- Tungsten Disilicide (WSi2): Synthesis, Characterization, and Prediction of New Crystal Structures
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Transition metal silicides have attracted great attention due to their potential applications in microelectronics, ceramics, and the aerospace industry. In this study, experimental and theoretical investigations of tungsten based silicides were performed.
- Lukovi?, Jelena,Zagorac, Dejan,Sch?n, J. Christian,Zagorac, Jelena,Jordanov, Dragana,Volkov-Husovi?, Tatjana,Matovi?, Branko
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- PROPERTIES OF CHEMICAL VAPOR DEPOSITED TUNGSTEN SILICIDE FILMS USING REACTION OF WF6 AND Si2H6.
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Tungsten silicide films were formed by the chemical vapor deposition method using the reaction WF//6 and Si//2H//6. The deposition rate, resistivity, composition, stress, crystal structure, and content of impurities were studied and compared with tungsten silicide films deposited by reaction of WF//6 and SiH//4. The tungsten silicide films made using Si//2H//6 have a higher deposition rate and higher Si concentration than those made by using SiH//4 at the same substrate temperature. For these reasons, the tungsten silicide films made by using Si//2H//6 were found to have a resistivity that is a little higher and, after annealing, a stress that is smaller than that made by SiH//4. Also, the resistance of tungsten silicide to peeling is larger than that of the film made by using SiH//4.
- Shioya,Ikegami,Kobayashi,Maeda
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- Composition of tungsten silicide films deposited by dichlorosilane reduction of tungsten hexafluoride
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The composition profile of tungsten silicide (WSix) films deposited by low-pressure chemical vapor deposition employing dichlorosilane (DCS) reduction of tungsten hexafluoride (WF6) is studied. Diffusion is the reaction rate-limiting process at chuck temperatures above 550°C and uniform in-depth composition profiles can be obtained. Below 550°C, however, the in-depth composition profile is not uniform for the surface reaction rate-limiting process. Tungsten-rich layers with a Si composition, x, of 1.5, are initially deposited due to the reduction of WF6 by the Si surface. This layer is amorphous or microcrystalline. Thereafter, the silicon content of the film increases with increasing thickness and a uniform composition profile is obtained as determined by the DCS/WF6 flow rate ratio in the chemical reaction. Chemical vapor-deposited tungsten silicide (WSix) films have been extensively used as polycide gate and interconnections for very large-scale integrated circuits.
- Hara,Miyamoto,Hagiwara,Bromley,Harshbarger
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- CHANGES IN RESISTIVITY AND COMPOSITION OF CHEMICAL VAPOR DEPOSITED TUNGSTEN SILICIDE FILMS BY ANNEALING.
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Chemical vapor deposited (CVD) tungsten silicide films were formed by a cold wall reactor. These films were annealed in N//2 to investigate changes in resistivity, composition, thickness, and impurity. The change in resistivity after 1000 degree C annealing becomes larger as the film reaches the stoichiometric value. A composition change occurs in a film whose composition Si/W is more than 2. 6. Excess Si in the WSi//x films (x greater than 2. 6) is segregated in the boundary between WSi//x and poly-Si. A thickness change of about 15% occurs after 1000 degree C annealing at WSi//2//. //4 on SiO//2; this value is smaller than the calculated value. F and H, which are impurities in WSi//x films decrease gradually and diffuse into gate SiO//2 after 1000 degree C annealing.
- Shioya,Itoh,Kobayashi,Maeda
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- Dense WSi2 and WSi2-20 vol.% ZrO2 composite synthesized by pressure-assisted field-activated combustion
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The simultaneous synthesis and consolidation of WSi2 and WSi2-20 vol.% ZrO2 from elemental powders of W, Si, and ZrO2 additive was investigated. The synthesis was carried out under the combined effect of an electric field and uniaxial pressure. The final density of the products increased nearly linearly with the applied pressure in the range 10 to 60 MPa. Highly dense WSi2 and WSi2-20 vol.% ZrO2 with relative densities of up to 98.0% were produced with the application of a 60 MPa pressure and a 3000 A DC current. The percentages of the total shrinkage occurring before and during the synthesis reaction were 17.5 and 82.5% for the case of WSi2, and 25.8 and 74.2% for the case of WSi2-20 vol.% ZrO2, respectively. The respective Vickers microhardness values for these materials were 8.2 and 10.6 GPa. From indentation crack measurements, the fracture toughness values for WSi2 and WSi2-20 vol.% ZrO2 were calculated to be 3.2 and 9.4 MPa m1/2, respectively.
