WN Films Research Articles

Microstructure and corrosion properties of Al1-xWxN coatings for potential use in gas turbine blades

Herein, a numerical approach of Al1-xWxN thin film coatings on Inconel 738LC superalloys for thermal barrier applications has been studied and the experimental analysis includes deposition of Al1-xWxN films on Si (100), glass and transparent quartz substrates at 40 % N2 flow rate using a dual target DC reactive magnetron sputtering technique to investigate the morphology, microstructure, chemical bonding and corrosion behaviour. AFM analysis revealed the rms roughness, Sq and average roughness, Sa increased with the increasing W content from 22 to 70 at.%. It was found that Al1-xWxN films tend to form tiny valleys on the film surface because the values of surface skewness, Ssk lie below zero. The TEM image showed a branched snowflake structure for the specimen of Al0.58W0.42N films with discrete spots in the SAED pattern, confirming the microcrystalline nature. The blue-shifting of Ecorr towards positive potential confirmed the lower corrosion resistance of WN films than those of AlN. XRD spectra of Al0.58W0.42N films showed an amorphous nature devoid of peaks, which is also confirmed by the SAED pattern. The quasi-passive oxide layer formation was spontaneous for WN films compared to the AlN films. The bending vibrations of AlN and WN showed the coordination environment of the metal centre in the Al1-xWxN films. The computational results indicated that the thermal barrier properties of Al1-xWxN films decreased with the increasing W content, i.e., AIN > Al0.58 W0.42N > WN.

Tweaking the mechanical stability of Al1−xWxN ternary nitride alloys for hard coating applications, and study on their structural, photoluminescence and surface chemical analysis

This study focuses on the synthesis and achievement of ternary Al1−xWxN nitride films as hard coating materials. A dual-target DC reactive magnetron sputtering process was used to coat Al1−xWxN thin films on Si (100), glass, and transparent quartz substrates. The elemental analysis of the films was calculated by energy dispersion spectroscopy and the corresponding value of x changes from 0 to 1. The X-ray diffraction data showed a-axis orientation of the AlN films with hexagonal phase and amorphous nature for Al0.78W0.22N and Al0.58W0.42N films. Atomic force microscopy analysis showed that the surface morphology of Al0.78W0.22N films was better than that of AlN and Al0.3W0.7N films, as evidenced by the significantly lower root-mean-square roughness value of 1.79 nm compared to 5.78 and 13.9 nm, respectively. The resistivity of Al1−xWxN films was determined by a four-probe method and resulted in a record low value of 4.08 × 10−5 Ω-m for WN films. The photoluminescence emission spectra showed distinct peaks in the visible region at different wavelengths, and the deconvoluted blue emission peak was attributed to the native defects in the Al1−xWxN films. X-ray absorption spectroscopy data showed an increase in feature-a from Al0.78W0.22N to Al0.58W0.42N films, indicating stronger hybridization of N 2p with Al 3p and W 5d orbitals due to π * -resonance. The oxygen content calculated by X-ray photoelectron spectroscopy was 34.6, 35.39, and 19.74 at% on the surface of AlN, Al0.58W0.42N, and WN films, respectively. The surface oxidation of AlN films triggered the transfer of charge from nitrogen to oxygen on the surface of AlN films. The nanoindentation results showed that the Al0.3W0.7N films have hardness and elastic modulus of 17.84 GPa and 196.96 GPa, which are higher than those of the other Al1−xWxN films, while the AlN films have higher fracture toughness due to the reduction of contact pressure.

