Chemical Vapour Deposition of YBa2Cu3O7−x superconductors using organometallic precursor materials involves the formation of a great variety of condensed phases (oxides, carbonates, hydroxides, carbides, hydrides) and a complex gas phase. Therefore, the possibility of calculating the stability ranges of the different phases susceptible of being deposited and the influence of the main experimental parameters (precursor partial pressure, oxygen partial pressure, total pressure, temperature) is very attractive. Recently, some initial attempts have been published, but the authors did not have sufficiently complete and reliable thermodynamic data on the species involved in the process. These results will be discussed. Furthermore, a homogeneous and complete set of data for the whole system will be presented, and the reactions of the deposition process will be simulated on the basis of this data set. The most important results will be compared to the previous calculations and to recent experimental work.

The gas-phase chemical reaction between Ti(NMe2)4 and NH3 is a critical step in the Metallorganic Chemical Vapor Deposition (MOCVD) of TiN at low temperatures. We have examined this reaction using a flow-tube reactor coupled to an FTIR spectrometer. A sliding injector provides control over the reaction time and the kinetics of reactive species can be measured as a function of the partial pressure of an added reagent. The disappearance of Ti(NMe2)4 was measured as a function of reaction time and NH3 pressure at 26°C. The resulting bimolecular rate constant is (1.1±0. 1) x 10-16 cm3molecules−1s−1 Dimethylamine is observed as a direct product from this reaction consistent with other studies. We have also measured the rate constant using ND3 and find a substantial isotope effect, kh/kd ≈2.4± 0.4. This indicates that H-atom transfer is involved in the rate limiting step. We show that these results can be explained by a mechanism comprised of transamination reactions with NH3.

In spite of several attempts, superconducting Tl-Ba-Ca-Cu-O thin films have not been successfully prepared in situ by metal organic chemical vapor deposition (MOCVD). Preparation of a phase by MOCVD requires that it be thermodynamically stable with respect to its decomposition into volatile species and other condensed phases. For MOCVD growth of Tl-Ba- Ca-Cu-O compounds in the presence of oxygen from reagents containing only C-H or C-H-O ligands, Tl2O(g) and TIOH(g) exhibit appreciable volatility. If reagents with ligands containing fluorine are used, the formation of volatile TIF(g) must also be considered. Thermodynamic data for these materials are compiled, and thermodynamic relationships between these gases, H2O(g) and HF(g) are established. The thermodynamic stability of TIOH(g) and TIF(g) makes the in situ growth of Tl-Ba-Ca-Cu-O compounds by MOCVD more difficult than their in situ growth by physical vapor deposition processes, for which Tl2O(g) is the only volatile TI-containing species present.

We model a cold-wall atmospheric pressure impinging jet reactor to study the CVD and gas-phase nucleation of TiO2 from a titanium tetra-iso-propoxide (TTIP)/oxygen dilute source gas mixture in nitrogen. The mathematical model uses the computational code FIDAP and complements our recent asymptotic theory for high activation energy gas-phase reactions in thin chemically reacting sublayers. The numerical predictions highlight deviations from ideality in various regions inside the experimental reactor. Model predictions of deposition rates and the onset of gas-phase nucleation compare favorably with experiments. Although variable property effects on deposition rates are not significant (∼11% at 1000K), the reduction of rates due to Soret transport is substantial (∼75% at 1000K).

A theoretical model, which describes the coupled hydrodynamics, mass transport and chemical reaction, has been developed to simulate chemical vapor deposition (CVD) of silicon carbide (SiC) from gas mixture of methyltrichlorosilane (MTS), hydrogen and argon in a hot wall reactor. In the model analysis, the governing equations were developed in the cylindrical coordinate, and solved numerically by using a finite difference method. A kinetic rate expression of CVD-SiC deposition from the gas mixture was obtained from this study. The deposition rate has an Arrhenius-type dependence on the deposition temperature and is first order with respect to the MTS concentration. Estimated activation energy is 254 kJ/mol. Predicted deposition rate profiles by the model analysis incorporated with the obtained kinetic rate expression showed excellent agreement with experimental data over a variety of applied deposition conditions.

