Continuous hot-wire chemical vapor deposition on moving glass substrates

Hot Wire Chemical Vapor Deposition (HWCVD) is a very suitable technique for homogeneous deposition of thin films on continuously moving substrates in an in-line manufacturing system. This process is further aided by the fact that transport of insulating substrates (such as glass) during deposition can be easily arranged as the substrate is not part of the decomposition mechanism as in plasma enhanced CVD. Rigorous grounding of the moving substrates is not required, and no special care needs to be taken to make shields or liners equipotential planes. Moreover, as the creation of dust particles in the gas phase can be avoided, deposition could be undertaken with the substrates facing upward, thus further simplifying the mounting of the substrates. Amorphous as well as microcrystalline silicon thin films with device-quality properties have been achieved on moving substrates. The first p-i-n solar cells made with a 300-nm thick i-layer that was deposited on a linearly moving substrate already showed efficiencies of 6.4%, despite two air breaks that were needed in these tests.     

New application of Cat-CVD technology and recent status of industrial implementation

Recent progress in application of Cat-CVD (Hot Wire CVD) technology is overviewed, along with recent status of industrial implementation of this technology. Although the use of Cat-CVD technology in factories has not been open to the public, the technology appears to fit for the fabrication of ultra-high frequency devices of compound semiconductors, compound semiconductor lasers, solar cells, and formation of coating films for other devices. The issues for practical use of this technology are also discussed, together with promising future of this Cat-CVD technology.     

The influence of working gas on CVD diamond quality

The effect of the working gas pressure and its composition on diamond quality and particles size was investigated. The diamond layers were grown in Hot Filament Chemical Vapor Deposition (HF CVD) reactor. A methanol–hydrogen gas mixture was used as the precursor gas. The structure of these films was characterized by scanning electron microscopy (SEM) and micro-Raman spectroscopy. Typically, the diamond's crystallite size decreased with increasing pressure and increasing with methanol concentration. Additionally the admixture of non-diamond (sp²-hybridized carbon) phase also increased with increasing both of deposition pressure and of methanol concentration. It was observed that the deposition pressure has a weaker influence on diamond quality than the methanol concentration.     

Growth of diamond thin films by chemical vapour deposition

Deposition of diamond thin films on non-diamond substrates at low pressures (<760 torr) and low temperatures (<2000°C) by chemical vapour deposition (CVD) has been the subject of intense research in the last few years. The structural and the electrical properties of CVD diamond films grown on p-type 〈111〉 and high-resistivity (>100 kΩ-cm) 〈100〉 oriented silicon substrates by hot filament chemical vapour deposition technique are described in this review paper.     

Hot Wire CVD for thin film triple junction cells and for ultrafast deposition of the SiN passivation layer on polycrystalline Si solar cells

We present recent progress on hot-wire deposited thin film solar cells and applications of silicon nitride. The cell efficiency reached for μc-Si:H n-i-p solar cells on textured Ag/ZnO presently is 8.5%, in line with the state-of-the-art level for μc-Si:H n-i-p's for any method of deposition. Such cells, used in triple junction cells together with hot-wire deposited proto-Si:H and plasma-deposited SiGe:H, have reached 10.5% efficiency. The single junction μc-Si:H n-i-p cell is entirely stable under prolonged light soaking. The triple junction cell, including protocrystalline i-layers, is within 3% stable, due to the limited thicknesses of the two top cells. The application of SiN_x:H at a deposition rate of 3 nm/s to polycrystalline Si wafer solar cells has led to cells with 15.7% efficiency. We have also achieved record high deposition rates of 7.3 nm/s for transparent and dense SiN_x;H. Hot-wire SiN_x:H is likely to be the first large commercial application of the Hot Wire CVD (Cat-CVD) technology.     

Multi-phase structured silicon carbon nitride thin films prepared by hot-wire chemical vapour deposition