Sputter deposition of WNx thin films by helicon-wave-excited argon plasma with N2 seeding

—ungsten nitride (WN x ) films were deposited on silicon substrates by nitrogen gas (N 2 ) seeded helicon-wave-excited argon plasma sputtering at various N 2 flow rates (F N2 ), axial distances (Z) and substrate temperatures (T s ). For the substrates without extra heating (289–368 K), increasing F N2 (0–30 sccm) or Z (1.5–6 cm) can both increase the stoichiometry x = [N]/[W], causing a series of crystalline phase evolutions (α-W → β-W → fcc-W 2 N → hexagonal WN). This transition from metallic W to less conductive nitride state, brings about a wide range of the resistivity from 32 to 1941 μΩ-cm. Due to the solid solution hardening effect and the restraint of grain dislocation, the maximum hardness value of 32.2 GPa is obtained when a nanocomposite of β-W and fcc-W 2 N phases is formed. For the substrates with extra heating (Z = 1.5 cm, F N2 = 5 sccm), hexagonal phase WN 0.99 film with high crystallinity has been successfully synthesized at T s = 773 K. Increasing T s from 373 to 873 K, due to the release of the interstitial N atoms and the densification of the structure, the resistivity decreases from 1265 to 952 μΩ-cm and elastic modulus increases slightly from 297 to 329 GPa. The decomposition of the films deposited at various T s starts almost at the same temperature (950 K) followed by two typical N 2 desorption peaks related to the decomposition of W 2 N phase. With increasing T s , the peaks become weaker with a slight shift towards the high temperature region, indicating the improvement of thermal stability. • WN x thin films are deposited by Helicon-wave-excited argon plasma sputtering with N 2 seeding. • Well crystallized hexagonal phase WN films are synthesized. • Structure, composition, morphology, mechanical and electrical properties are investigated. • Films deposited with higher substrate temperature show improved thermal stability.

Water management implications for ALD-modified polymer electrolyte membrane fuel cell catalysts

Device testing of polymer electrolyte membrane fuel cell catalysts is essential for electrocatalyst development, yet most reported catalysts fabricated with nanoceramic coatings via atomic layer deposition (ALD) have not been thoroughly examined in this fashion. Platinum nanoparticle catalysts supported on functionalized XC72 carbon black that had been modified with sub-monolayer WN films and subjected to various thermal treatments were incorporated into membrane electrode assemblies and tested for oxygen reduction reaction activity in a fuel cell. The mass activities of the catalysts calculated at low current densities had comparable trends to those previously recorded in aqueous half-cell testing; however, significant deviations in catalyst performance became apparent at high current densities in the mass transport region of the polarization curves. The poor performance of the ALD-modified catalysts was attributed to water flooding induced by the low hydrophobicity of these catalyst layers, as determined by contact angle measurements on the cathode surfaces. It was seen that hydrophobicity was increased by thermal treatment and removal of surface groups known to be prone to hydrogen bonding, thereby improving the catalyst performance in the mass transport region. A heat-treated WN-coated ALD catalyst was found to have superior performance to commercial Pt/C. The field of research on fuel cell catalyst design via ALD is rapidly expanding, and this work demonstrates the importance of understanding the impact of ALD-deposited nanostructures on materials properties beyond the pure electrocatalytic activity.

Effects of deposition parameters on the structure and properties of ZrN, WN and ZrWN films

This paper examines optimal settings for deposition parameters for transition metal nitride (ZrN, WN and ZrWN) thin films that are deposited on tungsten carbide tools and glass substrates using direct current (DC) reactive sputtering with pure Zr and W metal targets and Ar plasma and $$\hbox {N}_{2}$$ reactive gases. Experiments using the grey-Taguchi method are conducted to study the effects of deposition parameters (substrate plasma etching time, $$\hbox {N}_{2}/(\hbox {N}_{2} + \hbox {Ar})$$ flow rate, deposition time and substrate temperature) on a film that is deposited on a cutting tool that is used for dry machining and on the films’ mechanical properties. The substrates’ surfaces are etched using oxygen plasma pretreatment. It is clear that the coated film is homogeneous, very compact and exhibits perfect adherence to the substrate. The results of grey relational analysis show for the dry turning AISI 304 stainless steel that the surface roughness is approximately $$R_{\mathrm{a}} = 0.70\, \, \upmu \hbox {m}$$ and that the flank wear is approximately $$14.02 \, \,\upmu \hbox {m}$$ . The grey relational analysis shows that the period for which the substrate (tungsten carbide tool) is under plasma-etched pretreatment has the most significant effect on both the surface roughness and flank wear. The coated films are analysed using scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), transmission electron microscopy (TEM), X-ray diffraction and a nano-indenter. The ternary nitride (ZrWN)-coated specimens exhibit better mechanical properties than binary nitride (ZrN and WN) specimens. The optimum ZrWN coating exhibits the greatest hardness (H), elastic modulus (E) and H / E values.