- Shon,Rho,Kim,Munir
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- Chemical reactions, anisotropic grain growth and sintering mechanisms of self-reinforced ZrB2-SiC doped with WC
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Transmission electron microscopy study of pressureless sintered ZrB 2-20 vol% SiC composites with WC (5-10 vol%) additions was carried out in this work. Two independent chemical reactions in which the ZrO 2 impurities were removed from ZrB2 grain surface were confirmed. Three new formed phases, (W, Zr)ssB, (Zr, W) ssC, and (W, Zr)ssSi2, apart from the plate-like ZrB2 and SiC grains, were identified in the samples. Microstructure observations strongly suggest that the liquid phases in terms of (W, Zr)ssB and (W, Zr)ssSi2, appear in this system during the sintering process below 2200°C, and the former could well wet the ZrB2 grain boundaries. The mass transport process between ZrB2 and (W, Zr)ssB was also confirmed by scanning-transmission electron microscope analysis. The above results supports that the densification at 2200°C is assisted by liquid phase and the elongation of ZrB2 platelets resulted from the Ostwald ripening during the dissolution-diffusion-precipitation process.
- Zou, Ji,Sun, Shi-Kuan,Zhang, Guo-Jun,Kan, Yan-Mei,Wang, Pei-Ling,Ohji, Tatsuki
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- WSix FORMATION IN W-Si MULTILAYERS.
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The formation of WSi//x phases from multiple thin layers of W and Si was investigated. Tungsten and silicon thin films of approximately 5 nm thickness were deposited sequentially onto GaAs substrates by dc magnetron sputtering from elemental targets. The total film thickness was approximately 300 nm. The multilayered structure was subjected to rapid thermal annealing at 900 degree C. The extent of the reaction, the grain size, and the crystal structure of the silicides were determined using transmission electron microscopy and X-ray diffraction. Schottky contacts were of good quality for x less than equivalent to 0. 52, with a barrier height ( PHI ) of 0. 7 V and an ideality factor (n) of 1. 15. Schottky contacts with higher silicon concentrations were poor. The WSi//x (x equals 0. 52) Schottky contact has been successfully incorporated into a self-aligned-gate field-effect transistor.
- Eicher,Bruce
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- In situ barrier formation using rapid thermal annealing of a tungsten nitride/polycrystalline silicon structure
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This letter describes the use of rapid thermal annealing (RTA) to form a barrier layer applicable to the gate electrode in dynamic random access memory devices with a stacked structure [tungsten nitride (WNx)/polycrystalline Si (poly-Si)]. After RTA, the reactively sputtered amorphous WNx film on the poly-Si was transformed to a low-resistive α-phase W and nitrogen-segregated layer. Most of the nitrogen in the WNx film was dissipated and a relatively small amount of the nitrogen was segregated at the interface of the α-phase W and poly-Si. The segregated layer was estimated to be 2 nm thick and revealed a silicon nitride (Si-N) bonding status. More importantly, we found that this thin segregated layer successfully protected the formation of tungsten silicide, even after RTA at 1000°C for 2 min in a hydrogen environment.
- Lee, Byung Hak,Lee, Kee Sun,Sohn, Dong Kyun,Byun, Jeong Soo,Han, Chang Hee,Park, Ji-Soo,Han, Sang Beom,Park, Jin Woon
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- High frequency induction heated synthesis and consolidation of nanostructured TaSi2-WSi2 composite
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A dense nanostructured TaSi2-WSi2 composite was simultaneously synthesized and sintered by the high frequency induction heating method within 2 minutes from mechanically activated powder of Ta, W and Si. A highly-dense TaSi2-WSi2 composite was produced under simultaneous application of a 80 MPa pressure and the induced current. The mechanical properties and microstructure were investigated.
