Chemical vapour deposition of epitaxial ZnO films

Heteroepitaxial growth of ZnO on sapphire has been studied, using the (H₂HClZnO) vapour growth technique. A systematic study of the influence of the substrate orientation and temperature of growth on the quality of the films has been carried out. The surface morphology of the grown layer was strongly dependent on substrate orientation and growth anisotropy.     

Preparation of nickel and Ni-Zn ferrite films by thermal decomposition of metal acetylacetonates

Nickel and Ni-Zn ferrite (Ni_1–x Zn _x Fe₂O₄) films were prepared on various substrates (quartz glass, MgO single crystal, etc.) by thermal decomposition of metal acetylacetonates (Ni (acac)₂ · 2H₂O, Zn (acac)₂ · 2H₂O and Fe (acac)₃). Typical decomposition and heat treatment conditions for obtaining a single phase of NiFe₂O₄ film were as follows: evaporation temperature of Ni-Fe complexes: 230°C, the mole concentration of Fe (acac)₃,R (%) = Fe (acac)₃/(Fe (acac)₃ + Ni (acac)₂ · 2H₂O) = 33, substrate temperature: 330 to 550° C, and heat treatment of the as-grown film: 800 to 1000° C, 1 h. Ni_1–x Zn _x Fe₂O₄ films were obtained by controlling the compositionR in Ni-Fe complexes and the evaporation temperature of Zn (acac)₂ · 2H₂O. The Ni-Zn ferrite film at the compositionx = 0.37 (Ni_0.63Zn_0.37Fe₂O₄) gave the maximum saturation magnetization _s = 60 emu g^–1 and the coercive forceHc 25 Oe. These films showed a magnetic anisotropy which makes the magnetization easy parallel to film surface.     

Defects in nickel ferrite thin films grown by chemical vapour deposition

Thin single-crystal films of nickel ferrite have been grown on magnesia substrates. The structure of the films has been examined using X-ray diffraction, scanning electron microscopy and transmission electron microscopy and diffraction. The films are characterized by arrays of planar faults on {110} due to faults in cation arrangements in the nickel ferrite spinel lattice. The origin of these defects is discussed.     

Chemical vapor deposition of epitaxial garnet films

The chemical vapor deposition of single crystal metal oxides has recently been extended to the growth of certain epitaxial garnets, in particular YIG on YAG and GdIG on YAG. The light green, transparent films aresim3muthick and are limited in area only by the area of the available YAG seeds. On     

Chemical vapour deposition of nitrogen-doped titanium dioxide thin films

Nitrogen-doped titanium dioxide is often considered as a promising nanomaterial for photocatalytic applications. Here we report the first results of a study of APCVD of N-doped TiO2 thin films prepared with the use of ammonia as a source of nitrogen and titanium tetraisopropoxide (TTIP) as a source of Ti and O atoms. The obtained films were analyzed with X-ray diffraction, infrared spectroscopy, atomic force microscopy, X-ray photoelectron spectroscopy, UV-Vis spectroscopy, and ellipsometry. It was found that the film growth rate in the TTIP-NH3-Ar reaction system varied insignificantly with substrate temperature in the range of 450,..., 750 degrees C and did not exceed 4.4 nm/min. Yellow and orange layers with nitrogen content of about 7.6% were formed at the deposition temperature higher than 600 degrees C. The results of the structure analysis of the deposited films showed that addition of ammonia led to stabilization of the amorphous phase in the films. The effect of ammonia on optical and photocatalytic properties was also considered.     