Removal of atrazine by photoelectrocatalytic process under sunlight using WN-codoped TiO2 photoanode

The present study was focused on the degradation of Atrazine (ATZ) and major by-products (DEA, DIA, DEDIA and ATZ-OH) from water by photoelectrocatalytic (PEC) oxidation process under solar light. The undoped TiO2, sub-stoichiometric TiO2 (TiO2−x) and codoped TiO2 (TiO2:WN) photoanodes were prepared by means of a radio frequency magnetron sputtering (RF-MS) deposition process. The X-ray photoelectron spectra (XPS) analysis shows that the N and W atoms were incorporated into the O and Ti lattice sites of TiO2 respectively (case of TiO2:WN film), while the XPS measurements of the TiO2−x films composition was determined to be TiO1.9. The UV–Vis transmittance spectra shows that in the case of the TiO2:WN films, the presence of nitrogen and tungsten improve the optical response of TiO2 under visible range compare to the presence of oxygen vacancies in to the TiO2−x films. The experimental results under solar light with an initial concentration of ATZ (100 µg L−1) show that after 180 min of treatment, the degradation of ATZ were 34.98%, 68.57% and 94.33% using TiO2, TiO2−x and TiO2:WN photoanodes, respectively. These results of ATZ degradation proved that TiO2:WN photoanode was more photoactive under solar light. The evolution by-products of ATZ under sunlight show that the principal mechanism of ATZ degradation was the oxidation of alkyl side chain and dealkylation.

In-situ co-doping of sputter-deposited TiO2:WN films for the development of photoanodes intended for visible-light electro-photocatalytic degradation of emerging pollutants

We report on the magnetron sputtering deposition of in-situ codoped TiO2:WN films intended for electro-photocatalytic (EPC) applications under solar irradiation. By varying the RF-magnetron sputtering deposition parameters, we were able to tune the in-situ incorporation of both N and W dopants in the TiO2 films over a wide concentration range (i.e., 0–9 at. % for N and 0–3 at. % for W). X-ray photoelectron spectroscopy analysis revealed that both dopants are mostly of a substitutional nature. The analysis of the UV-Vis transmission spectra of the films confirmed that the optical bandgap of both TiO2:N and TiO2:WN films can be significantly narrowed (from 3.2 eV for undoped-TiO2 down to ∼2.3 eV for the doped ones) by tuning their dopant concentrations. We were thus able to pinpoint an optimal window for both dopants (N and W) where the TiO2:WN films exhibit the narrowest bandgap. Moreover, the optimal codoping conditions greatly reduce the recombination defect state density compared to the monodoped TiO2:N films. These electronically passivated TiO2:WN films are shown to be highly effective for the EPC degradation of atrazine (pesticide pollutant) under sunlight irradiation (93% atrazine degraded after only 30 min of EPC treatment). Indeed, the optimally codoped TiO2:WN photoanodes were found to be more efficient than both the undoped-TiO2 and equally photosensitized TiO2:N photoanodes (by ∼70% and ∼25%, respectively) under AM1.5 irradiation.

Lifetime Enhancement of Visible Light Induced Photocharges in Tungsten and Nitrogenin situCodoped TiO2:WN Thin Films

We report on one-step in situ codoped TiO2 thin films synthesized by cosputtering. The purpose of this acceptor–donor passivated codoping approach is to overcome the optoelectronic limitations that arise for monodoped TiO2 in photocatalytic applications. To evaluate these added benefits, the TiO2:WN thin films were characterized by different techniques. X-ray diffraction patterns and X-ray photoelectron spectral analysis revealed that both N and W dopants are mostly present in the desired substitutional locations. Additionally, the codoping approach was found to reduce the internal strain and defect density of the TiO2:WN films as compared to their monodoped TiO2:N counterparts. This defect reduction is confirmed via photocharge lifetime variation obtained using visible light flash photolysis time-resolved microwave conductivity measurements (FP-TRMC). Photocharge lifetime analysis indicated the presence of three distinct decay processes: charge trapping, recombination, and surface reactions. These charac...

