Tungsten Films Research Articles

Correlation between atomic composition and gas sensing properties in tungsten–iron oxide thin films

Abstract Mixed tungsten and iron oxide thin films were prepared with reactive RF sputtering. The electrical response of thin films of W–Fe oxides toward CO, NO 2 , ozone and ethanol was investigated. Moreover, XPS technique was employed to study the chemical composition of the samples’ surfaces and the depth profile through the whole thickness of the films. The oxidation states of W and Fe were determined from the photoelectron spectra. Iron addition always increases the response towards ozone, carbon monoxide and ethanol. For nitrogen dioxide, the introduction of iron concentrations lower than 10% produce an enhancement in the response.

Reactive Ion Etching of Titanium Tungsten Thin Films

Reactive ion etching processes on titanium tungsten thin films have been investigated with , , and feed gases. Process parameters such as feed gas composition, radio-frequency power, and pressure showed tremendous effects on the etch rate and the etch selectivity. Both F and Cl are effective etchants for the titanium tungsten film. The etch rate is chemically controlled by the F concentration in the plasma, and by the sum of Cl and F concentrations in the and plasmas. The etch rate is a function of both the plasma phase etchant concentration and the ion bombardment energy. The peak etch rate was obtained at the medium pressure range, e.g., , due to the combination of the above two factors. The F residue was detected on the plasma etched surface, while a trace amount of Cl was detected on the plasma etched surface. Although the plasma-enhanced chemical vapor deposition silicon nitride was etchable with the same type of plasma, an etch selectivity of greater than 2 was achieved under the low ion bombardment condition.

Electrodeposition of metallic tungsten films in ZnCl 2–NaCl–KCl–KF–WO 3 melt at 250 [formula omitted

WO 3 hardly dissolved in ZnCl 2–NaCl–KCl (0.60:0.20:0.20, in mole fraction) melt at 250 ° C. The solubility of WO 3 increased by the addition of KF to the melt, which enabled electrodeposition of metallic tungsten. A smooth and fine film of metallic tungsten was obtained on a nickel substrate by the potentiostatic electrolysis at 0.06 V versus Zn(II)/Zn. The thickness reached ca. 2.5 μ m after 6-h electrolysis. The surface of the nickel contact probe pin manufactured by the conventional LIGA (Lithographie-Galvanoformung-Abformung, German abbreviation) process was successfully coated with a smooth and adhesive tungsten film by using this melt.

Mechanical Properties of Thin Films and Nanometric Multilayers Using Tensile Testing and Synchrotron X‐Ray Diffraction

AbstractX‐Ray diffraction (XRD) in combination with tensile testing is a very attractive tool for investigating the elastic behavior and further fracture or plasticity of metallic thin films and multilayers. Such studies are carried out with synchrotron X‐ray sources allowing for several diffraction and loading conditions to be investigated and hence for great precision to be achieved. XRD is phase selective and allows for the study of individual layers or phase contributions. The method is based on a length scale change to relate in‐grain elastic strains to tensile macro‐stresses. Hence, it requires the modeling of the grain interactions in view of the structure of the films (morphology, texture). The paper is illustrated with studies carried out on elastically isotropic tungsten (W) films, elastically anisotropic gold (Au) textured films, and nanometric tungsten/copper (W/Cu) multilayers.magnified image

Pulsed Laser-Induced Effects in the Material Properties of Tungsten Thin Films

In this work we present evidence of photo-induced effects on crystalline Tungsten (W) films. A frequency doubled Nd:YAG (5ns) laser was used in our experiments. The W thin films were deposited on silicon substrates by the DC-sputtering technique using W (Lesker, 99.95% purity) targets in an argon atmosphere. The crystalline phase of the deposited W films was determined by X-ray diffraction. Our experimental results show clear evidence that several events take place as a consequence of exposure of the W films to the laser nanosecond pulses. One of those events has a chemical effect that results in a significant degree of oxidation of the film; a second event affects the structural nature of the initial W material, resulting into a material phase change; and a third event changes the initially homogeneous morphology of the film into an unexpected porous material film. As it has been confirmed by the experiments, all of these effects are laser fluence dependent. A full post exposure analysis of the W thin films included Energy Dispersive Spectrometry to determine the degree of oxidation of the W film; a micro-Raman system was used to explore and to study the transition of the crystalline W to the amorphous-crystalline WO3 phase; further analysis with Scanning Electron Microscopy showed a definite laser-induced porosity which changes the initial homogeneous film into a highly porous film with small features in the range from 100 to 300 nm.

