Silicon Tungsten Research Articles

The oxidation behaviour of mixed tungsten silicon sputtered coatings

W-Si-N coatings were deposited by sputtering and their chemical composition, structure, thermal and oxidation behaviour were characterised. Si-containing films are essentially amorphous. W 69Si 31 film crystallises at 750 °C as α-W and W 5Si 3 phases whereas no significant structural transformations were observed for W 24Si 21N 55 film up to 1000 °C, In both cases elemental diffusion (Si and N) for the substrate was detected after thermal annealing. These coatings present much better oxidation resistance than W and W 45N 55 coatings.

Copper Damascene Interconnection with Tungsten Silicon Nitride Diffusion Barrier Formed by Electron Cyclotron Resonance Plasma Nitridation

This paper describes the application of tungsten silicon nitride (WSiN) formed by electron cyclotron nitridation (ECR) plasma nitridation as a diffusion barrier for copper (Cu) damascene interconnection. WSiN(6 nm)/WSix(14 nm) multi-layer prevents Cu diffusion well when WSiN is formed with RF bias application to the substrate. The RF power increases the nitrogen concentration of the WSiN and enhances its amorphousness, which lead to the improved barrier capability. WSiN can be formed inside the trench, and the WSiN on the trench side walls prevents Cu diffusion. The use of this extremely thin barrier metal suppresses the increase of interconnection resistivity.

Formation process of mixed silicon and tungsten carbide from copyrolysis of polysilane and metallic tungsten: Part I

Copyrolysis of polysilane with metallic tungsten addition in the range of 0–12 at % W was performed. A significant decrease of the mass loss during the polysilane pyrolysis was observed. Also the specific surface area, gas evolution and occuring phase formation changed. The tungsten forms silicides and carbides depending on the applied pyrolysis temperature. The reactions are controlled by transport phenomena of carbon and tungsten. In the end of the process the silicon carbide (SiC) and tungsten carbide (WC) are stable. The obtained powders are sintered to porous ceramics with a significant pore gradient and a variation of the hardness in a micrometer range.

Investigation of the nature of low-frequency fluctuations of the field emission current using a two-dimensional distribution function

A two-dimensional distribution function in the frequency range 0.03–1 Hz was used to investigate the statistical characteristics of the fluctuations of the field emission current from single crystals of tungsten and p-type silicon. In order to determine the type of nonlinearity predominating in the low-frequency noise of the emission current, calculations were made of the two-dimensional distribution function for a Gaussian random process subjected to a given type of nonlinear transformation and the profiles of the experimental two-dimensional distribution functions were compared with dependences obtained by numerical methods. It was established that fluctuations of the effective emitting surface of the cathode, the barrier transmission, the work function, and of the electric field strength near the emitter surface may act as primary sources of low-frequency noise in the field emission current.

Diffusion Barrier Mechanism of Extremely Thin Tungsten Silicon Nitride Film Formed by ECR Plasma Nitridation

The diffusion barrier mechanism of tungsten silicon nitride (WSiN) film formed by ECR plasma nitridation is investigated. For this purpose, we examined film thickness, nitrogen content, surface composition, and local atomic ordering of this WSiN and correlated these characteristics with its barrier capability. It is revealed that WSiN shows good barrier capability when RF bias is applied to the substrate during nitridation even though it is less than 6-nm thick. Applying RF bias increases the nitrogen content in WSiN. Moreover, Si atoms are preferentially sputtered and the local atomic ordering in WSiN is lowered because the effect of ion bombardment is remarkably pronounced. It is supposed that these film characteristics contribute to the suppression of phosphorus diffusion through interstitial sites. As a result, WSiN functions as an excellent barrier layer even though it is extremely thin.

Improvement of Machinability of Sintered Composite-type Alloyed Steel Powder

Composite-type alloyed steel powder has drawn great attention in recent years due to the rapid increase of high strength materials. A typical powder consisting of iron with nickel and molybdenum as an additive which adheres to the surface of iron particles is used. This type of sintered alloyed steel causes excessive tool wear. The purpose of this study is to improve the machinability of the sintered alloyed steel by adding nonmetallic materials. Experiments show that the addition of 3% glass to the sintered alloyed steel increases the tool life 100 times. In order to clarify the mechanisms of the increase of tool life, the worn face of the cutting tool is examined by an Electron Probe Microanalyzer (EPMA). The analysis shows that the glass additive acts as a protective film and lubricant when cutting with silicon nitride and tungsten carbide tools, respectively.