β–SiC thin films were epitaxially grown on porous Si(100) substrates at 1150° C from methyltrichlorosilane (CH3SiCl3 or MTS) in a hot wall reactor by Vsing low pressure chemical vapor deposition (LPCVD). The growth rate was 120 Å/min. Epitaxial β–SiC(100) thin films were obtained after a deposition time of 12.5 min. The crystallinity of the β–SiC films was affected by the deposition time. For instance, rotational β–SiC(100) crystals and polycrystalline β–SiC with a highly preferred orientation of (100) planes were observed for a deposition time of 50 min. The results from XRD and TEM indicated that polycrystalline β–SiC films with a preferred orientation of β–SiC(111) appeared after further increasing the deposition times (time ≥ 75 min). The change in crystallinity is attributed to increasing roughness with increasing deposition time.

In recent years much attention has been given world-wide to the development of suitable MOCVD precursors for the deposition of HTcS thin films. Synthetic research has been and is concentrated on the development of superior Ba-, Sr-, Ca- and Y-precursors. Most emphasis is given to the synthesis of thermally stable volatile barium compounds. Synthetic strategies are based on encapsulating the central metal atom, by use of multidentate ligand systems and/or bulky substituents. Most attention is given to the development of thermally stable volatile ß-diketonate complexes, fluorine-free and fluorine-substituted, with auxiliary ligands. Thermally stable monomeric complexes of fluorine-substituted ß-diketonates with polyethers are by far the most volatile Ba-, Sr-, and Ca-precursors presently available. Low melting Y(thd)3.L complexes where L is 4-Et- or 4-t-Bupyridine- N-oxide can be used as liquid yttrium MOCVD precursors at temperatures above 100°C. This paper gives a survey of the trends in recent research activity and developments in these areas.

Barium titanate and barium-strontium titanate (BST) are high dielectric materials, likely to replace state-of-the-art capacitor materials for memory applications. Chemical Vapor Deposition (CVD) of these materials has been hampered, particularly by the lack of suitable precursors for barium. Although attempts to make volatile metal-organic barium compounds have met with some progress, a suitably stable, volatile barium source is still in demand. This paper will highlight recent developments at ATM, including syntheses and structures of polyamine and glycol ether adducts which have been designed to limit aggregation of barium diketonates, and stabilize the adducts with respect to ligand dissociation.

Epitaxial thin layers of YBa 2Cu 3O7−x (Tc=90 K, Jc (OT, 77 K) = 2 106 A cm-2) were synthesised by thermal decomposition (750 − 830 °C) of tetramethylheptanedionates of yttrium, barium and copper in the presence of oxygen. Three different precursor delivery systems have been used: In the first, the precursor's surface is flushed with the carrier gas (Ar), in the second, argon is directly injected through the powder leading to a much higher transport rate, and in the third, a liquid (diketonates in a solvent) is nebulized via a piezoelectric transducer. The transport and deposition rates obtained in these three different reactors will be compared.

Lead bis-tetramethylheptadionate (Pb(thd)2) is an extremely useful precursor for the preparation of lead-based thin films such as PZT, lead titanate, etc. In this paper, lead oxide was deposited from Pb(thd)2 in a hot-walled CVD reactor using oxygen as a reactive species and diluent gas. XRD and SEM were used to determine the structure of the material deposited by the CVD process. The CVD process consistently produced the monoxide of lead which was found to consist of a mixture of orthorhombic PbO with small tetragonal PbO platelets. TEM was used to determine the orientation of the individual platelets which was found to be consistently normal to the <201> family of zone axes. Deposition rates were determined and simulated using an FEM computer model to determine the rate constants for the overall deposition process.

A significant limitation in MOCVD processing of advanced materials is the ability to deliver low volatility precursors, in a repeatable fashion, to the deposition reactor. Apparatus for delivering low volatility precursors in gaseous form, wherein a precursor source liquid is flash vaporized at elevated temperature has been developed. Stable, reproducible delivery of liquid precursors for TiN and Ta2O5 has been demonstrated. For multicomponent ceramic material systems simultaneous delivery of multiple cation species via a single source liquid has been achieved. The effect of flash vaporization on precursors for PZT was investigated. Pb, Zr and Ti precursors were dissolved in an organic medium with a defined cation ratio. The source solution was vaporized, the precursors transported as vapor then collected and analyzed by 1H and 13C nmr. No decomposition of the precursors was observed post vaporization and source solution stoichiometry was maintained in the collected material. The use of this flash vaporization technique has already been particularly successful for MOCVD of BaTiO3, MgAl2O4, YBa2Cu3O7−x, YSZ, LaSrCoO3 and Cu metal.