Tungsten doped vanadium dioxide thin films prepared by atmospheric pressure chemical vapour deposition from vanadyl acetylacetonate and tungsten hexachloride

The atmospheric pressure chemical vapour deposition reaction of vanadyl acetylacetonate and tungsten hexachloride led to the production of thin films of tungsten doped monoclinic vanadium dioxide on glass substrates. Scanning electron microscopy indicated that the films had a columnar island growth morphology. Transmission and reflectance measurements elucidated a significant change in properties in the IR portion of the spectrum either side of the metal to semiconductor transition. Variable temperature transmission studies show that the metal to semiconductor transition was lowered by doping tungsten into the films and that this effect was dependent on the amount of tungsten doping.

A Study on the Electrochemical and the Chemical Mechanical Polishing Behaviors of W and Ti Film

In this paper, the chemical mechanical polishing (CMP) performances of tungsten (W) and titanium (Ti) films according to the oxidizer content were studied through an electrochemical corrosion analysis. In order to investigate the electrochemical polishing behavior of the W and the Ti films, we used an alumina (Al2O3)-based tungsten slurry with a H2O2 oxidizer for CMP test. As an experimental result, for the case of 5 vol% added oxidizer, the removal rates were improved, and a good polishing selectivity of 1.4 : 1 was obtained, which means that the oxidizer with the highest removal rate has a high dissolution rate due to the predominant electrochemical corrosion effects. Therefore, we conclude that the CMP characteristics of W and Ti strongly depend on the amounts of H2O2 oxidizer added.

Analysis of tungsten film electrodeposited from a ZnCl 2–NaCl–KCl melt

Microparts for micro-electro-mechanical systems (MEMS) are becoming increasingly important, and the Lithographie Galvanoformung Abformung (LIGA) process for producing such parts is attracting attention [1]. However, as this process requires the step of electroplating in aqueous solution, only copper, nickel and their alloys can be used because of the limit of the potential window of water. We have been attempting to apply the electroplating of refractory metals in molten salts to the LIGA process or to the surface coating of conventional LIGA microparts in order to give higher strength and heat resistance for the microparts. Herein we report the characteristics of a tungsten film electrodeposited from a ZnCl 2–NaCl–KCl melt at 250 °C.

Doped and un-doped vanadium dioxide thin films prepared by atmospheric pressure chemical vapour deposition from vanadyl acetylacetonate and tungsten hexachloride: the effects of thickness and crystallographic orientation on thermochromic properties

The atmospheric pressure chemical vapour deposition reaction of vanadyl acetylacetonate and tungsten hexachloride with oxygen led to the production of thin films of tungsten doped monoclinic vanadium dioxide on glass substrates. Scanning electron microscopy and X-ray diffraction indicated that the films had different morphologies and crystallinities depending on the deposition conditions used. Transmission and reflectance measurements showed a significant change in properties in the near infra-red either side of the metal to semiconductor transition. Variable temperature transmission studies show that the metal to semiconductor transition was lowered by tungsten doping. The effect of film thickness was studied with un-doped and doped films. It was found that film thickness limited the intensity of light passing through the film and the extent of the thermochromic transition but was found not to influence the hysteresis width or temperature of transition. Different film growth conditions led to a range of film morphologies which profoundly affected the resulting optical properties of the films. It was found that film morphology and preferred crystallographic orientation had a marked influence on the width and switching temperature of the thermochromic transition.

