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Selectivity Failure in the Chemical Vapor Deposition of Tungsten

Description: Tungsten metal is used as an electrical conductor in many modern microelectronic devices. One of the primary motivations for its use is that it can be deposited in thin films by chemical vapor deposition (CVD). CVD is a process whereby a thin film is deposited on a solid substrate by the reaction of a gas-phase molecular precursor. In the case of tungsten chemical vapor deposition (W-CVD) this precursor is commonly tungsten hexafluoride (WF6) which reacts with an appropriate reductant to yield metallic tungsten. A useful characteristic of the W-CVD chemical reactions is that while they proceed rapidly on silicon or metal substrates, they are inhibited on insulating substrates, such as silicon dioxide (Si02). This selectivity may be exploited in the manufacture of microelectronic devices, resulting in the formation of horizontal contacts and vertical vias by a self-aligning process. However, reaction parameters must be rigorously controlled, and even then tungsten nuclei may form on neighboring oxide surfaces after a short incubation time. Such nuclei can easily cause a short circuit or other defect and thereby render the device inoperable. If this loss of selectivity could be controlled in the practical applications of W-CVD, thereby allowing the incorporation of this technique into production, the cost of manufacturing microchips could be lowered. This research was designed to investigate the loss of selectivity for W-CVD in an attempt to understand the processes which lead to its occurrence. The effects of passivating the oxide surface with methanol against the formation of tungsten nuclei were studied. It was found that the methanol dissociates at oxide surface defect sites and blocks such sites from becoming tungsten nucleation sites. The effect of reactant partial pressure ratio on selectivity was also studied. It was found that as the reactant partial pressures are varied there are significant changes in the ...
Date: August 1994
Creator: Cheek, Roger W. (Roger Warren)
Partner: UNT Libraries

Growing carbon nanotubes by chemical vapor deposition technique.

Description: Carbon nanotubes were synthesized in the laboratory using chemical vapor deposition at different methane concentration. I found that a methane concentration of 4 sccm was ideal for well recognizable carbon nanotubes. A higher concentration led to fewer nanotube growth and silicon carbide structure. Coating the sample first with Fe(NO3)3 created a catalyst base on the substrate for the nanotube to adhere and grow on.
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Date: May 2000
Creator: Rajan, Harihar V.
Partner: UNT Libraries

HFCVD of diamond at low substrate and low filament temperatures

Description: It has been discovered that the addition of a small amount of oxygen to the CH{sub 4} and H{sub 2} feed gas permits HFCVD of diamond at significantly lower filament and substrate temperatures. The effective O/C ratio here is much lower than that used in most studies of the oxygen effect. Careful control of the O/C and C/H ratios were found to be crucial to success. The effects of substrate and filament temperatures on growth rate and film quality were studied. Optimum conditions were found that gave reasonable growth rates ( {approximately}0.5 {mu}m/h ) with high film quality at filament temperatures below 1750{degrees}C and substrate temperatures below 600C. As a result, low temperature deposition has been realized. Power consumption can be reduced 50%, and the filament lifetime is extended indefinitely.
Date: March 8, 1995
Creator: Tolt, Z. L.; Heatherly, L.; Clausing, R. E.; Shaw, R. W. & Feigerle, C. S.
Partner: UNT Libraries Government Documents Department

Surface and Interfacial Studies of Metal-Organic Chemical Vapor Deposition of Copper

Description: The nucleation and successful growth of copper (Cu) thin films on diffusion barrier/adhesion promoter substrates during metal-organic chemical vapor deposition (MOCVD) are strongly dependent on the initial Cu precursor-substrate chemistry and surface conditions such as organic contamination and oxidation. This research focuses on the interactions of bis(1,1,1,5,5,5-hexafluoroacetylacetonato)copper(II), [Cu(hfac)2], with polycrystalline tantalum (Ta) and polycrystalline as well as epitaxial titanium nitride (TiN) substrates during Cu MOCVD, under ultra-high vacuum (UHV) conditions and low substrate temperatures (T < 500 K). The results obtained from X-ray photoelectron spectroscopy (XPS), Auger Electron Spectroscopy (AES) and Temperature Programmed Desorption (TPD) measurements indicate substantial differences in the chemical reaction pathways of metallic Cu formation from Cu(hfac)2 on TiN versus Ta surfaces.
Date: December 1997
Creator: Nuesca, Guillermo M.
Partner: UNT Libraries

Scanning Tunneling Microscopy of Homo-Epitaxial Chemical Vapor Deposited Diamond (100) Films