Thermal stability studies of tungsten nitride thin films

Superior mechanical properties, such as hardness of high level along with thermal stability are of great technological interests for cutting tools and other industrial applications. In this work, we present performance and stability of tungsten nitride (WN) film at a wide temperature range (RT – 600°C). WN films were deposited on silicon (100) substrates using reactive RF magnetron sputtering. The deposited samples were annealed at 200, 400 and 600°C for 2 h. Structural, electrical and mechanical properties of the films were analysed via X-ray diffraction, four-probe resistivity and nano-indentation test, respectively. XRD results show the formation of pure W2N crystalline phase. The change in microstructural parameters were investigated and found to be varying with annealing temperature. The electrical measurement result shows the decrease in resistivity with an increase in annealing temperature. Nano-indentation experiments reveal that the mechanical behaviour (hardness and elastic modulus) at different load are quite stable in the studied temperature range.

Electronic and optical properties of rocksalt-phase tungsten nitride (B1-WN)

The optical and electronic properties of rocksalt structure tungsten nitride (B1-WN) were investigated by x-ray photoelectron spectroscopy (XPS) and UV–visible-Fourier transform infrared optical reflectivity. Both 111-textured polycrystalline and epitaxial WN(111) films with [N]/[W] ratios of 1.12 and 0.87, respectively, were found to be electron conductors with partially filled W-5d conduction bands. However, their electronic behavior is dominated by high conduction electron losses, which are attributed to scattering at both anion and cation vacancies and are more pronounced for films with high nitrogen content, yielding high resistivity values of 1.4–2.8 mΩ cm. The dielectric function is well described with a Drude–Lorentz model over a large wavelength range from 0.2 to 100 μm, and exhibits an ε1 that becomes negative above a relatively high critical wavelength that increases with increasing nitrogen content from 22 to 100 μm. Compositional interpolation of XPS data provides a W4f7/2 electron binding energy for pure stoichiometric B1-WN of 31.9 eV, while increasing the N-content results in a reduction of the density of states from the W-5dt2g bands at and near the Fermi level. The overall results do not confirm the predicted promising plasmonic properties of B1-WN but instead reveal possible alternative applications for this compound as photothermal or epsilon-near-zero material.

Plasma-enhanced atomic layer deposition of tungsten nitride

Tungsten nitride (WN) has potential as an interconnect barrier film. Deposition of WN films with bis(tert-butylimido)bis(dimethylamido)tungsten utilizing plasma-enhanced atomic layer deposition has been investigated over a temperature range of 100–400 °C employing N2, H2/N2, and NH3 remote plasmas. Spectroscopic ellipsometry has been used to determine film thickness and optical properties. Film growth rate varied from 0.44 to 0.65 Å/cycle. Chemical composition was investigated with x-ray photoelectron spectroscopy. W:N ratios varied from 0.95:1 to 3.76:1 and carbon levels were sub-2% for atomic layer deposition conditions. Resistivity measurements, derived from four-point probe measurements, indicate higher deposition temperature and gas flow rates produce the lowest resistivity films. The lowest resistivity film of the study, which measured 405 μΩ cm, was deposited with a hydrogen-rich H2/N2 plasma at 400 °C.