- Shon, In-Jin,Kang, Hyun-Su
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- Tungsten silicide films deposited by SiH2Cl2-WF6 chemical reaction
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This paper studies tungsten silicide films deposited by the SiH2Cl2 (DCS)-WF6 chemical reaction. The deposition rat was held at around 1500 angstrom/min at temperatures above 500°C. However, the deposition rate decreased r
- Hara,Miyamoto,Yokoyama
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- Determination of the standard free energies of formation for tungsten silicides by EMF measurements using lithium silicate liquid electrolyte
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EMF measurements on silicon concentration cell were carried out using lithium silicate electrolyte in the temperature range 1300-1500 K. Using the EMF-temperature relations obtained, the standard free energies of formation for W5Si3 and WSi2 have been calculated as functions of temperature: ΔG0(W5Si3) (kJ mol-1) = -128.6 - 0.0132 (T (K)) ± 0.42 and ΔG 0(WSi2) (kJ mol-1) = -98.5 + 0.0095 (T (K)) ± 0.15, respectively. Combining the results with thermodynamic data, the standard enthalpies of formation for silicides at 298 K have been obtained as ΔH0(W5Si3, 298) (kJ mol-1) = -133 ± 25 and ΔH0(WSi2, 298) (kJ mol -1) = -82 ± 6, respectively. A new eutectoid reaction W 5Si3 ? W + WSi2 occurring around 700 K is suggested in W-Si binary system. Published by Elsevier B.V.
- Fujiwara, Hiroyasu,Ueda, Yukitomi,Awasthi, Alok,Krishnamurthy, Nagaiyar,Garg, Sheo Parkash
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- LPCVD WSi2 films using tungsten chlorides and silane
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This paper makes a systematic study of blanket and selective low pressure chemical vapor deposition (LPCVD) WSi2 films from tungsten chlorides, silane, hydrogen, and argon on silicon as well as on patterned oxidized silicon substrates. Experiments were performed by varying the initial gaseous WCl4 to SiH4 ratio (Rx) or the deposition temperature (Td). Initially, yield and CVD-phase diagrams of the W-Si-Cl-H-Ar chemical system were drawn, based on thermodynamic simulations. The deposition of pure WSi2 phase and mixed solid phases involving W, W5Si3, WSi2, and Si was predicted to occur in relation to process parameters. The corresponding films were grown in a cold-wall reactor and characterized by x-ray diffraction, scanning electron microscopy, four-point probe, and Auger electron spectroscopy studies. Good agreement was found between experimentally observed solid phases and thermodynamically simulated results, under the same conditions. The growth rate of films for an Rx value varying between 0.3 and 1.0 at 873 K reaches a maximum at Rx = 0.5. The Arrhenius plot of films grown between 773 and 1073 K shows a linear increase in growth rate up to 923 K, followed by saturation at high temperatures. Films processed above 823 K have a smooth surface and interface, indicating that the chloride-based chemistry does not affect the silicon substrate even at high temperatures. Based on the above mentioned studies, a set of process parameters was defined, and selective LPCVD WSi2 films were deposited on fine-patterned oxidized silicon.
- Thomas,Suryanarayana,Blanquet,Vahlas,Madar,Bernard
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- (Mo,W)5Si3-(Mo,W)Si2 eutectics: Properties and application in composite materials
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Experimental data are presented on (Mo,W)5Si3 and (Mo,W)Si2 solid solutions and are analyzed using the known phase diagrams of the binary systems Mo-Si and W-Si. It is shown that, with increasing tungsten content, the melting temperature of the (Mo,W)5Si 3-(Mo,W)Si2 eutectic rises. Surprisingly, the alloys with W:Mo atomic ratios close to unity are found to contain, along with the suicide solid solutions, molybdenum disilicide almost free of tungsten. The mean room-temperature hardness of the eutectic alloys varies nonmonotonically with tungsten content and shows maxima at ?33 and ?75 at. % W. The surface texture is found to have a significant effect on the rate of high-temperature gas corrosion. The possibility of compositional control (variations in the W:Mo and (Mo,W)5Si3:(Mo,W)Si2 ratios) over the thermal expansion of the alloys is analyzed. Data are presented on the temperature-dependent resistivity of SiC-matrix composites.
