 to trimethylaluminum (TMA) makes the surface reactive towards RuO4, which allows for Ru growth initiation from the first cycle. We propose that this is due to the combustion of surface CH3-groups by RuO4. As TMA is known to be reactive towards many oxide substrates, this methodology presents a way to achieve Ru metallization of virtually any surface. [1] S. Dutta et al. IEEE Elec. Dev. Lett. 2017, 38, 949. [2] O. V. Pedreira et al . 2017 IEEE IRPS , Monterey, CA, 6B-2.1. [3] P. C. Lemaire et al. J. Chem. Phys. 2017, 146, 052811. [4] M. M. Minjauw et al. J. Mater. Chem. C. 2015, 3, 132.

Properties of Annealed ALD Ru from Ru(DMBD)(CO)3 and Oxygen

Ruthenium metal has a low bulk resistivity (7.1 μΩ cm), a high work function (4.7 eV), and a low solid solubility with strong adhesion to Cu, and is etchable, making Ru an attractive barrier metal or seed layer for Cu electroplating.1 For these applications, conformal deposition on the high-aspect ratio structures encountered in the back end of line (BEOL) of ultra largescale integration (ULSI) circuits is required. Atomic layer deposition (ALD), based on purge-separated dosing of precursors and self-saturating surface reactions, allows for atomic scale control and inherent high conformality. Because of these advantages, ALD processes for Ru are strongly desired. Although a number of ALD processes for Ru have been reported, currently the most widely reported Ru ALD precursor, Ru(EtCp)2, as well as other non-zero oxidation state precursors show long nucleation delays (~ 200 ALD cycles) prior to film growth. As nucleation delays can result in island growth and increased roughness and Ru films used in ULSI applications are generally only a few to tens of nanometers thick, nucleation delay is a critical growth parameter. More recent work has shown that zero oxidation state Ru precursors can significantly reduce nucleation delays for O2-based thermal ALD processes. However, the resistivities of these films are generally 18-40 µ-ohm cm, well above the bulk value. Very recently, a zero oxidation state ALD Ru process based on η4-2,3- dimethylbutadiene ruthenium tricarbonyl [Ru(DMBD)(CO)3] and O2, showed zero nucleation delay, a surface roughness of 0.6 nm RMS, and a resistivity of 14 µΩ-cm.2 Although the resistivity of films deposited using this Ru(DMBD)(CO)3 / O2 process is among the lowest values reported for ALD Ru, it still larger than the resistivity of pure ruthenium. It was speculated that residual oxygen resident in the film was the cause of the higher than bulk resistivity. In this work, we investigate the impact of annealing on the structure and electronic properties of ALD Ru. ALD Ru was deposited on either Si or Si/SiO2 substrates in a Picosun R-200 SunALE reactor at 260˚C using pure separated pulses of Ru(DMBD)(CO)3 & O2. Ru films were annealed in a reducing forming gas (4% H2 in N2) environment as well as an inert pure N2 environment at 400, 450, and 500C for various times. Resistivity is characterized via 4-pt probe, roughness via atomic force microscopy (AFM, crystallite size via x-ray diffraction (XRD), thickness and density via x-ray reflectivity (XRR), and composition via x-ray photoelectron spectroscopy (XPS). In addition, ruthenium-insulator-semiconductor (MOS) capacitors were used to extract the effective work function of the Ru. We find that post-deposition annealing reduces resistivity. For 500 C annealing in a 4% H2 / N2 ambient, resistivity was reduced from an as-deposited value of ~15 µΩ-cm to less than 10 µΩ-cm after 30 minutes and ~9 µΩ-cm after 60 mi, closely approaching the bulk value. These results indicate that ALD of Ru using Ru(DMBD)(CO)3 & O2 appears very promising for microelectronics applications. R. W. Powell, R. P. Tye, and J. Woodman Margaret, Platin. Met. Rev., 6, 138–143 (1962).D. Z. Austin et al., Chem. Mater., 29, 1107–1115 (2017).

