Showing papers on "Tungsten published in 1999"

Tungsten: Properties, Chemistry, Technology of the Element, Alloys, and Chemical Compounds

Abstract: The Element Tungsten: Its Properties. Tungsten History: From Genesis to the 20th Century Products. Important Aspects of Tungsten Chemistry. Tungsten Compounds and Their Application. Industrial Production. Tungsten Alloys. Tungsten and Tungsten Alloy Products. Tungsten in Melting Metallurgy. Tungsten in Hard Metals. Tungsten in Catalysis. Tungsten Scrap Recycling. Ecology. Economy. Tungsten and Living Organisms. Index.

Semiconductor metalization barrier

Abstract: A semiconductor metalization barrier, and manufacturing method therefor, is provided which is a stack of a cobalt layer and cobalt tungsten layer deposited on a copper bonding pad.

Nanocrystalline WC and WC/a-C composite coatings produced from intersected plasma fluxes at low deposition temperatures

Abstract: Low temperature vacuum deposition of tungsten carbide coatings, W1−yCy with compositions that varied from y=0 to 0.9, was investigated. Special attention was given to the production of nanocrystalline carbides with coatings of y>0.5. Previous attempts at producing WC with excess carbon at near room temperatures resulted in the formation of amorphous phases. In this study, crystalline WC was produced at 45 and 300 °C by the intersection of plasma fluxes from magnetron sputtering of tungsten and laser ablation of graphite. At both temperatures, formation of WC chemical bonding and nanocrystalline cubic β-WC1−x was observed using x-ray photoelectron spectroscopy and grazing angle x-ray diffraction when the carbon content was increased more than 30%. Increasing the substrate temperature to 300 °C did not affect the percentage of WC bonding, but it did promote considerable crystallization of cubic WC. As the carbon content was increased to more than 50%, a second phase consisting of amorphous carbon (a-C) was observed together with amorphitization of β-WC1−x. The a-C phase was identified as amorphous diamond-like carbon (DLC) by Raman spectroscopy. At 60–80 at. % C, a two phase structure was produced, which was composed of nanocrystalline β-WC1−x with 5–10 nm grains and amorphous DLC. The hardness of the WC/DLC composites was about 26 GPa based on nanoindentation tests. Correlation of the chemistry, microstructure, and mechanical properties of WC and WC/a-C coatings is discussed.

Trench structure substantially filled with high-conductivity material

Abstract: A trench structure that is substantially filled with high-conductivity material such as refractory metal particularly suitable for fast switching trench MOSFET applications. The trench is first lined by a dielectric material such as silicon dioxide. A layer of polysilicon is then formed on the dielectric material and provides buffering for stress relief. The trench is then filled substantially with refractory metal such as tungsten.

Effect of Particle Size during Tungsten Chemical Mechanical Polishing

Abstract: The size of the abrasive particles plays a critical role in controlling the polishing rate and the surface roughness during chemical mechanical polishing of interconnect materials during semiconductor processing. Earlier reports on the effect of particle size on polishing in silica show contradictory conclusions. To the best of our knowledge, a systematic study of the effect of particle size on tungsten polishing has not been published. This paper describes the controlled measurements that were conducted to determine the effect of alumina particle size during polishing of tungsten. Alumina particles of similar phase and shape with size varying from 0.1 to diam were used in these experiments. The polishing experiments showed that the local roughness of the polished surfaces was insensitive to alumina particle size. The removal rate was found to increase with decreasing particle size and increased solids loading. These results suggest that the removal rate mechanism is not a scratching type process, but may be related to the contact surface area between particles and polished surface controlling the reaction rate. ©1999 The Electrochemical Society

Tungsten chemical-mechanical polishing process using a fixed abrasive polishing pad and a tungsten layer chemical-mechanical polishing solution specifically adapted for chemical-mechanical polishing with a fixed abrasive pad

Abstract: The invention comprises tungsten chemical-mechanical polishing processes using fixed abrasive polishing pads, and to tungsten layer chemical-mechanical polishing solutions specifically adapted for chemical-mechanical polishing with fixed abrasive pads. In one implementation, a semiconductor wafer having a layer comprising tungsten at greater than or equal to 50% molar is provided. Such is positioned in proximity with a fixed abrasive chemical-mechanical polishing pad. A tungsten layer chemical-mechanical polishing solution is provided intermediate the wafer and pad. The solution comprises a tungsten oxidizing component present at from about 0.5% to 15% by volume and a pH of less than or equal to about 6.0. The tungsten comprising layer is chemical-mechanical polished with the fixed abrasive pad with the tungsten layer chemical-mechanical polishing solution being received between the wafer and the pad. In one implementation, tungsten from the layer is oxidized with a solution comprising a tungsten oxidizing component present at from about 0.5% to 15% by volume and a pH of less than or equal to about 6.0. One or both of tungsten and tungsten oxide is then polished from the tungsten comprising layer with a fixed abrasive chemical-mechanical polishing pad. In one implementation, the invention comprises a tungsten layer chemical-mechanical polishing solution.

