Characterization of ZrO2 and SiC ceramic thin films prepared by electrostatic atomization

ZrO₂ and SiC ceramic thin films and their bilayer have been successfully prepared by a newly developed electrostatic atomization technique. This technique can generate fine spray of ceramic suspensions in a micrometer sized range with a narrow size distribution which is crucial for preparation of uniform thin films of these ceramic materials. Compared to some other thin film deposition techniques, such as Chemical vapour deposition (CVD), physical vapour deposition (PVD) and plasma spray (PS) etc. the thin film deposition process using electrostatic atomization is not only cheap but also controllable. The prepared ZrO₂ and SiC thin films were investigated using scanning electron microscopy (SEM) and energy dispersion analysis (EDA) techniques. These thin films were observed to be homogenous with a particle size less than 10 m. The ZrO₂-SiC bilayer was found to have an abrupt interface, implying that the deposition process is controllable and also that functionally graded ceramic/ceramic materials can be prepared in this way if the thickness of each layer is accurately controlled.     

The influence of Ni catalyst on the growth of carbon nanotubes on Si substrates

This article treats the influence of the treatment of a Ni catalyst upon the growth of carbon nanotubes in alcohol catalytic chemical vapour deposition (AC CVD) equipment. Prior to the growth of diamond, a thin film of Ni was deposited on a silicon substrate by magnetron sputtering. We observed that a combination of annealing of the Ni catalyst in vacuum and NH₃ had a positive effect upon the growth of carbon nanotubes (CNTs). The prepared CNTs were analysed by scanning electron microscopy and Raman spectroscopy.     

Growth of PbS and CdS thin films by low-pressure chemical vapour deposition using dithiocarbamates

Thin films of cadmium and lead sulphides grown by chemical vapour deposition (CVD) and remote plasma enhanced chemical vapour deposition (RPECVD) using dithiocarbamates as precursors were prepared on fused silica, sapphire, (111)Si and (111)InP substrates. These films were deposited in the temperature range 473–873 K. It was established that the activation energy of the CVD process is 191.5±1.5 kJ mol⁻¹. The structure of polycrystalline films was halenide for PbS and wurtzite for CdS. It was also found that r.f.-plasma activation of the gas phase decreases remarkably the growth temperature and orders the film structure. RPECVD sulphide films had a high degree of preferred orientation.     

Laser physico-chemical vapour deposition of cubic boron nitride thin films

A laser physico-chemical vapour deposition (LPCVD) technique was developed based on the interaction of an ultraviolet laser beam with a boron nitride target and borazine gas to synthesize cubic boron nitride (CBN) thin films on silicon substrates. The process involved a hybrid of pulsed laser ablation (PLA) of a solid HBN target and chemical vapour deposition (CVD) using borazine as a feed stock. The films were characterized with scanning electron microscopy, X-ray diffraction and infrared spectroscopy. Results indicate that the thin films consisted of almost single-crystalline CBN structures and that the film quality in terms of adherence, particulate density and smoothness was excellent. The purity and crystal structure of target material, laser beam wavelength and energy fluence were the key variables that controlled the film characteristics. In contrast to LPCVD, the conventional PLA method did not generate CBN films.     

Silicon surface passivation by hot-wire CVD Si thin films studied by in situ surface spectroscopy

Silicon thin films can provide an excellent surface passivation of crystalline silicon (c-Si) which is of importance for high efficiency heterojunction solar cells or diffused emitter solar cells with well-passivated rear surfaces. Hot-wire chemical vapor deposition (hot-wire CVD) is an attractive method to synthesize Si thin films for these applications as the method is ion-bombardment free yielding good quality films over a wide range of deposition rates. The properties of the interface between hot-wire CVD Si thin films and H-terminated c-Si substrates have been studied during film growth by three complementary in situ techniques. Spectroscopic ellipsometry has been used to determine the optical properties and thickness of the films, whereas information on the H-bonding modes and H-depth profile has been obtained by attenuated total reflection infrared spectroscopy. Second-harmonic generation (SHG), a nonlinear optical technique sensitive to surface and interface states, has been used to probe two-photon resonances related to modified Si-Si bonds at the interface. By correlating the observations with ex situ lifetime spectroscopy experiments the growth and surface passivation mechanism of the Si films are discussed.     