Magnetic-field-induced phase separation via spinodal decomposition in epitaxial manganese ferrite thin films

In this study, we report about the occurrence of phase separation through spinodal decomposition (SD) in spinel manganese ferrite (Mn ferrite) thin films grown by Dynamic Aurora pulsed laser deposition. The driving force behind this SD in Mn ferrite films is considered to be an ion-impingement-enhanced diffusion that is induced by the application of magnetic field during film growth. The phase separation to Mn-rich and Fe-rich phases in Mn ferrite films is confirmed from the Bragg’s peak splitting and the appearance of the patterned checkerboard-like domain in the surface. In the cross-sectional microstructure analysis, the distribution of Mn and Fe-signals alternately changes along the lateral (x and y) directions, while it is almost homogeneous in the z-direction. The result suggests that columnar-type phase separation occurs by the up-hill diffusion only along the in-plane directions. The propagation of a quasi-sinusoidal compositional wave in the lateral directions is confirmed from spatially resolved chemical composition analysis, which strongly demonstrates the occurrence of phase separation via SD. It is also found that the composition of Mn-rich and Fe-rich phases in phase-separated Mn ferrite thin films deposited at higher growth temperature and in situ magnetic field does not depend on the corresponding average film composition.     

Chemical vapour deposition of Ca(Ti,Fe)O3 thin film by thermal decomposition of organocomplexes

A thin film of Ca(Ti, Fe)O₃, which is a mixed conductor of oxide ions and electrons, was prepared on various substrates by chemical vapour deposition using organocomplexes Ca(C₁₁H₁₉O₂)₂, Ti(O-ⁱC₃H₇)₄ and Fe(C₅H₇O₂)₃ as starting materials. These complexes were evaporated at temperatures of 250, 115 and 45 °C, respectively, and transported to the substrate surface at an almost steady state. Homogeneous films of single-phase Ca(Ti, Fe)O₃ were obtained at deposition temperatures of 750–800 °C under the total pressure of 30 torr for the reaction time of 60–90 min on silica glass substrate. The amount of Ca(Ti, Fe)₃ films formed and their microstructure were found to be greatly affected by the compositions and surface structures of substrate materials.     

Photostructural transformations in amorphous chalkogenide nanolayered films produced by thermal vapour deposition

Photo- and thermoinduced changes of As₂S₃ \Se_xTe_1−x (0.1 < x < 0.5) multilayer structures were investigated by optical and electrical methods as well as by low angle X-ray diffraction (LAXD). It was shown that samples with total thicknesses up to 0.7–0.8 μm of 4–20 nm thick alternating layers with good periodicity, may be prepared by cyclic thermal vapour deposition. The structure of this multilayer may be changed by thermal treatment or illumination with focused laser beam due to the interdiffusion. The corresponding photoinduced changes of optical parameters (absorption, refraction) are useful for optical reading.     

Chemical vapour deposition (CVD) of borophosphosilicate glass films

Chemical vapour deposition (CVD) has become the standard method for the fabrication of microelectronic devices for use in the semiconductor industry. In this investigation, it has been used to grow films of silicon dioxide (SiO₂) and borophosphosilicate glass (BPSG) at both atmospheric and low pressures under various conditions. The growth behaviour of SiO₂ and BPSG films has been investigated as a function of the O₂/SiH₄ ratio. Both processes give a similar trend, with the growth rates of BPSG being somewhat higher than SiO₂. The variation in the growth rate with O₂/SiH₄ ratio has been explained in terms of relative transport and kinetic reaction rates. The effects of temperature on the deposition rate have also been studied and the activation energy calculated showed two distinct regions corresponding to mass transport control and kinetic control regimes. Both BPSG and SiO₂ have been annealed under various furnacing conditions. It has been shown that the addition of boron and phosphorous results in much lower reflow temperatures and times. This has a significant bearing on the performance characteristics of devices. Initial results from rapid thermal annealing (RTA) work are also presented, and RTA is shown to be a viable annealing process.     

Chemical vapour deposition of tungsten films for metallization of integrated circuits

New materials and processes are required for the metallization of very large- scale integrated circuits. Tungsten offers several advantages as a contact barrier, low resistance gate material and metal for interconnections. Conventional, plasma- enhanced and laser-induced chemical vapour deposition processes used to produce tungsten films are described. The basic reactions involved are either pyrolysis of the carbonyl (W(CO)₆) or reduction of halides (WCl₆ and WF₆). The mechanism of tungsten deposition via the H₂ and silicon reduction of WF₆ is discussed. The physical properties of tungsten films (resistivity, W-Si contact resistance) and the charateristics of Schottky barrier diodes and W/SiO₂/Si structures are reviewed. The chemical properties of tungsten films, including W-Si reactivity (thermal stability of W-Si contacts) and suitable etching solutions are presented. Several applications of tungsten films for metallization of integrated circuits are examined.     