Reaction of metallic indium with benzoyl peroxide in 4-methylpyridine (4-Mepy) at 25 °C produces an eight-coordinate mononuclear indium(III) benzoate, In(η2-O2CC6H5)3(4- Mepy)2 4H2O (I), in yields of up to 60%. The indium(III) benzoate was fully characterized by elemental analysis, spectroscopy, and X-ray crystallography; (I) exists in the crystalline state as discrete eight-coordinate molecules; the coordination sphere around the central indium atom is best described as pseudo-square pyramidal. Thermogravimetric analysis of (I) and X-ray diffraction powder studies on the resulting pyrolysate demonstrate that this new benzoate is an inorganic precursor to indium oxide. Decomposition of (I) occurs first by loss of 4-methylpyridine ligands (100°-200°C), then loss of benzoates with formation of In2O3 at 450°C. We discuss both use of carboxylates as precursors and our approach to their preparation.

The traditional CVD phase diagrams are only valid for cold wall reactors because of the neglecting of the depletion effects in hot wall reactors. Due to the depletion effects along the reactor, the traditional CVD phase diagrams can not accurately predict the phases deposited on the substrate in a hot wall CVD system. In this paper, a new approach to calculate the local equilibrium CVD phase diagrams in a hot wall reactor is presented by combining the depletion effects with the equilibrium thermodynamic computer codes (SOLGASMIX–PV). In this study, the deposition of SiC using methyltrichlorosilane (MTS)–hydrogen (H2) was chosen to verify this new approach. The differences between the new CVD phase diagrams and the traditional phase diagrams were discussed. The calculated CVD phase diagrams were also compared with the experimental data. The single phase of SiC predicted by this approach is much better than the traditional phase diagrams. The experimental regions for depositing single phase SiC are larger than the calculated local phase diagrams because of the higher linear velocity of the gas flux under low pressure and the polarity of the Si carrying intermediate species.

The vertical, high speed, rotating disk reactor (RDR) has, in recent years, found broad application in the Metalorganic Chemical Vapor Deposition of a variety of material systems. These applications include epitaxial films of III-V and II-VI compound semiconductors, oxides (such as YBCO superconductors/ferroelectrics and SiO2, amongst others), Group IV materials (such as diamond and SiC), and metals (such as copper and tungsten). As production of these material systems increases, so too does the need for economical, high yield equipment capable of producing these materials with high levels of uniformity and repeatability. We have used computational fluid dynamic modeling to investigate the complex flow and thermal dynamics required for scaling existing RDRs (as large as a 7.25″ diameter disk handling up to 3×3″ wafers) to larger dimensions (11″ and 12″ diameter disks for multiple 4″ and 15.5″ diameter disk for 3×6″ wafers). The scaling parameters predicted by the modeling codes are reviewed and correlate well with experimental results. Materials results on GaAs films using TBAs, TMGa, and TMA1 for the 11″ diameter system routinely demonstrate within wafer thickness uniformities of <1.1% for 3×4″ wafers, as well as for 6″ or 8″ diameters, wafer to wafer uniformities <1% and run to run repeatabilities within 1%. These results are verified by SEM analysis, as well as with GaAs/AJGaAs Bragg reflectors. The excellent results on the 11″ and 15.5″ diameter platters combined with modeling indicated that 4×4″ wafers on a 12″ diameter platter would produce ideal films which, indeed, is the case. The 11″ diameter results have been surpassed, demonstrating <0.9% for >9″ diameters (4×4″ wafers) on a 12″ diameter susceptor. With high reactant efficiencies (>3 6%), short cycle times between growths using the loadlock, and minimal maintenance requirements, the costs per wafer in a cost of ownership model are found to be dramatically less than in competitive technologies.

In this paper we first give a brief overview of the MOCVD of high temperature superconductors and consider the general requirements of a precursor. We then present results for deposition from Y containing precursors and compare apparent enthalpies of sublimation and deposition activation energies with values in the literature. The problem of Ba containing precursors are briefly reviewed and results given for the sublimation of and deposition from a new stable and volatile precursor. Finally, some comments are made about possible deposition mechanisms.