Nucleation and growth study of copper thin films on different substrates and wetting layers by metal-organic chemical vapour deposition

Chemical vapour deposition of copper thin films on different diffusion barrier/adhesion promoter layers have been studied. Copper thin films were grown in low pressure CVD reactor, using Cu(dpm)₂ as precursor and argon as carrier gas. Growth rates, film adhesion to the substrate, and surface morphology were studied in detail. Paper presented at the poster session of MRSI AGM VI, Kharagpur, 1995     

Modeling and visualization of polycrystalline thin film growth

A novel polycrystalline thin film growth simulator, FACET, has been developed. FACET is a multi-scale model with two major components: an atomic level one-dimensional kinetic lattice Monte Carlo (1D KLMC) model and a real time feature scale two-dimensional facet nucleation and growth model.

The 1D KLMC model has been developed to calculate inter-facet diffusion rates. By inputting the diffusion activation energies, the model will calculate the inter-facet atomic flux between {1 0 0}, {1 1 0}, and {1 1 1} facets of FCC materials at any temperature. The results of the 1D KLMC model have been verified by comparison with a full three-dimensional kinetic lattice Monte Carlo (3D KLMC) model.

The feature scale polycrystalline thin film nucleation and growth model is based on describing grains in terms of two-dimensional faceted surfaces and grain boundaries. The profile of the nuclei are described by crystallographically appropriate facets. The position and orientation of the nuclei can be randomly selected or preferred textures can be created. Growth rates are determined from different deposition fluxes and surface diffusion effects. Quantitative microstructural characterization tools, including roughness analysis, average grain size analysis, and orientation distribution analysis, were incorporated into the model, which allows the users to design, conduct and analyze the virtual experiments within one integrated graphical user interface. Users can also visualize the nucleation and growth process of the film and obtain the final film microstructure. The effects of thickness, temperature, and deposition flux on thin film microstructures have been studied by FACET.     

Electrochemical investigation and characterization of thin-film porosity

In thin-film applications it is necessary to control film properties such as homogeneity and porosity to obtain high-quality coatings. Electrochemistry can be a very helpful tool since it can provide information about processes taking place at the interface between substrate and coating. Different thin carbon-based coatings were deposited via physical vapour deposition methods and vapour phase polymerization on pure iron substrates: fullerene films, which were modified by an ion bombardment and thin films of poly(p-xylylene), which is a very good insulating polymer. The film porosity and stability of the film/substrate system against aqueous corrosion were investigated and compared using cyclic voltammetry. The dependence of porosity and film stability on various deposition process parameters such as film thickness and plasma conditions was measured via the dissolution current density and the open circuit potential shift of the substrate material. It could be shown that the two measurements, current density I_crit. and open circuit potential E_ocp. can provide useful complementary information about film porosity that can lead to a better understanding of the coatings properties and the deposition process as well.     

Effects of Ti- and Zr-based interlayer coatings on the hot filament chemical vapour deposition of diamond on high speed steel