- Gnesin,Gurzhiyants,Borisenko
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- Tungsten thin-film deposition on a silicon wafer: The formation of silicides at W-Si interface
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The interphase boundary formed in the process of tungsten thin-film deposition on a silicon wafer is investigated. These films are produced via (1) a CVD technique relying on hydrogen reduction of tungsten hexafluoride, (2) the same technique supplemented
- Plyushcheva,Mikhailov,Shabel'nikov,Shapoval
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- Preparation, characterization, and properties of various novel ionic derivatives of pentacarbonyltungsten
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The complexes [Li(DIME)2][W(CO)5L] [L = OCN 2, NCS 3a, PPh2 4, SiMe2Ph 8, N(SiMe3)2 9, CH2Ph 10, Si6Me11 11; DIME = diethylene glycol dimethyl ether] have been prepared by reaction of [Li(DIME)2][W(CO)5I] (1) with KOCN, KSCN, NaPPh2, LiSiMe2Ph, LiN(SiMe3)2, PhCH2MgCl, and KSi6Me11, respectively. Photochemical ligand substitution in W(CO)6 has been used as an alternative method for the preparation of pentacarbonyl tungstates; [K(DIME)2][W(CO)5NCS] (3b), [Na(DIME)2][W(CO)5N3] (5), [Li(DIME)2][W2(CO)10(υ-H)] (6), and [K(DIME)2][W2(CO)10(υ-CN)] (7) were synthesized in this manner. The molecular structure of [Li(DIME)2][W(CO)5Si6Me11] (11) has been determined by X-ray diffraction analysis. The spectral and chemical properties of 2-11 are discussed. Pyrolysis of 11 leads to tungsten silidde and tungsten carbide.
- Palitzsch, Wolfram,Beyer, Christian,B?hme, Uwe,Rittmeister, Ben,Roewer, Gerhard
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p. 1813 - 1820
(2007/10/03)
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- Thermodynamics and Kinetics of MSi2 Formation under Shock Compression
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Thermodynamic and kinetic features of chemical transformation induced by shock compression are considered using reactions of metals with silicon as a model. The mechanisms and topography of processes that occur under cylindrical geometry of dynamic loading are discussed. The electron microscopy data for the shock compression products are reported.
- Batsanov,Gavrilkin,Markis,Meyers
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p. 103 - 109
(2008/10/08)
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- High-Temperature Electrochemical Synthesis of Chromium Family Metal Silicides in Halide-Oxide Melts
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Conditions of high-temperature electrochemical synthesis of chromium, molybdenum, and tungsten silicides as highly disperse powders were found based on a study of the electrochemical behavior of melts containing chromium (molybdenum or tungsten) and silicon.
- Malyshev,Kuprina,Novoselova,Verkhovlyuk
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p. 1888 - 1892
(2008/10/08)
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- SYNTHESIS OF METAL SILICIDE POWDERS BY THERMOLYSIS OF METAL CHLORIDESI WITH MAGNESIUM SILICIDE
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Thermolysis (850 deg C) of a mixture of Mg2Si and MCln (M= Y,Gd,Dy,Ho,Ti,Zr,Hf,Nb,Ta, Mo,W,Fe,Pt; n=3,4,5) produces metal silicides MxSiy, as microcrystalline powders.The reactions give a useful insight into mechanisms working in this type of reaction. Key words: Metal silicide, metal chlorides, magnesium silicide, powder diffraction, thermolysis.
- Fitzmaurice, Jonathan C.,Hector, Andrew L.,Parkin, Ivan P.,Rowley , Adrian T.
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- Growth kinetics of Mo, W, Ti, and Co silicides formed by infrared laser heating
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The growth kinetics of four metal silicides formed by infrared laser heating, MoSi2, WSi2, TiSi2, and CoSi2, were studied. Unfocused (1.4-2.5 mm radii) beams were scanned over thin metal films on Si substrates a
- Lee,Wolga
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p. 684 - 690
(2008/10/08)
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