Chemical vapour deposition of PbTiO3 films onto TiO2-Si

Ferroelectric lead titanate thin films were deposited on the TiO₂ coated Si(100) substrate by chemical vapour deposition under atmospheric pressure. We have used Pb powder and tetraethyle-orthotitanate [Ti(C₂H₅O)₄] as the source material of Pb and Ti vapour. We investigated the variations of the phase of deposited films with the Ti(C₂H₅O)₄ input fractions. When the mole fraction was 0.021, PbTiO₃ single phase was obtained. For the other Ti(C₂H₅O)₄ input fractions, we could find PbO solid solutions phase in addition to the PbTiO₃ phase. The results of AES analysis revealed that the TiO₂ layer on the Si substrate acted as diffusion barriers between Si substrate and PbTiO₃ films.     

Preparation of BN films by r.f. thermal plasma chemical vapour deposition

Boron nitride films were prepared at 1 atm by r.f. thermal plasma chemical vapour deposition from the gas systems of Ar-BF₃-N₂ (or NH₃, NF₃)-H₂, Ar-BCl₃-N₂ (or NH₃, NF₃)-H₂, and Ar-B₂H₆-N₂ (or NH₃)-H₂. The appearance and the deposition rate of the films changed drastically with the composition of the feed gas. Only from the Ar-BF₃-N₂(-NF₃) gas, were transparent and smooth films obtained, while from other gas systems, white flaky or powder-like deposits formed. The structure of these films was basically sp²-bonded turbostratic BN, and the formation of cubic BN was not confirmed.     

Chemical stability of hydrogen-containing boron nitride films obtained by plasma enhanced chemical vapour deposition

The purpose of this paper is the investigation of the dehydrogenation kinetics of boron nitride films during thermal annealing. BN_x:H films on silicon substrates were prepared by remote plasma enhanced chemical vapour deposition at 473 K using a mixture of borazine and helium. IR spectroscopy and ellipsometry were used to characterize the film properties and composition. The films contain a certain amount of hydrogen in B---H and N---H bonds. The breakage kinetics of these bonds is different. The breakage of N---H bonds determines the hydrogen annealing kinetics at 973–1073 K. The low-temperature annealing (673–873 K) of B---H bonds is sensitive to the generation of hydrogen from N---H bonds. Heat treatment leads to ordering of the films.     

Chemical vapour deposition of superconductors

Chemical vapour deposition processes (CVD) can produce metastable fine-grained materials as well as epitaxial coatings and can have a very large throwing power depending on the process parameters. Therefore, CVD is an prospective method to deposit high-temperature superconducting materials withT _c⩾10 K. One of the first superconductors which were produced was Nb₃Sn on tapes and single wires. This superconducting material is, however, today produced by metallurgical methods. Since the detection of Nb₃Ge, CVD has become for these coatings the main method of production for the following reasons: high deposition rates, possibility to dope the material by addition of further doping gases to the CVD-process, continuous process. These coatings were deposited on tapes. For the first time the large throwing power of the CVD process was utilized for the deposition of B1 -NbC _x N _y , on carbon fibre bundles. This opens the possibility to produce multifilamentary structures used for magnetic applications. The structure of the coating can be varied by changing the gas properties, by addition of further gases, by an ultrasonic field, by ignition of a gas discharge and by multi-layering. CVD could also be a prospective method for producing the new class of superconductors withT _c⩾30 K.     