Description: Atomic resolution images of hot-tungsten filament chemical-vapor-deposition (CVD) grown epitaxial diamond (100) films obtained in ultrahigh vacuum (UHV) with a scanning tunneling microscope (STM) are reported. A (2x1) dimer surface reconstruction and amorphous atomic regions were observed on the hydrogen terminated (100) surface. The (2x1) unit cell was measured to be 0.51"0.01 x 0.25"0.01 nm2. The amorphous regions were identified as amorphous carbon. After CVD growth, the surface of the epitaxial films was amorphous at the atomic scale. After 2 minutes of exposure to atomic hydrogen at 30 Torr and the sample temperature at 500° C, the surface was observed to consist of amorphous regions and (2x1) dimer reconstructed regions. After 5 minutes of exposure to atomic hydrogen, the surface was observed to consist mostly of (2x1) dimer reconstructed regions. These observations support a recent model for CVD diamond growth that is based on an amorphous carbon layer that is etched or converted to diamond by atomic hydrogen. With further exposure to atomic hydrogen at 500° C, etch pits were observed in the shape of inverted pyramids with {111} oriented sides. The temperature dependence of atomic hydrogen etching of the diamond (100) surface was also investigated using UHV STM, and it was found that it was highly temperature dependent. Etching with a diamond sample temperature of 200° C produced (100) surfaces that are atomically rough with no large pits, indicating that the hydrogen etch was isotropic at 200° C. Atomic hydrogen etching of the surface with a sample temperature of 500° C produced etch-pits and vacancy islands indicating an anisotropic etch at 500° C. With a sample temperature of 1000° C during the hydrogen etch, the (100) surface was atomically smooth with no pits and few single atomic vacancies, but with vacancy rows predominantly in the direction of the dimer ...
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Date: May 2000
Creator: Stallcup, Richard E.
Partner: UNT Libraries

The Metal-Organic Chemical Vapor Deposition of Cu(II)-bishexafluoroacetylacetonate on a Tungsten Substrate

Description: Evidence is reported for the formation of carbon-containing contamination products at the copper-tungsten (Cu-W) interface during the metal organic chemical vapor deposition (MOCVD) of copper on tungsten. Cu(II)bishexafluoroacetylacetonate [Cu(hfac)_2] was physisorbed onto lightly oxidized tungsten (WO_x) at 115K, under ultra-high vacuum conditions, and then annealed sequentially to higher temperatures. Copper reduction was observed by 320K. Carbonaceous and carbidic contamination of the WO_x surface was observed, even after sample warming to 625K in UHV. The results indicate that low temperature MOCVD of Cu may be possible, but interfacial contamination from the organic ligand fragmentation is a major concern.
Date: May 1992
Creator: Welton, Theresa E. (Theresa Eilene)
Partner: UNT Libraries

Interrelationships between process parameters, structure, and properties of CVD tungsten and tungsten--rhenium alloys

Description: From conference on structure-property relationships in thick film and bulk coatings; San Francisco, California, USA (28 Jan The development of CVD techniques for fabricating free-standing tungsten and tungsten - rhenium alloy structures is reviewed. Relationships between plating parameters, kinetics, morphology, microstructure, and properties of thick polycrystalline deposits are discussed. It is emphasized that porosity may be grown into the grain boundaries when the deposition rate is cortrolled by gas phase diffusion, and that fully dense deposits are generally obtained when the rate is limited by a surface process. The origin and control of many of the microstructural features peculiar to CVD are also discussed. (11 figures) (auth)
Date: December 1, 1973
Creator: Holman, W.R. & Huegel, F.J.
Partner: UNT Libraries Government Documents Department

Growth of InSb on GaAs Using InAlSb Buffer Layers

Description: We report the growth of InSb on GaAs using InAlSb buffers of high interest for magnetic field sensors. We have grown samples by metal-organic chemical vapor deposition consisting of {approximately} 0.55 {micro}m thick InSb layers with resistive InAlSb buffers on GaAs substrates with measured electron nobilities of {approximately}40,000 cm{sup 2}/V.s. We have investigated the In{sub 1{minus}x}Al{sub x}Sb buffers for compositions x{le}0.22 and have found that the best results are obtained near x=0.12 due to the tradeoff of buffer layer bandgap and lattice mismatch.
Date: September 20, 1999
Partner: UNT Libraries Government Documents Department

Optimization of transparent and reflecting electrodes for amorphous silicon solar cells. Final technical report