The surface mapping and crystal orientation of body-centered cubic thin metal tungsten films of different thickness

The surface mapping and crystal orientation of body-centered cubic thin metal tungsten films of different thickness

Particles as Transport Carriers in CMP Slurries

ABSTRACTNanoparticles provide multiple functionalities to the performance of CMP slurries. These include mechanical surface abrasion, mass transport of slurry chemistries between the pad and wafer surface, or increased chemical reactivity of some key additives by in-situ interactions with the particles surfaces. Since most of the inorganic nanosized oxides used as common abrasives in CMP slurries (silica, alumina, ceria) have chemically reactive hydrophilic surface functionalities in a large pH range (2 – 12), we can assume that significant interactions between the inorganic particles surface and some of the slurry additives (organic surfactants, oxidizers, film-forming ligands, removal rates promoters, etc.) could have a meaningful impact on slurry ultimate performances (removal rates, planarity, defectivity, etc.)In this presentation we will highlight the significance of slurry abrasives as surface modified nanoparticles/chemical carriers, able to directly participate and control the metal oxidation/removal mechanism, removal rates and other polishing characteristics. We will discuss two relevant examples, both involving fumed silica as the carrier particle in two different low pH slurries of variable complexities in terms of design (with/without particles surface modifiers) and performance requirements for tungsten CMP. We will provide a complex variety of analytical evidence (TEM, SEM, FT-IR, GPC, cyclic voltammetry, MS-TOF) in order to support the proposed mechanism of “chemically activated fumed silica”, in its natural (no interactions with organic additives in the slurry) and surface modified form (in-situ interactions with organic additives), as a carrier of selective slurry components with enhanced chemical activity, that ultimately controls the tungsten CMP mechanism and the ability of the slurry to efficiently and predictably remove the oxidized tungsten film formed at the wafer surface.

Silicon MOS structures with nonstoichiometric metal-oxide semiconductors

MOS structures are formed by oxidative annealing of tin, tungsten, palladium, nickel, and zinc thin films on silicon, and their high-frequency C-V characteristics are measured. The energy spectra of the density of surface states taken of SnO2 − x, WO3 − x and PdOx nonstoichiometric oxides are found to have common features.

초고온 MEMS용 다결정 3C-SiC의 Ohmic Contact 특성

This paper describes the ohmic contact formation of polycrystalline 3C-SiC films deposited on thermally grown Si wafers. In this work, a TiW (titanium tungsten) film as a contact material was deposited by RF magnetron sputter and annealed with the vacuum process. The specific contact resistance (<TEX>${\rho}_{c}$</TEX>) of the TiW contact was measured by using the C-TLM (circular transmission line method). The contact phase and interfacial reaction between TiW and 3C-SiC at high-temperature as also analyzed by XRD (X-ray diffraction) and SEM (scanning electron microscope). All of the samples didn't show cracks of the TiW film and any interfacial reaction after annealing. Especially, when the sample was annealed at <TEX>$800^{\circ}$</TEX> for 30 min., the lowest contact resistivity of <TEX>$2.90{\times}10{\Omega}cm^{2}$</TEX> was obtained due to the improved interfacial adhesion. Therefore, the good ohmic contact of polycrystalline 3C-SiC films using the TiW film is very suitable for high-temperature MEMS applications.

Electrical conduction mechanisms in thermally evaporated tungsten trioxide(WO3) thin films

Thin films of amorphous tungsten trioxide,a-WO3, have been thermally evaporated onto glass substrate held at 350 K.Annealing at 723 K caused the formation of polycrystalline tungsten trioxide,c-WO3, with a monoclinic structure. The dark DC electrical conductivity of botha-WO3 and c-WO3 was studied over a temperature range from 298 to 625 K in two environmentalconditions (air and vacuum). A simple Arrhenius law, a polaron model and a variablerange hopping model have been used to explain the conduction mechanism fora-WO3 films. Using the variable range hopping model, the density of localized states at the Fermi level,N(EF), wasfound to be 1.08 × 1019 eV−1 cm−3. The mechanism of electrical conduction inc-WO3 films is explained by means of the Seto model. The Seto model parameters were determined as the energybarrier (Eb = 0.15 eV), the energy of trapping states with respect to the Fermi level(Et = 0.9 eV) and the impurityconcentration (ND = 4.05 × 1015 eV−1 cm−3). The thickness dependence of resistivity ofc-WO3 films has been found to decrease markedly with increasing film thickness, which is explained on thebasis of the effective mean free path model. Using this model, the mean free path of electrons inc-WO3 films was evaluated. The temperature dependence of the thermoelectric power fora-WO3 films reveals that our samples are n-type semiconductors.