High sensitivity Rutherford backscattering spectrometry using multidetector digital pulse processing

Rutherford backscattering spectrometry is a primary reference method for the quantity of materials, but has a limit-of-detection (LOD) presently at ∼1015 at/cm2 for analyses with traceable accuracy near 1%. A multidetector assembly is demonstrated which increases the count rate without decreasing the signal/noise due to pulse pile-up. A LOD of 6 × 1012 at/cm2 is achieved with the multidetector assembly and applied to quantify the onset of an atomic layer deposition (ALD) process for an in-depth study of the growth selectivity of ALD Ru on a-C:H and on SiCN. Besides, the spectrometer enables <10 min measurements on a Ru layer of 2.7 nm, permitting wafer mapping.

Area-selective atomic layer deposition of Ru on electron-beam-written Pt(C) patterns versus SiO2 substratum

Area selectivity is an emerging sub-topic in the field of atomic layer deposition (ALD), which employs opposite nucleation phenomena to distinct heterogeneous starting materials on a surface. In this paper, we intend to grow Ru exclusively on locally pre-defined Pt patterns, while keeping a SiO2 substratum free from any deposition. In a first step, we study in detail the Ru ALD nucleation on SiO2 and clarify the impact of the set-point temperature. An initial incubation period with actually no growth was revealed before a formation of minor, isolated RuOx islands; clearly no continuous Ru layer formed on SiO2. A lower temperature was beneficial in facilitating a longer incubation and consequently a wider window for (inherent) selectivity. In a second step, we write C-rich Pt micro-patterns on SiO2 by focused electron-beam-induced deposition (FEBID), varying the number of FEBID scans at two electron beam acceleration voltages. Subsequently, the localized Pt(C) deposits are pre-cleaned in O2 and overgrown by Ru ALD. Already sub-nanometer-thin Pt(C) patterns, which were supposedly purified into some form of Pt(Ox), acted as very effective activation for the locally restricted, thus area-selective ALD growth of a pure, continuous Ru covering, whereas the SiO2 substratum sufficiently inhibited towards no growth. FEBID at lower electron energy reduced unwanted stray deposition and achieved well-resolved pattern features. We access the nucleation phenomena by utilizing a hybrid metrology approach, which uniquely combines in-situ real-time spectroscopic ellipsometry, in-vacuo x-ray photoelectron spectroscopy, ex-situ high-resolution scanning electron microscopy, and mapping energy-dispersive x-ray spectroscopy.

Selective Ru ALD as a Catalyst for Sub-Seven-Nanometer Bottom-Up Metal Interconnects

Integrating bottom-up area-selective building-blocks in microelectronics has a disruptive potential because of the unique capability of engineering new structures and architectures. Atomic layer deposition (ALD) is an enabling technology, yet understanding the surfaces and their modification is crucial to leverage area-selective ALD (AS-ALD) in this field. The understanding of general selectivity mechanisms and the compatibility of plasma surface modifications with existing materials and processes, both at research and production scale, will greatly facilitate AS-ALD integration in microelectronics. The use of self-assembled monolayers to inhibit the nucleation and growth of ALD films is still scarcely compatible with nanofabrication because of defectivity and downscaling limitations. Alternatively, in this Research Article, we demonstrate a straightforward H2 plasma surface modification process capable of inhibiting Ru ALD nucleation on an amorphous carbon surface while still allowing instantaneous nucleation and linear growth on Si-containing materials. Furthermore, we demonstrate how AS-ALD enables previously inaccessible routes, such as bottom-up electroless metal deposition in a dual damascene etch-damage free low-k replacement scheme. Specifically, our approach offers a general strategy for scalable ultrafine 3D nanostructures without the burden of subtractive metal patterning and high cost chemical mechanical planarization processes.