Description: Transparent conducting fluorine doped zinc oxide was deposited as thin films on soda lime glass substrates by atmospheric pressure chemical vapor deposition (CVD) at substrate temperatures of 460 to 500 degrees C. The precursors diethylzinc, tetramethylethylenediamine and benzoyl fluoride were dissolved in xylene. This solution was nebulized ultrasonically and then flash vaporized by a carrier gas of nitrogen preheated to 150 degrees C. Ethanol was vaporized separately, and these vapors were then mixed to form a homogeneous vapor mixture. Good reproducibility was achieved using this new CVD method. Uniform thicknesses were obtained by moving the heated glass substrates through the deposition zone. The best electrically and optical properties were obtained when the precursor solution was aged for more than a week before use. The films were polycrystalline and highly oriented with the c-axis perpendicular to the substrate. More than 90% of the incorporated fluorine atoms were electrically active as n-type dopants. The electrical resistivity of the films was as low as 5 x 10/sup -4/ Omega cm. The mobility was about 45 cm ²/Vs. The electron concentration was up to 3 x 10 %sup20;/cm³. The optical absorption of the films was about 3-4% at a sheet resistance of 7 ohms/square. The diffuse transmittance was about 10% at a wavelength of 650 nm. Amorphous ilicon solar cells were deposited using the textured fluorine doped zinc oxide films as a front electrode. The short circuit current was increased over similar cells made with fluorine doped tin oxide, but the open circuit voltages and fill factors were reduced. The voltage was restored by overcoating the fluorine-doped zinc oxide with a thin layer of fluorine-doped tin oxide.
Date: September 1, 1998
Creator: Gordon, R. G.; Kramer, K.; Liang, H.; Liu, X.; Pang, D. & Teff, D.
Partner: UNT Libraries Government Documents Department

Centimeter Scale Patterned Growth of Vertically Stacked Few Layer Only 2D MoS₂/WS₂ van der Waals Heterostructure

Description: This article reports the chemical vapor deposition (CVD) growth of large-area (>2 cm²) patterned 2D vdW heterostructures composed of few layer, vertically-stacked molybdenum disulfide and tungsten disulfide.
Date: May 5, 2016
Creator: Choudhary, Nitin; Park, Juhong; Hwang, Jun Yeon; Chung, Hee-Suk; Dumas, Kenneth H.; Khondaker, Saiful I. et al.
Partner: UNT College of Engineering

GaAs Self-Aligned JFETS with Carbon-Doped P+ Region

Description: Self-aligned JFETs with a carbon-doped p{sup +} region have been reported for the first time. For these JFETs, both the channel and p{sup +} region were grown by metal organic chemical vapor deposition (MOCVD) and are termed epitaxial JFETs in this study. The epitaxial JFETs were compared to ion implanted JFETs of similar channel doping and threshold voltage. Both JFETs were fabricated using the same self-aligned process for doping the source and drain regions of the JFET and for eliminating excess gate capacitance of conventional JFETs. The gate turn-on voltage for the epitaxial JFETs was 1.06 V, about 0.1 V higher than for the implanted JFETs. The reverse breakdown voltage was similar for both JFETs but the reverse gate leakage current of the epitaxial JFETs was 1-3 orders of magnitude less than the implanted JFETs. The epitaxial JFETs also showed higher transconductance and lower knee voltage than the implanted JFETs.
Date: February 15, 1999
Creator: Allerman, A.A.; Baca, A.G.; Chang, P.C. & Drummond, T.J.
Partner: UNT Libraries Government Documents Department

GaN pnp bipolar junction transistors operated to 250 C

Description: The authors report on the dc performance of the first GaN pnp bipolar junction transistor. The structure was grown by MOCVD on c-plane sapphire substrates and mesas formed by low damage Inductively Coupled Plasma etching with a Cl{sub 2}/Ar chemistry. The dc characteristics were measured up to V{sub BC} of 65 V in common base mode and at temperatures up to 250 C. Under all conditions, I{sub C} {approximately} I{sub E}, indicating higher emitter injection efficiency. The offset voltage was {le} 2 V and devices were operated up to power densities of 40kW{center{underscore}dot}cm{sup {minus}2}.
Date: January 3, 2000
Creator: Zhang, A.P.; Dang, G.; Ren, F.; Han, J.; Monier, C.; Baca, A.G. et al.
Partner: UNT Libraries Government Documents Department

Effect of carrier gas on the surface of morphology and mosaic dispersion for GaN films by low-pressure MOCVD