A study on the correlation between electrochemical corrosion and chemical mechanical polishing performance of W and Ti film

In this paper, in order to investigate the electrochemical polishing behavior of the tungsten (W) and titanium (Ti) film, the chemical mechanical polishing (CMP) performances of W and Ti film according to the oxidizer contents were studied through electrochemical corrosion analysis. The alumina (Al 2O 3)-based tungsten slurry with H 2O 2 oxidizer was used for CMP test. As an experimental result, for the case of 5 vol% oxidizer added, the removal rates were improved and a good polishing selectivity of 1.4 : 1 was obtained. It means that the oxidizer with the highest removal rate (RR) has a high dissolution rate due to the predominant electrochemical corrosion effects. Therefore we conclude that the W and Ti-CMP characteristics are strongly dependent on the amounts of H 2O 2 oxidizer additive.

Indentation of a hard film on a soft substrate: Strain gradient hardening effects

The strain gradient work hardening is important in micro-indentation of bulk metals and thin metallic films, though the indentation of thin films may display very different behavior from that of bulk metals. We use the conventional theory of mechanism-based strain gradient plasticity (CMSG) to study the indentation of a hard tungsten film on soft aluminum substrate, and find good agreement with experiments. The effect of friction stress (intrinsic lattice resistance), which is important in body-center-cubic tungsten, is accounted for. We also extend CMSG to a finite deformation theory since the indentation depth in experiments can be as large as the film thickness. Contrary to indentation of bulk metals or soft metallic films on hard substrate, the micro-indentation hardness of a hard tungsten film on soft aluminum substrate decreases monotonically with the increasing depth of indentation, and it never approaches a constant (macroscopic hardness). It is also shown that the strain gradient effect in the soft aluminum substrate is insignificant, but that in the hard tungsten thin film is important in shallow indentation. The strain gradient effect in tungsten, however, disappears rapidly as the indentation depth increases because the intrinsic material length in tungsten is rather small.

Crystalline orientation and surface structure anisotropy of annealed thin tungsten films

The correlation between texture coefficient T 110 and surface structure anisotropy of thin metal film is constructed with an approach of integrating the discrete wavelet transform and fractal geometry concepts. The research is based on experimental results of tungsten films of different thickness that were deposited on an Si (100) substrate by magnetron sputtering and then annealed in vacuum at 400 °C for 1 h. The fact that there exists a definite relation between crystal orientation and surface morphology for the annealed W thin films suggests that the changes of film texture coefficient T 110 depend on the competition between strain energy and surface energy. This energy-depending evolution of surface structures of annealed W film is apparently a function of film's thickness.

Study on the delamination of tungsten thin films on Sb 2 Te 3

To investigate the reliability of electrode materials for chalcogenide random access memory (C-RAM) applications, the geometry and time evolution of the worm-like delamination patterns on a tungsten/Sb2Te3 bilayer system surface are observed by field emission scanning electronic microscope (FESEM) and optical microscopy. The tungsten film stress and interface toughness are estimated using a straight-side model. After confirming the instability of this system being due to large compressive stress stored in the tungsten film and relative poor interface adhesion, a preliminary solution as the inset of a TiN adhesion layer is presented to improve the system performances.

Stress and Moisture Effects on Thin Film Buckling Delamination

Deposition processes control the properties of thin films; they can also introduce high residual stresses, which can be relieved by delamination and fracture. Tungsten films with high 1–2 GPa compressive residual stresses were sputter deposited on top of thin (below 100 nm) copper and diamond-like carbon (DLC) films. Highly stressed films store large amounts of strain energy. When the strain energy release rate exceeds the films' interfacial toughness, delamination occurs. Compressive residual stresses cause film buckling and debonding, forming open channels. Profiles of the buckling delaminations were used to calculate the films' interfacial toughness and then were compared to the adhesion results obtained from the superlayer indentation test. Tests were conducted in both dry and wet environments and a significant drop in film adhesion, up to 100 times was noticed due to the presence of moisture at the film/substrate interface.

Application of Potential-pH Diagram and Potentiodynamic Polarization of Tungsten

The oxidizer-induced corrosion state and microstructure of surface passive metal-oxide layer greatly influenced on the removal rate of tungsten film according to the slurry chemical composition of different mixed oxidizers. In this paper, the actual polishing mechanism and pH-potential equilibrium diagram obtained from potentiodynamic polarization curve were electrochemically compared. An electrochemical corrosion effect implies that slurries with the highest removal rate (RR) have the high dissolution rate.