Initial and steady-state Ru growth by atomic layer deposition studied by in situ Angle Resolved X-ray Photoelectron Spectroscopy

The clear substrate-dependent growth and delayed film continuity are essential challenges of Ru atomic layer deposition (ALD) demanding adequate and versatile approaches for their study. Here, we report on the application of in situ Angle Resolved X-ray Phototelectron Spectroscopy (ARXPS) for investigation of initial and steady-state ALD growth of Ru using Ru(EtCp)2 and O2 as precursors. Using ARXPS surface analysis technique we determine such parameters of Ru ALD initial growth as incubation period, fractional coverage and the thickness of islands/film depending on the substrate chemical state, governed by the presence/absence of NH3/Ar plasma pretreatment. It was demonstrated that NH3/Ar plasma pretreatment allows to obtain the lowest incubation period (∼7 ALD cycles) resulting in a continuous ultrathin (∼20Å) and smooth Ru films after 70 ALD cycles. In situ XPS at UHV was used at steady state Ru growth for analysis of half-cycle reactions that revealed formation of RuOx (x≈2) layer with thickness of ∼8Å after O2 pulse (first half-cycle). It was also shown that oxygen of RuOx layer combusts Ru(EtCp)2 ligands in the second half-cycle reaction and the observed Ru growth of ∼0.34Å per cycle is in a good agreement with the amount of oxygen in the RuOx layer.

Doping of Graphene By Atomic Layer Deposition of Ruthenium

Graphene has received enormous attention from both academia and industry owing to its excellent electrical, optical, chemical, and mechanical properties. A combination of properties makes graphene a strong candidate for the next generation of flexible and transparent conductive electrode (TCE) materials, but in practice the sheet resistance of a single, as-grown layer of graphene is still not sufficient for this purpose. One of the methods for creating highly conductive graphene films is to increase the charge carrier density through doping. Here, we propose a novel method of graphene doping based on atomic layer deposition (ALD). Ideally, adsorption of precursor should be suppressed on clean surface of graphene since the surface is inert without dangling bonds and chemically active functional group. Defects (e.g., grain boundaries, wrinkles, cracks, holes and residual material) work as selective nucleation sites. Ru is selected due to it having a well-established precursor and recipe and the difference in work function between graphene and Ru can also allow for work function tuning and carrier generation. The sheet resistance of graphene synthesized by chemical vapor deposition is found to be significantly reduced by the selective atomic layer deposition (ALD) of Ru onto defect sites such as wrinkles and grain boundaries. With 200 ALD cycles, the sheet resistance is reduced from ~500 Ω/sq to <50 Ω/sq and the p-type carrier density is drastically increased from 1013 cm-2 to 1015 cm-2. At the same time, the carrier mobility is reduced from ~670 cm2V-1s-1 to less than 100 cm2V-1s-1. This doping of graphene proved to be very stable, with the electrical properties remaining unchanged over 8 weeks of measurement. The selective deposition of Ru on defect sites also makes it possible to obtain a graphene film that is both highly transparent and electrically conductive (e.g., a sheet resistance of 125 Ω/sq with 92 % optical transmittance at 550 nm). The increase in the work function of graphene from 4.6 to 5.1 eV with Ru ALD provides clear evidence of hole carrier generation as a result of an electronic interaction between graphene and Ru. This demonstration of strong and stable doping of graphene with a high optical transmittance is therefore expected to contribute to the use of graphene as a TCE, and in other fields. Figure 1. Ru ALD on graphene. (a) TEM images of graphene after 20 cycles of Ru ALD. (b) Sheet resistance of graphene as a function of the number of ALD cycles. Inset of (b) shows sheet resistance as a function of time. Reference Minsu Kim et al, ACS Appl. Mater. Interfaces, Article ASAP Figure 1

Atomic Layer Deposition of Ruthenium and Ruthenium Oxide Using a Zero-Oxidation State Precursor

Atomic layer deposition (ALD) processes are reported for ruthenium (Ru) and ruthenium oxide (RuO2) using a zero-oxidation state liquid precursor, η4-2,3-dimethylbutadiene ruthenium tricarbonyl [Ru(DMBD)(CO)3]. Both ALD Ru and RuO2 films were deposited using alternating N2 -purge-separated pulses of Ru(DMBD)(CO)3 and O2. ALD Ru metal films were deposited via short (2 s) pulses of O2. Ru films have an ALD temperature window from 290 to 320 °C with a GPC of 0.067 nm/cycle and a negligible nucleation delay on SiO2. Ru films show a strong hexagonal crystal structure with low resistivity of approximately 14 μΩ cm at 320 °C. RuO2 films were deposited using longer (20 s) pulses of either molecular O2 or O2 plasma. RuO2 films deposited via thermal ALD using molecular O2 have a temperature window from 220 to 240 °C with a GPC and nucleation delay on SiO2 of 0.065 nm/cycle and 35 cycles, respectively. Thermal ALD RuO2 films show a distinct rutile phase microstructure with a resistivity of approximately 62 μΩ cm. In ...