Electroplating of High Tungsten Content Ni / W Alloys

Abstract: Induced codeposition of tungsten with nickel from aqueous solutions of sodium tungstate was studied. Ammonia is commonly added to such plating baths to adjust the pH, but its role as a ligand for nickel complexes is usually ignored. Removing ammonia helped to increase the tungsten content of the alloy to 50 atom % (76 wt %). First indications for the formation of an amorphou s Ni/W alloy at intermediate concentrations of tungsten (20-40 atom %) were observed. It is shown that the reported effect of tem perature on the composition of the alloy is due to the removal of ammonia from solution. In its absence, the tungsten content of the alloy plated from a given solution is essentially independent of temperature. © 2000 The Electrochemical Society. S1099-0062(00)07-098-X. All rights reserved.

Quantitative adhesion measures of multilayer films: Part II. Indentation of W/Cu, W/W, Cr/W

Abstract: Sputtered copper and tungsten thin films both with and without tungsten and chromium superlayers were tested by using nanoindentation probing to initiate and drive delamination. The adhesion energies of the films were calculated from the induced delaminations using the analysis presented in “Quantitative adhesion measures of multilayer films: Part I. Indentation mechanics.” Copper films ranging in thickness from 150 to 1500 nm in the as-sputtered condition had measured adhesion energies ranging from 0.2 to 2 J/m2, commensurate with the thermodynamic work of adhesion. Tungsten films ranging in thickness from 500 to 1000 nm in the as-sputtered condition had measured adhesion energies ranging from 5 to 15 J/m2. The superlayer was shown to induce radial cracking when under residual tension, resulting in underestimation of the adhesion energy when the film was well adhered. Under conditions of weak adherence or residual compression, the superlayer provided an excellent means to induce a delamination and allowed an accurate and reasonably precise quantitative measure of thin film adhesion.

A Supramolecular Tetra‐Keggin Polyoxometalate [Nb4O6(α‐Nb3SiW9O40)4]20−

Abstract: Giant polyoxometalates with catalytic, magnetic, and antiviral properties, which are in part attributable to their structures, are currently of great interest. Herein is described the synthesis and characterization of 1, a structurally novel tetrameric complex from Keggin ions (see picture). This complex is stable under the physiological conditions of the stomach (pH 1-2), which is interesting since related keggin anions are among the least toxic and yet most potent antiviral agents of the more than 300 polyoxometalates investigated biologically and pharmacologically.

Tin contact barc for tungsten polished contacts

Abstract: The present invention provides improved critical dimension control on oxide films using a titanium nitride (TiN) antireflection coating (ARC). The present invention also provides for improved methods for forming more uniform local interconnects and contact holes through oxide films, by providing a TiN layer as an ARC layer. The TiN ARC layer is used in a process for etching contacts and filling the contacts with a barrier metal made out of Ti or TiN and a tungsten fill. The TiN layer is easily removed during a tungsten polish, which also removes the barrier metal. Additionally, the TiN can serve as a hardmask for the contact etch, since the chemistry is typically selective to TiN. This allows the resist to be thinned down, providing the lithography process with a larger process window.

Nitride compound semiconductor light emitting element and its manufacturing method

Abstract: A nitride compound semiconductor light emitting element is made by stacking a metal layer made of one of elements: palladium (Pd), scandium (Sc), vanadium (V), zirconium (Zr), hafnium (Hf), tantalum (Ta), rhodium (Rh), iridium (Ir), cobalt (Co) and copper (Cu), and another metal layer made of one of elements: titanium (Ti), nickel (Ni), molybdenum (Mo), tungsten (W) and magnesium (Mg), to increase the adhesive strength of its electrodes with a semiconductor layer, reduce the contact resistance of the electrodes to improve the ohmic characteristics, and improve the external quantum efficiency by combination of thin-film metals with a transparent electrode.

Synthesis, characterization, and catalytic testing of W-MCM-41 mesoporous molecular sieves

Abstract: A novel tungsten-containing MCM-41 mesoporous molecular sieve was synthesized by the hydrolysis of tetraethylorthosilicate and ammonium tungstate in the presence of cetylpyridinium bromide as template in strongly acidic medium. Physicochemical characterizations of this composite performed by means of powder X-ray diffraction, ICP atomic emission, FT-IR, laser Raman, and diffuse reflectance UV–Vis spectroscopy verified that tungsten ion could be isolated in framework positions of the MCM-41 mesostructure by this approach. Thermo-gravimetric study on this composite suggested that above 90% of the template encapsulated in the as-synthesized mesophase was recoverable by direct ethanol extraction. A catalytic test using hydrogen peroxide hydroxylation of cyclohexene as probe reaction proved that the framework tungsten site in the W-MCM-41 could afford the mesophase with fairly high activity in promoting this reaction, wherein acetic acid was found to be useful as solvent.