The plasma-enhanced MOCVD is developed to prepare high-Tc oxide superconducting thin films. Plasmas generated by microwave and rf discharges decompose effectively the source materials ( β-diketonate chelates) into their elements and oxides. YBaCuO thin films were deposited on the MgO substrate of 500–650 °C at total pressure of 0.6–5 Torr with O2 contents less than 30%. The as-grown films produced by two kinds of plasma enhancement were porous and consisted of crystalline grains, but showed the superconducting transition after heating procedure at around 800 °C. It is shown that the inherent crystalline orientations of the as-grown films determine the crystal structure of the post-annealed films. The film of the metal atomic ratios of 0.91 for Ba/Y and 2.64 for Cu/Y showed the superconducting properties with Tc(zero) of 89 K and the critical current density (at 77 K) of 5×104 A/cm2. Spectroscopic analysis showed that the plasmas are composed of many excited species such as Y, Y+, Ba, Ba+, Cu, YO, BaO, CuO. Formation of the metal-oxides through the gas phase reaction is essential for the high-quality YBaCuO superconducting thin film preparation in the PEMOCVD.

Superconducting thin films of Tl2Ba2Ca2Cu3O10−x (TL-2223) have been grown on single crystal (110) LaAlO3 using a two-step process. Ba2Ca2Cu3Ox precursor films are deposited via metal-organic chemical vapor deposition (MOCVD) in a horizontal hot walled reactor. The second generation precursors Ba(hfa)2•tet, Ca(hfa)2•tet, and Cu(hfa)2 (hfa = hexafluoroacetylacetonate, tet = tetraglyme) were used as volatile metal sources due to their superior volatility and stability. Tl was introduced into the film via a high temperature post anneal in the presence of a Tl2O3:BaO:CaO:CuO pellet (1:2:2:3 ratio). Low O2 partial pressures were used to reduce the temperature in which the TI-2223 phase forms and to improve the surface morphology associated with a liquid phase intermediate. Films are highly oriented with the c-axis perpendicular to the substrate and a-b axis epitaxy is seen from x-ray φ- scans. The best films have a resistively measured Tc of 115K and a magnetically derived Jc of 6×105 A/cm2 (77K, 0 T). Preliminary surface resistance measurements, using parallel plate techniques, give Rs = 0.35 mΩ at 5K (ω = 10 GHz).

Metalorganic chemical vapor deposition (MOCVD) is emerging as a practical high Tc superconducting thin film preparation technique for industrial application. Intrinsically this technique involves a large number of variable parameters. This is especially critical for the quarternary or higher high Tc materials. Thus, effective methods are required to optimize the parameters for the preparation of high Tc films. A matrix experimental design named Robust Design has been employed for this purpose. The first-phase design was based on a starting knowledge of growth temperature and pressure, and annealing temperature for MOCVD preparation of YBCO thin films. A minimum lab effort of only nine deposition experiments was then used to optimize the process control parameters of precursor oven temperature, carrier gas (Ar) flow rate, O2 flow rate and N2O flow rate. The results were then followed by three confirmation depositions. The Robust Design resulted in the growth of YBCO film with Tc consistently in the range of 87.0 K to 90.2 K and Jc improved from about 1.0 × 106 A/cm2 to 3–5 × 106 A/cm2.

Bi2Sr2CaCu2O8 thin films have been prepared in situ by low pressure metalorganic chemical vapor deposition using fluorinated β–diketonate precursors. The influence of the growth conditions on the oxide phase stability and impurity phase formation was examined as well as the superconducting properties of the films. Thin films deposited on LaAIO3 substrates were epitaxial as confirmed by x-ray diffraction measurements, including θ-2θ and φ scans. Four probe resistivity measurements showed the films to be superconducting with a maximum Tc0 of 90 K without post annealing. This Tc0 is among the highest reported for thin films of the BSCCO (2212) phase, and approaches reported bulk values.

Low-temperature growth of YBa2Cu3Ox films by metalorganic chemical vapor deposition using N2O as an oxidizing agent has been investigated. We have deposited superconducting YBa2Cu3Ox on (100)MgO substrates at 500°C for the first time. Films of 15nm-thick show zero-resistivity critical temperature of 80K. Films of as thin as three unit-cell-thick reveal the superconducting onset characteristics. This result suggests that superconductivity is arisen even from effectively monomolecular layer of YBa2Cu3Ox when we take into account monomolecular buffer layer and monomolecular cap layer. YBa2Cu3Ox films of 9nm-thick grown on (100)SrTiO3 at 600°C with Tc(zero) of 79K and with peak to valley roughness fluctuation of two unit-cell have been obtained.