The prospect of obtaining good adhesion of diamond films onto steel substrates is highly exciting because the achievement of this objective will open up applications in the cutting and drilling industry. However, a major problem with depositing diamond onto steel is high diffusion of carbon into steel at chemical vapour deposition (CVD) temperatures leading to very low nucleation density and cementite (Fe₃C) formation. Therefore, the study of the nucleation and growth processes is timely and will yield data that can be utilised to get a better understanding of how adhesion can be improved. This work focuses on investigating the adhesion of thin diamond films on high speed steel previously coated with various interlayers such as ZrN, ZrC, TiC and TiC/Ti(C,N)/TiN. The role of seeding on nucleation density and the effect of diamond film thickness on stress development and adhesion has been investigated using SEM, XRD and Raman spectroscopy.The main emphasis in this study is the TiC interlayer which for the first time proved to be a suitable layer for diamond CVD on high speed steel (HSS). In contrast from other interlayer materials investigated here, no delamination was observed even after 3 h of CVD at 650 °C only when TiC was employed. Nevertheless, the increase of diamond film thickness on TiC coated HSS substrates led to the delamination of small areas in various regions of the substrate. This occurrence suggests that there was a distribution of adhesive toughness values at the diamond/TiC interface with stress development being dependent on film thickness.     

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.     

Diagnostic in TCOs CVD processes by IR pyrometry

Infra red pyrometry is a sensitive, simple and low-cost technique commonly used for the measurement of the deposition temperature in CVD processes. We demonstrate in this work that this optical technique can be used as diagnostic tool to provide fruitful informations during the growth under atmospheric pressure of TiO₂ films on various substrates chosen as an example of transparent oxide. Significant variations of the pyrometric signal were observed during the deposition of TiO₂ thin films due to interferences in the growing film resulting from multi-reflections at the interfaces and scattering induced by the surface roughness. Modeling of the time dependence of the IR pyrometric signal allows simultaneously the determination of the layer thickness, the growth rate, surface roughness and refractive index of the thin films under the growth conditions. This diagnostic technique can be used for various transparent thin films grown on opaque substrates and is well adapted to control CVD processes operating either under atmospheric or low pressure and more generally any thermal treatment processes.     

Monte Carlo simulations of very low pressure chemical vapor deposition

Summary Simulation strategies for chemical vapor deposition (CVD) of thin solid films are presented, with emphasis on direct simulation Monte Carlo methods for analyzing and predicting physical phenomena occurring at low pressures and in micron-sized substrate features. The Monte Carlo approach is placed in perspective, relative to standard continuum mechanics-based strategies for modeling of CVD systems. Design issues that may be addressed through the developed methods are exemplified with computations for a new, technologically important CVD process for epitaxy of Si and Si_xGe_1-x alloys. Specifically, radiative heat transfer, rarefied gas-flow characteristics, species separation caused by pressure and thermal diffusion, growth-rate uniformity vs. surface reactivity, and deposition in microscopic features are addressed as parts of the overall CVD reactor-design approach. Process implications of rarefied transport effects unique to very low pressure CVD conditions are described. A new profile evolution technique is also introduced which predicts film topology, as well as the microstructure of the film.     

Contact damage evolution in a diamond-like carbon (DLC) coating on a stainless steel substrate

A diamond-like carbon thin film was coated onto a stainless steel substrate using plasma assisted chemical vapour deposition (PACVD). Instrumented indentation and scratching were used, supported by focused ion beam (FIB) microscopy, to explore deformation and fracture behaviours of this coating system. The formation and growth of ring and radial cracks in the coating, as well as plastic flow in the ductile substrate, were observed to be the predominant deformation processes for this coating system. Lateral cracking occurred at the interface of the coating/substrate following indentation, but in the middle of the coating following scratching. No evidence of plastic flow within the coating was observed. Coating deformation is, therefore, controlled by its fracture energy. An indentation-energy-based model was applied to evaluate the fracture toughness of the coating.     

Adhesion of diamond coatings on cemented carbides

Precise quantification of the adhesion of diamond coatings on cemented carbide (WC-Co) inserts is important for industrial applications. Adhesion is strongly influenced by the surface roughness, surface reactivity, catalytic effect of Co during diamond chemical vapour deposition (CVD) and by stresses developed in the film and at the bonding interface.

In this work we investigated the adhesion of diamond coatings on WC-Co by using Rockwell-C indentation. Various surface modifications were studied: Co leaching; replacement of Co by Cu; WC-Co decarburization and deposition of Ti intermediate layer prior to diamond CVD. Turning tests with diamond coated inserts for machining of Al alloy were carried out.     