In this work, Silicon Carbon Nitride (Si-C-N) thin films were deposited by Hot Wire Chemical Vapour Deposition (HWCVD) technique from a gas mixture of silane (SiH₄), methane (CH₄) and nitrogen (N₂). Six sets of Si-C-N thin films were produced and studied. The component gas flow rate ratio (SiH₄:CH₄:N₂) was kept constant for all film samples. The total gas flow-rate (SiH₄ + CH₄ + N₂) was changed for each set of films resulting in different total gas pressure which represented the deposition pressure for each of these films ranging from 40 to 100 Pa. The effects of deposition pressure on the chemical bonding, elemental composition and optical properties of the Si-C-N were studied using Fourier transform infrared (FTIR) spectroscopy, Auger Electron Spectroscopy (AES) and optical transmission spectroscopy respectively. This work shows that the films are silicon rich and multi-phase in structure showing significant presence of hydrogenated amorphous silicon (a-Si:H) phase, amorphous silicon carbide (a-SiC), and amorphous silicon nitride (a-SiN) phases with Si-C being the most dominant. Below 85 Pa, carbon content is low, and the films are more a-Si:H like. At 85 Pa and above, the films become more Si-C like as carbon content is much higher and carbon incorporation influences the optical properties of the films. The properties clearly indicated that the films underwent a transition between two dominant phases and were dependent on pressure.     

金刚石薄膜的性质、制备及应用

金刚石有着优异的物理化学性质，化学气相沉积金刚石薄膜的研究受到研究人员和工业界的广泛关注。通过评述金刚石薄膜的性质、制备方法及应用等方面的研究成果，着重阐述化学气相沉积金刚石薄膜技术的基本原理，分析了各种沉积技术的优、缺点。结合对金刚石薄膜应用的讨论，分析了金刚石薄膜在工业应用中存在的问题和制备技术的发展方向。分析结果表明：MWCVD法是高速率、高质量、大面积沉积金刚石薄膜的首选方法；而提高金刚石的生长速度、降低生产成本等是进一步开发刚石薄膜工业化应用所需解决的主要问题。     

Preparation of II–VI and IV–VI semiconductor films for solar cells by the isovalent substitution technique with a CBD-made substrate

II–VI and IV–VI semiconductor films for solar cell applications, namely, CdTe, CdS, CdSe, PbS, PbSe and PbTe, can be prepared in a two-stage deposition process. In this work we illustrate the two-stage process to obtain PbTe and CdSe films from precursor oxide or hydroxide films deposited by chemical bath deposition (CBD). At the first stage, plumbonacrite Pb₁₀(CO₃)₆O(OH)₆ or cadmium oxide/hydroxide CdO₂/Cd(O₂)_0.88(OH)_0.24 films were deposited onto a glass substrate by CBD, using an ammonia-free low-temperature process in an alkaline aqueous solution with corresponding ion sources. Then, at the second stage, the obtained film was placed in a chemical vapor deposition (CVD) Hot Wall reactor with gas transportation, where it acted as a substrate in the reaction of isovalent substitution of Te or Se for the nonmetallic film component, thus forming PbTe and CdSe films. A nitrogen flux of 0.25 L/min was used as the transporting gas. The source temperature was adjusted between boiling (Tb) and melting point (Tm) to control the flux gas of the source. The substrate temperature was adjusted to improve film quality. Structural and optical investigation of the films proved their high quality, which determines the possibility of using them as solar cell elements, in particular, in multijunction cells.     

Deposition of new microcrystalline materials, μc-SiC, μc-GeC by HWCVD and solar cell applications

This paper describes at first the present status of solar cell efficiencies prepared by Hot Wire CVD (HW-CVD), and then preparation techniques of μc-3C(cubic)-SiC developed for innovative solar cell applications by using HW-CVD method are presented. For preparing μc-3C-SiC, monomethylsilane (MMS) and hydrogen were used for reactant gases. The high conductivity of 5 S/cm could be achieved for N doped n-type μc-3C-SiC. For p-type, as-grown Al-doped μc-3C-SiC films showed a relatively high resistivity, but on thermal annealing, the conductivity increased to the level of 1 × 10^− 2 S/cm. Monomethylgermane (MMG) and H₂ were used to prepare μc-GeC thin films. μc-GeC thin films with a carbon composition of about 7-8% showed a clear shift of absorption coefficient spectra by 0.44 eV, when compared to crystalline Ge. The pin solar cell structures in which all p,i,n layers consist of μc-SiC have been prepared for the first time. It was found that μc-3C-SiC and μc-GeC are the promising candidates as the next generation thin-film solar cell materials, but at present, the film quality is strictly limited by the residual impurity concentration of filament material Re.     

Tungsten thin-film deposition on a silicon wafer: The formation of silicides at W-Si interface

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 with plasmochemical action, and (3) magnetron deposition used for comparison purposes. It is shown that a nanometer tungsten silicide W₅Si₃ layer is formed at the tungsten-silicon interface only under gas-phase deposition. The effect of annealing on the specimen composition and surface resistance is investigated. It is shown that the formation and growth of a silicide WSi₂ layer commences at 700°C for CVD films and at above 750°C for films obtained with plasmochemical deposition; this results in a drastic increase in their electrical resistance. Under optimal conditions, tungsten films of 8 × 10 ?6 Ω cm resistivity are produced.     