A Comparative Study of Residual Stresses in Single and Multilayer Composite Diamond Coatings

ABSTRACTResidual stresses in four types of diamond films deposited by hot filament chemical vapor deposition on molybdenum substrate, three types on tungsten carbide or silicon nitride substrate are measured. Residual stresses are determined by X-ray method and Raman spectroscopy. The results from both these techniques are compared and conclusions are made on the mechanisms of adhesion of diamond films to the different substrates.

A WSix N Diffusion Barrier Formed with Electron Cyclotron Resonance Nitrogen Plasma

The effectiveness of using a tungsten silicon nitride layer as a dopant diffusion barrier is investigated. The layer can be formed by simple surface nitridation using electron cyclotron resonance (ECR) plasma of nitrogen gas without substrate heating. Structural analysis reveals that the layer is very thin (5.0 to 6.0 nm) and that it remains intact and has an amorphous structure free from grain boundaries even after annealing at 850°C. The layer formed with ECR nitrogen plasma is found to act as an excellent barrier to dopant diffusion.

Nitrogen-rich carbon nitride film formation by means of ion beam and vapor deposition method

Abstract Carbon nitride films with 1 μm thickness were prepared on tungsten carbide (WC) and silicon wafers by Ion Beam and Vapor Deposition (IVD). Films with a composition ratio CR(C/N) = 0.5∼0.7 on WC prepared by nitrogen ions with energies lower than 800 eV showed a hardness of 6500 kgf/mm2 which is comparable or greater than that of diamond. The structure of the films is amorphous. For the hardest films, it is considered that all nitrogen atoms are covalently bond to carbon atoms.

A cellular automaton to filter events in a high energy physics discrete calorimeter

In this paper the noise-filtering capabilities of a cellular automaton are studied. The tests have been performed on 4 GeV pion experimental events taken with a Silicon Tungsten tracking calorimeter at CERN PS. Particle interaction with the material of the calorimeter can produce straight tracks or hadronic showers. The evolution rules devised for the CA have therefore to reckon with these different topologies in order to remove noise and restore interrupted tracks. At the same time, strips hit by particles should be affected as little as possible. The distributions of some discriminating parameters are compared with Monte Carlo data before and after being filtered by the automaton and the agreement is shown to improve. The Cellular Automaton constitutes a simple (Boolean logic) and fast (with possible on-line applications) filter. Its applications range from particle discrimination to track restoration in time-worn detectors.

Soft-x-ray multilayer mirrors with laterally varying film thicknesses fabricated using laser-beam-scanning chemical vapor deposition

The authors have developed a control method of spatial film thickness distribution of multilayer mirrors for soft-x-ray focusing systems using an argon–fluoride (ArF) excimer laser-induced chemical vapor deposition (LCVD). A line-shaped laser beam is unidirectionally scanned over an area of 100×100 mm2. The scanning speed is controlled in response to a film thickness distribution which is required to be obtained. A tungsten–silicon (W/Si) multilayer with laterally varying film thickness is successfully fabricated on the design rule, and soft-x-ray (λ=12.8 nm; not polarized) reflectivities from 37% to 20% are obtained at the grazing angles from 18° to 22° in response to the film thickness distribution. Furthermore, the amount of the soft x rays reflected by the multilayer within 100 mm of the substrate is estimated at about 90% of that in the case of the designed distribution, and the feasibility of LCVD for fabricating multilayer mirrors for high performance soft-x-ray focusing systems has been demonstrated.

TEM examination of wear debris from a self-lubricating metal-matrix composite prepared by ultramicrotomy

Self-lubricating materials are usually multi-phase composites comprising of a solid lubricant dispersed in a matrix of a metal or a polymer. During sliding contact, chemical reactions among the constituent phases of the composite, the counterface and the gases in the surrounding environment are inevitable. The wear debris is a product of such chemical (or tribochemical) reactions. Determination of the chemistry and the crystal structure of the wear debris is therefore crucial to the understanding of the wear mechanisms. In self-lubricating composites, the quantity of the debris generated is often too small to perform x-ray diffraction.It has been previously demonstrated that self-lubricating aluminum metal-matrix composites can be synthesized by dispersing silicon carbide and tungsten disulfide particles in commercial aluminum alloy matrices. A typical microstructure of an Al-0.10SiC-0.05WS2 MMC is shown in Fig. 1. The friction and wear test was performed, in a ball-on-disk configuration, on a polished disk of the aluminum MMC against a 440C steel ball.