IR spectra and etch rates of plasma-enhanced chemically vapour-deposited phosphosilicate glass films

IR transmission spectra of phosphosilicate glass (PSG) films with 8 wt.% P prepared by plasma-enhanced chemical vapour deposition (PECVD) and CVD are compared. The differential IR spectrum of a PECVD PSG film differs from that of a CVD PSG film: the P=O peak has a lower intensity than the corresponding peak of the CVD film with the same phosphorus content; no peaks are evident at 980 and 500 cm⁻¹—the characteristic frequencies for P---O---P stretching and bending vibrations. The differential IR spectra of PECVD and CVD PSG films become very similar after annealing for 4 h in water vapour at 850°C. The etch rate of a PECVD film in p-etchant, which is constant throughout the film thickness, is 400 Å min⁻¹. However, the etch rate recorded after the film is subjected to annealing in water vapour at 850°C varies with the depth in the film, attaining values as high as 800 Å min⁻¹ in the region near the outer surface of the film. The results are explained as due to the oxidation of P₂O₃ to P₂O₅.     

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.     

Diamond-like Carbon Film from Camphor Soot

Diamond-like carbon film (DLC) has been deposited from the soot of camphor, a natural source, by a simple vacuum deposition technique, for the first time. This method of deposition is simple, convenient and much faster than the conventional gas cracking technique usually adopted for the DLC film deposition. DLC thin film is characterized by Raman, FTIR, solid state ¹³C NMR, ESR and SEM. Preliminary results (XRD and SEM analyses) suggest that the polycrystalline diamond film may also be obtained from this source. The prime novelty of this work is that from the same source, we have been able to synthesize both DLC film as well as polycrystalline diamond film by a simple vacuum deposition technique without using any external gas like the conventional chemical vapour deposition (CVD) methods.     

Interface structure of deposited GaSb on GaAs (001): Monte Carlo simulation and experimental study

The growth of GaSb thin films by MBE on GaAs (001) is investigated experimentally, using TEM, and theoretically, using KMC simulations. The atomic scale mechanisms inherent to the growth are discussed and described in the KMC model in which the strain is introduced through an elastic energy term based on a valence force field approximation. We observe that the first two monolayers of the deposited films form strained three-dimensional clusters, but further deposition induces film relaxation and rough 3D growth with valley formation presenting (111) facets with unstable bottoms. We show that the roughening morphology and creation of grooves during growth are in agreement with experimental TEM observations.     

A low temperature process for the reactive formation of Si3N4 layers on InSb

Standard chemical vapour deposition (CVD) processes for the deposition of silicon nitride films require working temperatures of 275°C or above which are liable to cause surface degradation of III–V semiconductors such as InSb. In this paper, a room temperature CVD process yielding Si₃N₄ layers with electrical characteristics that are comparable with those obtained by conventional processes is presented. The film density and the adherence to the InSb substrates could be significantly improved using a special electrode configuration and an in situ sputter etch prior to film deposition.     

Estimation of vapour pressure and partial pressure of subliming compounds by low-pressure thermogravimetry

A method for the estimation of vapour pressure and partial pressure of subliming compounds under reduced pressure, using rising temperature thermogravimetry, is described in this paper. The method is based on our recently developed procedure to estimate the vapour pressure from ambient pressure thermogravimetric data using Langmuir equation. Using benzoic acid as the calibration standard, vapour pressure-temperature curves are calculated at 80, 160 and 1000 mbar for salicylic acid and vanadyl bis-2,4-pentanedionate, a precursor used for chemical vapour deposition of vanadium oxides. Using a modification of the Langmuir equation, the partial pressure of these materials at different total pressures is also determined as a function of temperature. Such data can be useful for the deposition of multi-metal oxide thin films or doped thin films by chemical vapour deposition (CVD).