The versatility of hot-filament activated chemical vapor deposition

In the field of activated chemical vapor deposition (CVD) of polycrystalline diamond films, hot-filament activation (HF-CVD) is widely used for applications where large deposition areas are needed or three-dimensional substrates have to be coated. We have developed processes for the deposition of conductive, boron-doped diamond films as well as for tribological crystalline diamond coatings on deposition areas up to 50 cm × 100 cm. Such multi-filament processes are used to produce diamond electrodes for advanced electrochemical processes or large batches of diamond-coated tools and parts, respectively. These processes demonstrate the high degree of uniformity and reproducibility of hot-filament CVD. The usability of hot-filament CVD for diamond deposition on three-dimensional substrates is well known for CVD diamond shaft tools. We also develop interior diamond coatings for drawing dies, nozzles, and thread guides.Hot-filament CVD also enables the deposition of diamond film modifications with tailored properties. In order to adjust the surface topography to specific applications, we apply processes for smooth, fine-grained or textured diamond films for cutting tools and tribological applications. Rough diamond is employed for grinding applications. Multilayers of fine-grained and coarse-grained diamond have been developed, showing increased shock resistance due to reduced crack propagation.Hot-filament CVD is also used for in situ deposition of carbide coatings and diamond-carbide composites, and the deposition of non-diamond, silicon-based films. These coatings are suitable as diffusion barriers and are also applied for adhesion and stress engineering and for semiconductor applications, respectively.     

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.     

Thermodynamic investigation of the MOCVD of copper films from<Emphasis Type="Italic">bis</Emphasis>(2,2,6,6-tetramethyl-3,5-heptadionato)copper(II)

Equilibrium concentrations of various condensed and gaseous phases have been thermodynamically calculated, using the free energy minimization criterion, for the metalorganic chemical vapour deposition (MOCVD) of copper films usingbis(2,2,6,6-tetramethyl-3,5-heptadionato)copper(II) as the precursor material. From among the many chemical species that may possibly result from the CVD process, only those expected on the basis of mass spectrometric analysis and chemical reasoning to be present at equilibrium, under different CVD conditions, are used in the thermodynamic calculations. The study predicts the deposition of pure, carbon-free copper in the inert atmosphere of argon as well as in the reactive hydrogen atmosphere, over a wide range of substrate temperatures and total reactor pressures. Thin films of copper, grown on SiO₂/Si(100) substrates from this metalorganic precursor by low pressure CVD have been characterized by XRD and AES. The experimentally determined composition of CVD-grown copper films is in reasonable agreement with that predicted by thermodynamic analysis.     

Composite films prepared by immersion deposition of manganese oxide in carbon nanotubes grown on graphite for supercapacitors

Manganese oxide/carbon nanotube (CNT) composite films on graphite were prepared by growing CNTs on the substrate using chemical vapor deposition (CVD), followed by immersion in an aqueous solution of potassium permanganate. The CVD growth created favorable conditions for deposition of the oxide on the electrode, and an aligned porous structure of the composite films, which originated from the CNT growth, could be managed. Electrochemical behaviors of the CNT and the composite films for supercapacitors were studied in 1 M Na₂SO₄ solution. While the oxide deposition in the CNT films was identified as contributing to capacitance enhancement, it was also found that a mild heat treatment could improve performance of the composite films.     

Preparation and characterization of TiC-coated molybdenum wall for the JT-60 reactor

In order to prepare a surface of low atomic number Z for the first wall of the JT-60 reactor, TiC-coated molybdenum wall components were developed using a new technique of plasma-assisted chemical vapour deposition, known as three-dimensional plasma chemical vapour deposition (TP CVD). Using this method components of various sizes can be coated with a TiC film 20 μm thick without causing recrystallization of the molybdenum substrate. The characteristics of the TiC films obtained by TP CVD did not seem to differ from those of TiC films obtained by conventional CVD or those of solid TiC (bulk) as far as the composition, structure and mechanical properties are concerned. The adhesion between the TiC film and the molybdenum substrate was found to be adequate even when the molybdenum was deformed or fused.     