Highly Stable and Effective Doping of Graphene by Selective Atomic Layer Deposition of Ruthenium.

The sheet resistance of graphene synthesized by chemical vapor deposition is found to be significantly reduced by the selective atomic layer deposition (ALD) of Ru onto defect sites such as wrinkles and grain boundaries. With 200 ALD cycles, the sheet resistance is reduced from ∼500 to <50 Ω/sq, and the p-type carrier density is drastically increased from 1013 to 1015 cm-2. At the same time, the carrier mobility is reduced from ∼670 to less than 100 cm2 V-1 s-1. This doping of graphene proved to be very stable, with the electrical properties remaining unchanged over eight weeks of measurement. Selective deposition of Ru on defect sites also makes it possible to obtain a graphene film that is both highly transparent and electrically conductive (e.g., a sheet resistance of 125 Ω/sq with 92% optical transmittance at 550 nm). Highly doped graphene layers achieved by Ru ALD are therefore expected to provide a viable basis for transparent conducting electrodes.

Bimetallic Nickel/Ruthenium Catalysts Synthesized by Atomic Layer Deposition for Low-Temperature Direct Methanol Solid Oxide Fuel Cells.

Nickel and ruthenium bimetallic catalysts were heterogeneously synthesized via atomic layer deposition (ALD) for use as the anode of direct methanol solid oxide fuel cells (DMSOFCs) operating in a low-temperature range. The presence of highly dispersed ALD Ru islands over a porous Ni mesh was confirmed, and the Ni/ALD Ru anode microstructure was observed. Fuel cell tests were conducted using Ni-only and Ni/ALD Ru anodes with approximately 350 μm thick gadolinium-doped ceria electrolytes and platinum cathodes. The performance of fuel cells was assessed using pure methanol at operating temperatures of 300-400 °C. Micromorphological changes of the anode after cell operation were investigated, and the content of adsorbed carbon on the anode side of the operated samples was measured. The difference in the maximum power density between samples utilizing Ni/ALD Ru and Pt/ALD Ru, the latter being the best catalyst for direct methanol fuel cells, was observed to be less than 7% at 300 °C and 30% at 350 °C. The improved electrochemical activity of the Ni/ALD Ru anode compared to that of the Ni-only anode, along with the reduction of the number of catalytically active sites due to agglomeration of Ni and carbon formation on the Ni surface as compared to Pt, explains this decent performance.

Atomic layer deposited self-forming Ru-Mn diffusion barrier for seedless Cu interconnects

Ru-based alloy thin films were prepared by atomic layer deposition (ALD) at a deposition temperature of 225 °C for use as a diffusion barrier for seedless Cu interconnects. Ru-Mn alloy thin films were grown by a repetition of super-cycles consisting of multiple Ru and Mn ALD sub-cycles. Ru and Mn ALD was performed using a sequential supply of a Ru precursor [1-Isopropyl-4-methylbenzene (cyclohexa-1, 3-diene) Ru (0)] and NH3 plasma, and a Mn precursor [bis(1,4-di-isopropyl-1,3-diazabutadienyl)Mn(II)] and H2 plasma, respectively. Secondary ion mass spectrometry (SIMS) indicated that Mn had been incorporated successfully into the Ru film by the periodic addition of Mn ALD sub-cycles during the ALD-Ru process. Plan-view transmission electron microscopy (TEM) showed that the grain size was reduced obviously from ∼15 nm (pristine Ru) to ∼8 nm (Ru-Mn alloy) and continuous columnar grain growth of the ALD-Ru film was prevented by the addition of the periodic Mn ALD sub-cycles. After annealing at 500 °C, the formation of a MnSiOx diffusion barrier was observed between the Ru-Mn film and underlying SiO2 surface by both cross-sectional view TEM and energy dispersive spectroscopy analysis and confirmed by SIMS depth profile. X-ray diffraction showed that the ultrathin ALD Ru-Mn thin film (∼5 nm) prevented Cu diffusion up to an annealing temperature of 600 °C, whereas the ALD-Ru thin film with the same thickness failed to prevent Cu diffusion only after annealing at 500 °C. Finally, the capability of the direct plating of Cu was demonstrated on the annealed ALD Ru-Mn film.