Neural networks with stochastic preprocessing for particle recognition in cosmic ray experiments

Neural networks can be used with good results in particle recognition. An application on 4 GeV CERN experimental data of e− and π−, taken with the prototype of the silicon tungsten calorimeter of the WIZARD collaboration, is shown. The full detector is being used for cosmic ray antimatter research. A stochastic preprocessing is used in connection with a neural network (back propagation algorithm). This preprocessing consists in giving as input to the net the probability, for a given discriminating parameter value, to belong to a given particle class. In this way the input layer is normalized and the back propagation algorithm can exploit the relations between different parameters. This results in an increased convergence speed and recognition capability of the net. With this algorithm a high hadron (π−) recognition efficiency (93.6% on experimental data, 97.1% on Monte Carlo data) and a low electromagnetic contamination (0.1% on experimental data and, 3 × 10−4 on Monte Carlo) is reached.

The mechanical Properties of CVD Diamond Films, and Diamond Coated Fibres and Wires

ABSTRACTTwo areas of thin film property measurement are addressed. The first is that of flat films, either on a substrate or free-standing. The film properties only are of interest. Therefore, when the film remains attached to a substrate during testing, an appropriate analysis is used to subtract the effect of the substrate. The films under test are prospective protective coatings and ‘window’ materials for infrared applications, namely CVD diamond (Hot filament Assisted, HFACVD and Microwave plasma assisted, MPACVD) and Germanium carbide (Ge:C). The mechanical properties under investigation are the Young's modulus and the internal film stress.In the second case the substrates are small diameter fibres and wires coated with CVD diamond. The mechanical properties measured were composite, containing contributions from both the substrate and the film. These coated fibres and wires, have possible applications as reinforcement phases in the production of composites. They are silicon carbide (SiC) and Tungsten (W) of diameters varying between 10 and 125μm. A technique has been developed to measure the Young's modulus of individual coated fibres.

Effects of Nitrogen on Formation and Properties of Diamondlike Films Synthesized by Dual Ion Beam Deposition

ABSTRACTDiamondlike carbon-nitrogen films on silicon (111) wafer and tungsten carbide plates have been prepared by using dual ion beam sputtering deposition and simultaneous bombardment by N+ with energies of 100-800 eV at room temperature. These films retain their diamondlike characteristics. However, as the nitrogen content increases from 10% at to 20% at., the Auger electron spectroscopy spectra of films change obviously in fine structure and the main Cls peak of carbon atoms in the X-ray photoelectron spectroscopy spectra shifts to 285.65 eV. The maximum hardness of these films on tungsten carbide plates is about 5260 kg/mm2. The films have an amorphous structure and smooth surface. The state of nitrogen in films and its influence on the structure and properties of films are discussed.

Mechanism of Diamond Growth on Carbide Substrates Using Fluorocarbon Gases

ABSTRACTThe etching and growth behavior of diamond in CxFy / O2 / H2 plasmas have been investigated. Using this gas Mixture, diamond can nucleate on untreated tungsten carbide and silicon carbide substrates up to a density of 108 crystallites/cm2. This compares to a density of 102 crystallites/cm2 when using a methane gas mixture and these same substrates. The increase in nucleation density is attributed to the selective etching of the non-carbon component of the carbide with subsequent nucleation on the carbon enriched surface. The effect of temperature on the nucleation rate has been studied with a lower nucleation density at higher growth temperatures.

Lubricationless blowers for transfer gas pumps

The main element of the sealing system is the sealing unit situated in housing i; it consists of two identical stages and includes the graphite ring 2 with the rubber sealing ring 4 with circular cross section which is pressed by springs 3 against the ring 5 that is made of tungsten carbide, titanium carbide, or silicon carbide. With the aid of sleeve 6 and pins 7 ring 5 is fastened to the shaft and rotates together with it. Ring 9 serves for making the joint between sleeve 6 and ring 5 air-tight. The bracelet spring 10 ensures self-centering of ring 5 relative to sleeve 6.