MOCVD of tungsten nitride thin films: Comparison of precursor performance and film characteristics

Two different all nitrogen coordinated tungsten complexes, [W(NtBu)2(NMe2)2] (1) and [W(NtBu)2(NMe2){(iPrN)2C(NMe2)}] (2) were compared for metal organic chemical vapour deposition (MOCVD) of tungsten nitride (WN) thin films in a state‐of‐the‐art commercial MOCVD reactor. Precursor performances of both complexes were investigated under single source precursor (SSP) conditions and in the presence of ammonia as reactive gas where WN thin films were deposited on Si (100) substrates in a temperature range of 500–800 °C. The X‐ray diffraction (XRD) analysis showed that the films deposited under SSP conditions contained a mixture of carbide and nitride phases; while upon the addition of ammonia crystalline WN thin films were formed at higher temperatures (T ≥ 600 °C). Elemental composition investigated by complementary techniques such as Rutherford backscattering spectrometry (RBS), nuclear reaction analysis (NRA) and X‐ray photoelectron spectroscopy (XPS) revealed that the films grown in the presence of ammonia had increased levels of nitrogen and a decreased carbon content in comparison to films grown under SSP conditions. WN films deposited in the presence of ammonia show higher resistivity values than those deposited under SSP conditions.

Investigation of Tungsten Nitride Deposition Using Tungsten Hexafluoride Precursor for Via and Plug Metallization

We investigated a tungsten nitride (WN)-based diffusion barrier layer (DBL) on a Cu metal layer by atomic layer deposition (ALD) using three different treatments, namely, ammonia (NH3) plasma treatment, ammonia (NH3) pulsed plasma treatment, and diborane (B2H6) pulsed gas injection treatment. In an experimental result of a method with B2H6 pulsed gas injection, the fluorine (F) concentration was below 3% in the WN films, and optimum growth conditions, including a linear deposition rate, a few incubation cycles, good thermal stability, and an excellent step coverage of approximately 100%, were observed for the DBL application. These results suggest that the B2H6 pulsed gas injection is a useful method for obtaining high-quality WN films for use as a DBL on a Cu contact via a 15 nm node.

Stress control of sputtered W film using W/WN multilayer

For the purpose of enhancement of productivity by reducing opportunity of preventive maintenance, it is very important to form a tungsten and tungsten-nitride pasting layer onto the chamber wall inside a tungsten sputter deposition system. In this study, looking for the optimum usage condition of reactive sputter facility, we controlled the stress levels of both of W and WN films by utilization of change of gas composition and operating pressure. The stress of W film was changed from tensile to compressive with decreasing the working pressure during deposition. And the WN film showed compressive stress, which follows a linear behavior by increasing N2/Ar ratio. Sputter deposited tungsten film applied to the metal gate often showed high tensile stress of ~2000MPa. Based on an experimental data, we found that stacked W/WN films with various stress levels could be steadfastly built-up and stability of adhesions of these films was quantitatively measured by scratch tester. From this adhesion test, it was observed that the optimized W/WN multilayer stack could be persistently maintained by compensating the tensile stress of W layer, which suppresses the delamination of films. Based on the above experimentally observed facts, we could suppress the particle generation resulting in chamber contamination, and thus improve productivity by elongating the period of non-stopping use of process chamber.

Initial growth of W‐based films deposited on Si studied with ARXPS

AbstractW and WN films with thicknesses of less than one monolayer up to some nanometers were deposited by magnetron sputtering. The samples were transferred after deposition immediately into an analysis chamber without breaking the vacuum to avoid oxide formation and contamination. Analysis was done by means of XPS for elemental and bonding state characterization and angle‐resolved XPS (ARXPS) for nondestructive depth profiling. Phase formation and morphology were studied during the first stages of layer growth. Influences of the residual gas atmosphere are discussed. Copyright © 2008 John Wiley & Sons, Ltd.

Growth of nitrogen doped ZnO films through a nitrogen diffusion process from WN films formed by a cosputtering technique

High quality nitrogen doped ZnO films were fabricated on glass substrates by allowing nitrogen atoms from a pregrown tungsten nitride (WN) to be activated and diffused into a pure ZnO film during an in situ post-thermal annealing process. The N doped ZnO film exhibited reproducible electrical properties including a Hall concentration of 3.69×1018 cm−3, a mobility of 1.35 cm2/Vs , and a resistivity of 10 Ω cm at room temperature, along with corresponding structural results. Further investigation using ZnO p-n homojunctions, which displayed good I-V characteristics with a turn-on voltage of about 3 V, demonstrated that the p-type ZnO growth process can simply form p-type ZnO:N.