Description: Low-pressure metal-organic chemical vapor deposition (MOCVD) has been used to deposit unnucleated and self-nucleated GaN thin films on (00.1) sapphire substrates. For the self-nucleated films, initial layers were grown at 540{degrees}C using trimethylgallium and ammonia as elemental sources and either nitrogen or hydrogen as the carrier gas. Using these same gas phase conditions, overlayers on native (00.1) sapphire substrates or the GaN-nucleated (00.1) sapphire substrates were deposited at 1025{degrees}C. The surface morphology and mosaic dispersion of these unnucleated and self-nucleated GaN thin films have been surveyed by a combination of real space images from atomic force microscopy and reciprocal space intensity data from X-ray scattering measurements. As expected, the unnucleated GaN films show a large-grained hexagonal relief, typical of three-dimensional island growth. However, the self-nucleated films are shown to be dense mosaics of highly oriented islands, emblematic of a more two-dimensional growth.
Date: December 31, 1995
Creator: Kistenmacher, T.J.; Wickerden, D.K.; Hawley, M.E. & Leavitt, R.P.
Partner: UNT Libraries Government Documents Department

Molecular-jet chemical vapor deposition of SiC

Description: SiC films have been deposited by molecular-jet chemical vapor deposition (MJCVD) on Si(001) substrates. Methylsilane (MS) diluted in He was used as a precursor for deposition under conditions which produced a MS molecular beam with 0.365 eV translational energy. Films grown at temperatures between 1000 and 1150 C and above {approx}1200 C were single crystal as judged by electron channeling, while those grown at intermediate temperatures were polycrystalline. Films grown at lower temperatures generally had a smoother surface morphology for moderate thicknesses, although all films showed at least some degree of faceting. The best thick films, up to 4 {mu}m, were obtained for substrate temperatures of {approx}1210 C under flow conditions which produced a deposition rate of {approx}1200 {angstrom} per minute.
Date: September 1, 1995
Creator: Lubben, D.; Jellison, G.E. & Modine, F.A.
Partner: UNT Libraries Government Documents Department

GaN Stress Evolution During Metal-Organic Chemical Vapor Deposition

Description: The evolution of stress in gallium nitride films on sapphire has been measured in real- time during metal organic chemical vapor deposition. In spite of the 161%0 compressive lattice mismatch of GaN to sapphire, we find that GaN consistently grows in tension at 1050"C. Furthermore, in-situ stress monitoring indicates that there is no measurable relaxation of the tensile growth stress during annealing or thermal cycling.
Date: October 14, 1998
Creator: Amano, H.; Chason, E.; Figiel, J.; Floro, J.A.; Han, J.; Hearne, S. et al.
Partner: UNT Libraries Government Documents Department

Thermochemistry of gas-phase species relevant to titanium nitride CVD

Description: In this work, three different ab initio methods are used to predict bond dissociation enthalpies (BDE) and atomization energies for TiCl{sub n} (n = 1-4) and Ti(NH{sub 2})n (n = 1-4) compounds, as well as for the complex TiCl{sub 4}:NH{sub 3}. There is considerable variation in the predicted BDES, even for highly electron-correlated methods. However, bond-additivity corrections applied to coupled-cluster calculations at the CCSD(T) level, expected to be the most reliable of the three methods, yield Ti-Cl BDEs in good agreement with experimental results. An experimental estimate of the TiCl{sub 4} BDE is also reported that is consistent with the ab initio results and recent experiments by others indicating that the TiCl{sub 3} heat of formation reported in the JANAF Tables is too low. Finally, the predicted BDEs indicate that the gas-phase reaction of TiCl{sub 4} and NH{sub 3} to form the complex Cl{sub 4}Ti:NH{sub 3} is exothermic by 17 kcal mol{sub {minus}1}. In addition, decomposition of the complex to form Cl{sub 3}TiNH{sub 2} and HCl is endothermic by 20 kcal mol{sup {minus}1}.
Date: June 1, 1995
Creator: Allendorf, M.D.; Janssen, C.L.; Colvin, M.E.; Melius, C.F.; Nielsen, I.M.B.; Osterheld, T.H. et al.
Partner: UNT Libraries Government Documents Department

Progress Report - Project 31: Vapor Phase Chlorination of TO₃

Description: "This work is a continuation of an investigation begun in January, 1945, on a laboratory study of various methods for the chlorination of TO3. The work carried out this month deals entirely with gas phase chlorination, the liquid phase chlorination of TO3 having been turned over to Miss Hubbard. Gas phase chlorination of TO3 by means of CCl4, S2Cl2, SOCl2, SO2Cl2, and Cl2 have been carried out under varying conditions in the several different types of reactors."
Date: April 2, 1945
Creator: Parsons, George S.; McCabe, Charles Law.; Engle, G. F. & Larson, C. E.
Partner: UNT Libraries Government Documents Department