JESSOP JS ALLOY 276

Abstract JESSOP JS Alloy 276 is a nickel-chromium alloy with high molybdenum and moderate tungsten but low iron and silicon contents. This composition provides superior corrosion resistance to a wide variety of environments. It has found wide acceptance in the chemical and petrochemical process industry, flue gas desulfurization systems and the pulp and paper industries. This datasheet provides information on composition, physical properties, elasticity, and tensile properties. It also includes information on high temperature performance and corrosion resistance as well as heat treating, machining, and joining. Filing Code: Ni-330. Producer or source: Jessop Steel Company. Originally published March 1986, revised April 1988.

Photoassisted reduction of sulfur dioxide in nonaqueous solutions at p-type semiconductor electrodes

The electrochemical behavior of SO/sub 2/ has been investigated at illuminated (632.8 and 514.5 nm) p-type semiconducting silicon (Si) tungsten sulfide (WS/sub 2/), and indium phosphide (InP) in (tetra-n-butyl ammonium perchlorate n-Bu/sub 4/N)C1O/sub 4/ solutions. SO/sub 2/ is photoreducible at each of these materials to form S/sub 2/O/sub 4//sup 2 -/, but the electrical power savings efficiencies are variable. The best power savings efficiency, approx. 11% at 514.5 nm (100 mW/cm/sup 2/), is obtained with a p-type InP photocathode modified by photoelectrodeposition of approx. 5 x 10/sup -8/ mol/cm/sup 2/ of Pt onto the surface. Naked p-InP is considerably less efficient, owing to poor kinetics for the reduction of SO/sub 2/. The deposition of platinum (Pt) onto p-InP forms neither a uniform ohmic contract nor a Schottky barrier; rather, studies of platinized n-InP show directly that the Pt serves as a catalyst for SO/sub 2/ reduction. Power savings efficiencies for p-type WS/sub 2/ and textured Si are low, owing to small output voltages. Preparative, controlled-potential photoelectrochemical reduction of SO/sub 2/ at all three photoelectrodes and Pt in CH/sub 3/CN/0.1 M SO/sub 2//0.5 M (n-Bu/sub 4/N)ClO/sub 4/ has been demonstrated to give > 90% current efficiency for formation of S/sub 2/O/submore » 4//sup 2 -/, which can be precipitated and collected as Na/sub 2/S/sub 2/O/sub 4/.« less

Amorphous Thin Film Diffusion Barriers on GaAs and InP

Thin film amorphous W-Si and TiW-Si diffusion barriers have been studied on GaAs and InP surfaces for the purpose of establishing their reliability for ohmic contacts and Schottky barriers, particularly under high temperature stress. The amorphous films were formed by a new method in which alternate layers of tungsten or TiW and silicon were sputter deposited to a total thickness of about 1300 Å and subsequently annealed near the glass transition temperature Tg(≈ 500 °C). Electron channeling and reflection electron diffraction were used to determine the amorphous nature of the films as deposited and after 4 h anneals near Tg. The as-deposited films had interfacial amorphous regions with compositions determined by interfacial reactions during the sputtering process. As-deposited W-Si films showed a weak channeling pattern which came from the unreacted polycrystalline tungsten layers. From Auger electron spectroscopy (AES) sputter profiles, it was concluded that the amorphous regions were at the W-Si interfaces which had the required tungsten-to-silicon composition ratio. After annealing at 500 °C for 4 h, the films were completely amorphous with no marked evidence of crystallization, indicating interfacial reactions extended completely into the tungsten layers. High magnification scanning electron microscopy (by a factor of 20 000) examination of the films after annealing revealed smooth and continuous surfaces with no evidence of grain boundaries. Diffusion along grain boundaries between gold and GaAs or InP in these amorphous thin films was thus almost completely eliminated. Interdiffusion of gold in layered structures (e.g. Au/(W–Si)/GaAs) was studied by AES sputter profiling techniques. No interdiffusion of gold or GaAs was observed after 16 h anneals at 400 °C. With Au/(W-Si)/InP structures, no interdiffusion was observed after 8 h anneals at 450 °C. These results are significant improvements over those for previous polycrystalline diffusion barriers (e.g. TiPt) which degrade after 1 h at 350 °C. Based on the AES sputter profiles, the diffusion coefficients in W-Si amorphous thin films were found to be less than 3 × 10−18 cm2 s−1 at 400 °C for gold, gallium and arsenic and less than 6 × 1018 cm2 s−1 at 450 °C for gold, indium and phosphorus.