Chemical vapour deposition of coatings

Chemical Vapour Deposition (CVD) of films and coatings involve the chemical reactions of gaseous reactants on or near the vicinity of a heated substrate surface. This atomistic deposition method can provide highly pure materials with structural control at atomic or nanometer scale level. Moreover, it can produce single layer, multilayer, composite, nanostructured, and functionally graded coating materials with well controlled dimension and unique structure at low processing temperatures. Furthermore, the unique feature of CVD over other deposition techniques such as the non-line-of-sight-deposition capability has allowed the coating of complex shape engineering components and the fabrication of nano-devices, carbon-carbon (C-C) composites, ceramic matrix composite (CMCs), free standing shape components. The versatility of CVD had led to rapid growth and it has become one of the main processing methods for the deposition of thin films and coatings for a wide range of applications, including semiconductors (e.g. Si, Ge, Si_1-xGe_x, III-V, II-VI) for microelectronics, optoelectronics, energy conversion devices; dielectrics (e.g. SiO₂, AlN, Si₃N₄) for microelectronics; refractory ceramic materials (e.g. SiC, TiN, TiB₂, Al₂O₃, BN, MoSi₂, ZrO₂) used for hard coatings, protection against corrosion, oxidation or as diffusion barriers; metallic films (e.g. W, Mo, Al, Au, Cu, Pt) for microelectronics and for protective coatings; fibre production (e.g. B and SiC monofilament fibres) and fibre coating. This contribution aims to provide a brief overview of CVD of films and coatings. The fundamental aspects of CVD including process principle, deposition mechanism, reaction chemistry, thermodynamics, kinetics and transport phenomena will be presented. In addition, the practical aspects of CVD such as the CVD system and apparatus used, CVD process parameters, process control techniques, range of films synthesized, characterisation and co-relationships of structures and properties will be presented. The advantages and limitations of CVD will be discussed, and its applications will be briefly reviewed. The article will also review the development of CVD technologies based on different heating methods, and the type of precursor used which has led to different variants of CVD methods including thermally activated CVD, plasma enhanced CVD, photo-assisted CVD, atomic layer epitaxy process, metalorganic assisted CVD. There are also variants such as fluidised-bed CVD developed for coating powders; electrochemical vapour deposition for depositing dense films onto porous substrates; chemical vapour infiltration for the fabrication of C-C composites and CMCs through the deposition and densification of ceramic layers onto porous fibre preforms. The emerging cost-effective CVD-based techniques such as electrostatic-aerosol assisted CVD and flame assisted CVD will be highlighted. The scientific and technological significance of these different variants of CVD will be discussed and compared with other vapour processing techniques such as Physical Vapour Deposition.     

Chemical vapour deposition of silanes

Chemical surface modification of oxide-covered surfaces by silanization is a well-known technique in such fields as gas and liquid chromatography, electro-chemistry and immobilization of biomolecules. In the commonly used silanization technique the silane is reacted with the surfaces in a liquid phase. If strict anhydrous conditions do not prevail, however, this technique often results in polymerization, irreproducibility and instability of the silane films. We report here on a gas phase silanization of silicon surfaces at elevated temperatures. The method comprises a washing and surface activation step followed by silanization at about 0.5–1 Nm^?2 and 80–190 °C depending on the type of silane. The silanized surfaces were characterized by ellipsometry, contact angle measurements and scanning electron microscopy, which revealed smooth, stable and reproducible silane films of monolayer character. A comparison of surfaces that were silanized in the gas phase with those that were silanized in the liquid phase was also made.     

Chemical vapour deposition of chromium

The chemical vapour deposition of chromium and the partial transformation of chromium into chromium carbide on carbon-containing substrates such as tool steels was investigated.The process using CrCl₂ as the reactive gas is described. Of the different process parameters studied, the substrate composition was found to have an important influence on the nature and properties of the chromium layer. In the early stages of deposition the reaction is controlled by the exchange of Fe from the substrate for Cr. As the H₂ reduction process becomes increasingly important, a nearly linear relationship exists between the growth rate and the deposition time. The composition, structure, thickness, hardness, roughness, corrosion resistance and tribological properties of the coatings are described. Some applications of chromium coatings are also given.