Low Temperature ABC-Type Ru Atomic Layer Deposition through Consecutive Dissociative Chemisorption, Combustion, and Reduction Steps

Thermal atomic layer deposition (ALD) of noble metals is frequently performed using molecular oxygen as the nonmetal precursor to effect combustion-type chemistry at relatively high temperatures of 300 °C. Bis(ethylcyclopentadienyl)ruthenium (Ru(EtCp)2) is one of the commonly used metal precursors for Ru ALD. Using Ru(EtCp)2 and oxygen as reactants, Ru ALD was achieved at near 300 °C. Here, we demonstrate that Ru ALD can proceed at as low as 150 °C by using successive exposures to oxygen and hydrogen as the coreactants. In situ quartz crystal microbalance (QCM) and quadrupole mass spectroscopy (QMS) measurements both suggest that this ABC-type ALD occurs through dissociative chemisorption, combustion, and reduction for the Ru(EtCp)2, oxygen, and hydrogen steps, respectively, in a similar manner to processes using ozone and hydrogen as coreactants reported previously. Moreover, we believe this molecular O2 and H2 based ABC-type ALD could be exploited for the ALD of other noble metals to decrease the deposi...

Atomic layer deposition of ruthenium surface-coating on porous platinum catalysts for high-performance direct ethanol solid oxide fuel cells

Pt–Ru bi-metallic catalysts are synthesized by atomic layer deposition (ALD) of Ru surface-coating on sputtered Pt mesh. The catalysts are evaluated in direct ethanol solid oxide fuel cells (DESOFCs) in the temperature range of 300–500 °C. Island-growth of the ALD Ru coating is confirmed by transmission electron microscopy and X-ray photoelectron spectroscopy (XPS) analyses. The performance of the DESOFCs is evaluated based on the current–voltage output and electrochemical impedance spectroscopy. Genuine reduction of the polarization impedance, and enhanced power output with improved surface kinetics are achieved with the optimized ALD Ru surface-coating compared to bare Pt. The chemical composition of the Pt/ALD Ru electrode surface after fuel cell operation is analyzed via XPS. Enhanced cell performance is clearly achieved, attributed to the effective Pt/ALD Ru bi-metallic catalysis, including oxidation of CO by Ru, and de-protonation of ethanol and cleavage of C–C bonds by Pt, as supported by surface morphology analysis which confirms formation of a large amount of carbon on bare Pt after the ethanol-fuel-cell test.

The effects of (NH4)2Sx treatment on n-GaN MOS device with nano-laminated ALD HfAlOx and Ru gate stack

The effects of ammonium poly-sulfide, (NH4)2Sx, treatment on the surface of GaN metal oxide semiconductor (MOS) device with nano-laminated atomic layer deposition (ALD) HfAlOx gate dielectric and Ru gate electrode were investigated and compared with HCl pre-treatment. Compared with sample without sulfur (S) passivation, S-passivated sample shows improved surface roughness, increased capacitance, higher breakdown voltage, smaller frequency dependence, lower interface state density (Dit). It is found that (NH4)2Sx can remove native oxide and passivate the surface and interface states. Surface oxidation is suppressed due to higher strength in the NS bonds than that of the NO bonds. Further improvement is observed with increasing (NH4)2Sx treatment time.

Understanding the EOT–Jg degradation in Ru/SrTiOx/Ru metal–insulator–metal capacitors formed with Ru atomic layer deposition

The impact of different Ru precursors and/or deposition methods on the electrical characteristics of Ru/SrTiOx/Ru capacitors has been investigated. The observed increase of the leakage current density (Jg) and the equivalent oxide thickness (EOT) for ALD (atomic layer deposition) deposited Ru layers compared to PVD (physical vapor deposition) deposited ones was found to be caused by a SrRuTiOx layer formation at the SrTiOx/Ru interface aided by the presence of the oxygen co-reactant used during the ALD, regardless of the precursor used.