Zirconium-Doped Tantalum Oxide Gate Dielectric Films Integrated with Molybdenum, Molybdenum Nitride, and Tungsten Nitride Gate Electrodes

Electrical properties of zirconium-doped tantalum oxide (Zr-doped ) high- gate dielectric films integrated with Mo, MoN, and WN gate electrodes were studied. The Zr-doped film with the ratio of 0.33, which showed good dielectric properties in previous studies, was used as the high- film in this study. A single metallic alloy target was used for the sputter deposition. The resistivities of the MoN and WN films were minimized by adjusting the concentration in the sputtering gas, i.e., 10% (90% Ar) for MoN and 2.5% for WN, respectively. Microstructures of the gate electrodes were investigated with X-ray diffraction. Current density, equivalent oxide thickness, breakdown strength, flatband voltage, hysteresis, interface state density, and frequency dispersion of capacitors with different gate electrode materials were analyzed and compared. Device characteristics changed drastically with the gate electrode material, mainly due to the difference in work functions.

Diffusion barrier properties of tungsten nitride films grown by atomic layer deposition from bis(tert-butylimido)bis(dimethylamido)tungsten and ammonia

Highly uniform, smooth, and conformal coatings of tungsten nitride (WN) were synthesized by atomic layer deposition (ALD) from vapors of bis(tert-butylimido)bis(dimethylamido)tungsten and ammonia. The films are shiny, silver colored, and electrically conducting. The films were amorphous as deposited. 100% step coverage was obtained inside holes with aspect ratios greater than 40:1. WN films as thin as 1.5 nm proved to be good barriers to diffusion of copper for temperatures up to 600 °C. Annealing for 30 min at temperatures above 725 °C converted the WN to pure, polycrystalline tungsten metal. ALD of copper onto the surface of the WN produced strongly adherent copper films that could be used as “seed” layers for chemical vapor deposition or electrodeposition of thicker copper coatings.

Electrical and chemical characterization of W/sub 1-x-y/Si/sub x/N/sub y/ (0≤x≤0.42, 0≤y≤0.30) Schottky diodes for self-aligned gate GaAs MESFETs

WSiN Schottky diodes on GaAs have been electrically and chemically characterized for atomic silicon and nitrogen; compositions of 0 to 42% and 0 to 28%, respectively. It is found that the main cause for Schottky diode degradation, after high temperature annealing, is the out-diffusion of As from GaAs. For films with atomic nitrogen composition of /spl ges/5%, As outdiffusion is eliminated as long as the atomic Si composition is /spl les/40%. WN films (5% nitrogen) were applied to the fabrication of self-aligned gate lightly doped drain MESFET's with buried P layer. A maximum transconductance, g/sub m/, of 370 mS/mm, f/sub T/ of 33 GHz, and DCFL inverter delay of 29 ps are measured for a 0.5 /spl mu/m gate technology. >

Reactive-ion-beam-sputtered WNx films on silicon: Growth mode and electrical properties

WN films were deposited on clean Si(100) substrates via reactive-ion-beam sputtering a W target by a nitrogen ion beam in an UHV system. The energy of the incident ions varied in the range of 0.250 to 3 keV. The growth mode dependence of the films on the nitrogen ion energy was studied by in situ Auger electron spectroscopy measured as a function of coverage. Nitridation of the Si at the first stage of deposition has been found. This nitridation was more pronounced for the lower N beam energies, and minimal for the 2 keV beam. A similar trend was observed for the bulk film composition. In a complementary way, the dependence of electrical properties of the WN/Si junctions on the nitrogen energy has been studied. A higher barrier height on p-type Si than on n-type Si was found, unlike the expectation for regular metallization of W and its compounds on Si. The electrical characteristics can be attributed to the deposition technique. For the low-energy beams, the formation of the interfacial layer was probably dominating, while at higher energies radiation damage and possibly also N implantation played a more important role.