Heterogeneous recombination of atomic bromine and fluorine

Abstract: Recombination coefficients (γ) of Br and F atoms have been measured for crystalline Si, quartz, photoresist, anodized aluminum, poly-Si, WSix, tungsten and stainless steel surfaces for a range of temperatures. The γBr and γF values are compared to our previously reported measurements of γCl [G. P. Kota, J. W. Coburn, and D. B. Graves, J. Vac. Sci. Technol. A 16, 270 (1998)]. In general, the Br-, Cl- and F-atom recombination coefficients decrease as the surface temperature increases. The γBr values are similar to the γCl values for the various surfaces. At room temperature, γBr is highest (>0.4) for stainless steel and tungsten, moderate (0.1–0.4) for poly-Si, WSix and anodized Al, and lowest (<0.05) for c-Si, quartz and photoresist. However, γF, at room temperature, is no greater than 0.05 for all the surfaces. γF increases slightly as the temperature is decreased to 80 K but is still below 0.1 for all the surfaces. The recombination coefficient data as a function of temperature for all surfaces are fit t...

Use of magnetic arc oscillation for grain refinement of gas tungsten arc welds in α–β titanium alloys

Abstract: In an effort to refine the weld metal grain structure in α–β titanium alloys, gas tungsten arc welding was carried out, during which transverse oscillations of the arc were induced through the use of an alternating external magnetic field. At optimum values of oscillation amplitude and frequency in both the alloys investigated, considerable refinement of the fusion zone grain structure was achieved. This could be attributed to factors that include enhanced fluid flow, reduced temperature gradients, and a continually changing weld pool size and shape owing to the action of the imposed magnetic field. The reduction in the prior β grain size was shown to result in a notable increase in fusion zone tensile ductility. Post-weld annealing increased ductility in all cases, but the magnetically treated material continued to show a higher elongation than that of the untreated material even after post-weld heat treatment.

Low-temperature crystallization of amorphous silicon using atomic hydrogen generated by catalytic reaction on heated tungsten

Abstract: A method for crystallizing amorphous silicon (a-Si) films at low temperatures is proposed. In the method, a-Si films are crystallized at temperatures lower than 400 °C by annealing in the presence of atomic hydrogen. The hydrogen atoms are generated by catalytic cracking reaction of H2 gas on a heated tungsten catalyzer in the catalytic chemical vapor deposition apparatus. It is found that the crystalline fraction of such an a-Si film is increased from 0% to several tens %, and at the same time the a-Si film itself is etched with the rate of several tens nm/min by annealing in atomic hydrogen. This increment of crystalline fraction appears dependent on the quality of initial a-Si films. It is implied that there are several types of a-Si even if the difference among a-Si films cannot be detected by Raman scattering spectroscopy and other means for measurements.

Tungsten coating for improved wear resistance and reliability of microelectromechanical devices

Abstract: A process is disclosed whereby a 5-50-nanometer-thick conformal tungsten coating can be formed over exposed semiconductor surfaces (e.g. silicon, germanium or silicon carbide) within a microelectromechanical (MEM) device for improved wear resistance and reliability. The tungsten coating is formed after cleaning the semiconductor surfaces to remove any organic material and oxide film from the surface. A final in situ cleaning step is performed by heating a substrate containing the MEM device to a temperature in the range of 200-600 ° C. in the presence of gaseous nitrogen trifluoride (NF 3 ). The tungsten coating can then be formed by a chemical reaction between the semiconductor surfaces and tungsten hexafluoride (WF 6 ) at an elevated temperature, preferably about 450° C. The tungsten deposition process is self-limiting and covers all exposed semiconductor surfaces including surfaces in close contact. The present invention can be applied to many different types of MEM devices including microrelays, micromirrors and microengines. Additionally, the tungsten wear-resistant coating of the present invention can be used to enhance the hardness, wear resistance, electrical conductivity, optical reflectivity and chemical inertness of one or more semiconductor surfaces within a MEM device.

Surface oxide debonding in field assisted powder sintering

Abstract: Field activated sintering techniques (FAST) have been applied to two high-temperature powder materials: tungsten and NiAl. High and atomic resolution electron microscopy (HREM/ARM) of tungsten powder sintered via FAST showed essentially clean boundaries. Analytical transmission electron microscopy (TEM) of FAST sintered NiAl also showed boundaries free of surface oxide layer(s). However, small alumina precipitates were found at and near prior particle (grain) boundaries. The boundary cleaning and precipitation phenomena are manifestations of an applied pulsed electric field.