Atomic Layer Deposition of Ruthenium on Ruthenium Surfaces: A Theoretical Study

Atomic layer deposition (ALD) of ruthenium using two ruthenium precursors, i.e., Ru(C5H5)2 (RuCp2) and Ru(C5H5)(C4H4N) (RuCpPy), is studied using density functional theory. By investigating the reaction mechanisms on bare ruthenium surfaces, i.e., (001), (101), and (100), and H-terminated surfaces, an atomistic insight in the Ru ALD is provided. The calculated results show that on the Ru surfaces both RuCp2 and RuCpPy can undergo dehydrogenation and ligand dissociation reactions. RuCpPy is more reactive than RuCp2. By forming a strong bond between N of Py and Ru of the surface, RuCpPy can easily chemisorb on the surfaces. The reactions of RuCp2 on the surfaces are less favorable as the adsorption is not strong enough. This could be a factor contributing to the higher growth-per-cycle of Ru using RuCpPy, as observed experimentally. By studying the adsorption on H-terminated Ru surfaces, we showed that H can prevent the adsorption of the precursors, thus inhibiting the growth of Ru. Our calculations indicate that the H content on the surface can have an impact on the growth-per-cycle. Finally, our simulations also demonstrate large impacts of the surface structure on the reaction mechanisms. Of the three surfaces, the (100) surface, which is the less stable and has a zigzag surface structure, is also the most reactive one.

Platinum–Ruthenium Heterogeneous Catalytic Anodes Prepared by Atomic Layer Deposition for Use in Direct Methanol Solid Oxide Fuel Cells

Heterogeneous Pt–Ru catalysts are synthesized by atomic layer deposition (ALD) of Ru onto a porous Pt mesh and employed as the anode in direct methanol solid oxide fuel cells (DMSOFCs). The degree of Ru coverage is controlled by the number of deposition cycles employed in catalyst preparation; samples are prepared using 50, 100, 200, 300, and 400 cycles. The dispersed nature of the ALD Ru coating is confirmed by auger electron spectroscopy and high-resolution transmission electron microscopy. DMSOFC performance is measured at several temperatures between 300 and 450 °C. Optimal ALD Ru coverage results in DMSOFC power and electrode impedance values close to ones from SOFCs with Pt electrodes running on hydrogen. Thermal stability is also improved significantly, preventing agglomeration of the Pt mesh. X-ray photoelectron spectroscopy is used to analyze the chemical properties of the surface and confirms that increased ALD Ru coverage results in a dramatic reduction in the amount of surface-bound carbon mon...

Ruthenium and ruthenium dioxide thin films deposited by atomic layer deposition using a novel zero-valent metalorganic precursor, (ethylbenzene)(1,3-butadiene)Ru(0), and molecular oxygen

Ruthenium (Ru) and ruthenium dioxide (RuO2) thin films were grown by atomic layer deposition (ALD) by applying a sequential supply of a novel zero-valent metalorganic precursor, (ethylbenzene)(1,3-butadiene)Ru(0) (EBBDRu, C12H16Ru), and molecular oxygen (O2) at a deposition temperature of 225°C. EBBDRu provided a high vapor pressure of 1.2Torr at 88°C. In the case of Ru ALD, the growth per cycle (GPC) was ∼0.06nm/cycle starting with a slight incubation period of approximately 15 ALD cycles on a thermally grown silicon dioxide initial substrate. A metallic Ru film with high purity and low resistivity (∼26μΩcm) was obtained at an ultra-thin thickness of ∼10nm. Furthermore, RuO2 thin films were grown controllably by increasing the O2 pulsing time at a pure O2 gas flow (with no nitrogen dilution) and at a deposition temperature of 225°C. The GPC in the case of RuO2 ALD was ∼0.09nm/cycle and the number of incubation cycles was as low as 6 on a SiO2 starting substrate. Both the Ru and RuO2 thin films exhibited excellent step coverage of ∼100% in very narrow trenches with 4.5 aspect ratio and a 25nm top opening.