CVD ZrO2‐Beschichtung von Fasern bei Normaldruck

Atmospheric pressure CVD of ZrO₂ on fibers Two different Chemical vapor deposition processes on fiberbundles (number of fibers a few thousand, diameter of the single fiber ≈10 µm) with zirconium dioxide at atmospheric pressure have been developed (AiF project 12783N): 1) ZrO₂ thin films on SiTiC fibers were grown by flame‐CVD using zirconium dipivaloylmethanate or acetylacetonate as precursors. The total deposition rate of 3·10^–5 mol·m^–2·s^–1 was achieved in a 4 cm long deposition zone. 2) In a new atmospheric pressure CVD process the deposition took place via hydrolysis of zirconium dipyvaloylmethanate in water vapor. The total deposition rate of 7·10^–6 mol·m^–2·s^–1 has been achieved in a 60 cm long pilot setup. This value allows to deposit continuously a 10 nm thick ZrO₂ films on fibers moving with velocity of 30 m/h. The deposition rate demonstrated in this work is the highest achieved so far for ZrO₂ CVD at atmospheric pressure.     

Electronic properties of low temperature microcrystalline silicon carbide prepared by Hot Wire CVD

Microcrystalline silicon carbide (μc-SiC) was prepared at low substrate temperatures using Hot Wire chemical vapor deposition (HWCVD). High crystalline volume fractions were achieved at high hydrogen dilution and high deposition pressure. Without intentional doping, such material shows high dark conductivity and high optical absorption below the band gap. The material prepared at low deposition pressure or low hydrogen dilution, on the other hand, shows much lower conductivity and sub-gap absorption, but high spin densities up to 5 × 10¹⁹ cm⁻³. This high absorption can be attributed to free carriers, different to μc-Si:H where a correlation between the sub-gap absorption and the spin density is observed.     

Thermal barrier coatings produced by chemical vapor deposition

Yttria stabilized zirconia (YSZ) can be employed as thermal barrier coatings (TBCs) on Ni-based super alloys in gas turbines and aircraft engines. The YSZ coatings have been fabricated by atmospheric plasma spraying or electron-beam physical vapor deposition. The increase in operation temperature of gas turbines demands another fabrication process to obtain high quality TBCs. Chemical vapor deposition (CVD) can be an alternative route to prepare TBCs due to excellent conformal coverage and columnar microstructure. This paper reviews the fabrication of YSZ films by conventional thermal CVD and plasma CVD intended for TBCs. A new laser CVD developed by our group with a high deposition rate of 660 μm h⁻¹ was also briefly introduced.     

Thermal barrier coatings produced by chemical vapor deposition

Yttria stabilized zirconia (YSZ) can be employed as thermal barrier coatings (TBCs) on Ni-based super alloys in gas turbines and aircraft engines. The YSZ coatings have been fabricated by atmospheric plasma spraying or electron-beam physical vapor deposition. The increase in operation temperature of gas turbines demands another fabrication process to obtain high quality TBCs. Chemical vapor deposition (CVD) can be an alternative route to prepare TBCs due to excellent conformal coverage and columnar microstructure. This paper reviews the fabrication of YSZ films by conventional thermal CVD and plasma CVD intended for TBCs. A new laser CVD developed by our group with a high deposition rate of 660 µμh^-1 was also briefly introduced.     

Photocatalytic TiO(2) deposition by chemical vapor deposition

Dip-coating, spray-coating or spin-coating methods for crystalline thin film deposition require post-annealing process at high temperature. Since chemical vapor deposition (CVD) process is capable of depositing high-quality thin films without post-annealing process for crystallization, CVD method was employed for the deposition of TiO(2) films on window glass substrates. Post-annealing at high temperature required for other deposition methods causes sodium ion diffusion into TiO(2) film from window glass, resulting in the degradation of photocatalytic efficiency. Anatase-structured TiO(2) thin films were deposited on window glass by CVD, and the photocatalytic dissociation rates of benzene with CVD-grown TiO(2) under UV exposure were characterized. As the TiO(2) film deposition temperature was increased, the (112)-preferred orientations were observed in the film. The (112)-preferred orientation of TiO(2) thin film resulted in a columnar structure with a larger surface area for benzene dissociation. Obviously, benzene dissociation rate was maximum when the degree of the (112) preferential orientation was maximum. It is clear that the thin film TiO(2) should be controlled to exhibit the preferred orientation for the optimum photocatalytic reaction rate. CVD method is an alternative for the deposition of photocatalytic TiO(2).