Reactive sputter deposition of titanium dioxide

The microstructural, optical and electrical properties of reactively sputtered TiO_x films have been examined at points along the reactive deposition hysteresis curve. The deposition process utilizes feedback control loops of the current and oxygen/argon flowrates for operation in the internal region of the hysteresis curve. The variations in the optical properties are well correlated to the process conditions and the microstructure. For thicknesses of 60–100 nm, the films are polycrystalline for low deposition/high oxygen flow rates, and become amorphous for high deposition/low oxygen flow rates. Electron diffraction ring patterns of the polycrystalline phase are best fit to the d-spacings of the rutile structure. The index of refraction at 550 nm for the rutile phase polycrystalline films (10 nm grain size) is 2.6, this falls to 2.4 as the films become amorphous, and rises to 2.5 as the films become oxygen substoichiometric. We find the variation of the optical band gap of TiO_x to be less than 1%, and is less indicative of chemical and/or microstructural changes than the extinction coefficient at higher energies in the visible. The index of extinction at 350 nm shows a minimum at the same point as the index of refraction at 550 nm. We find the indirect fit of Tauc to the index of extinction gives the most linear fit. Variations in the complex index of refraction are consistent with the processing of r.f. sputtered films from titania targets.     

The influence of iron on the preparation of silicon nitride from silica

The thermodynamics of carbothermal reduction and nitriding of silica in the temperature range 1200 to 1600° C have been evaluated and may be used to determine the conditions required to form silicon nitride, silicon oxynitride or silicon carbide. The products of reaction are, however, frequently dictated by kinetic rather than thermodynamic considerations and the presence of impurities in the silica and carbon reactants is especially important. α-silicon nitride has been prepared from high purity silica and carbon but under identical conditions of temperature and nitrogen pressure the chemistry of the process changes markedly when a small amount of iron is added to the reactants. Below 1320° C iron has no effect and pure α-silicon nitride is formed but with increasing temperature the proportion of silicon carbide in the product increases. Above 1550° C silicon carbide is the stable solid phase in the Si-C-O-N system at 1 atm pressure. The process chemistry has been investigated by high-temperature reaction studies and X-ray diffraction and reaction mechanisms are proposed on the basis of microstructural observations of reactants and products.     

Rotary powder bed chemical vapour deposition of titanium nitride on spherical iron powder

Titanium nitride (TiN) was coated on to spherical iron powder by the rotary powder bed chemical vapour deposition technique using a reactant gas of the TiCl₄-N₂-H₂ system. The dispersibility of the coated powder was significantly improved by the adsorption of the reactant gas on to the rotating particles during raising the temperature. Polycrystalline TiN film, having a columnar structure of a few micrometres was coated on to the iron powder, typically at a deposition temperature of 1000° C and at a treatment time of 80 min. The TiN-coated iron powder showed an oxidation resistance up to about 650° C.     

Background of the titanium nitride deposition

A qualitative reaction kinetics model is described for reactive magnetron deposition of TiN. According to the model the compound formation on the film surface is driven by the rate of nitrogen ions coming from the plasma. The plasma of a DC planar magnetron sputtering source has been investigated with a single Langmuir probe above the target at discharge currents of 0.5 A and 1 A, and pressures of 4, 1 and 0.7 Pa. The composition of the argon-nitrogen process gas with the ratio of about 3 : 1 was fixed due to preliminary mixing in a container. The plasma features, i.e. plasma potential, floating potential, electron temperature and electron density have been obtained from the probe curves. This plasma has a spatial structure with the plasma potential of −1.5 V to 2.5 V, floating potential of −20 V to −4 V, electron temperature of 10,000 K to 40,000 K and electron density of 2×10¹⁶\m³ to 15×10¹⁶\m³. The results predicted those process parameters, i.e. pressure, discharge current, bias voltage and position of the substrate, that provided large nitrogen ion bombardment on a substrate surface. Titanium nitride layer with golden colour has been deposited.     

Single- and dual-ion-beam sputter deposition of titanium oxide films

The optical properties and the surface morphologies of single-ion-beam sputtering (SIBS) and dual-ion-beam sputtering (DIBS) depositions of titanium oxide films are investigated and compared. In the DIBS process, the ion-assisted deposition by the voltage of a low ion beam ranged from 50 to 300 V at a 0% and 44% oxygen percentage. Cosputtering with materials of Si, SiO(2) (fused silica), and Al is also utilized in SIBS to improve amorphous-structure film. For the low-absorption and surface-roughness film, the optimum deposition condition of DIBS and postdeposition baking temperature for SIBS and DIBS are essential to the process.     

Deposition of titanium nitride films onto silicon by an ion beam assisted deposition method

Titanium nitride (TiN) films were deposited onto silicon wafers using an ion beam assisted deposition (IBAD) method with an electron cyclotron resonance (ECR) ion source for ionizing the nitrogen (N₂) gas under a condition of high nitrogen ion to titanium neutral ratio. The deposition rate of the TiN films was strongly dependent on the evaporation rate, d_Ti, of Ti metal and decreased with increasing nitrogen ion current. The deposition rate can be approximated as d=βd_Ti?_N2/{1/k+?_N2}−αI, where β, k and α are proportional constants, ?_N2 is the sum rate of neutral and ionized nitrogen impinging onto the substrate, and I is the nitrogen ion current.     

The effects of deposition variables on deposition rate in the chemical vapour deposition of silicon nitride

Amorphous Si₃N₄ was deposited by a chemical vapour deposition technique using an SiCl₄, NH₄₃ and H₂ gaseous mixture onto a silicon single crystal. The effects of deposition time, substrate temperature, gas flow rate, system pressure and partial pressure of reactant gases on the deposition rate were investigated. The metal-insulator-semiconductor (MIS) structure was fabricated by evaporating gold on Si₃N₄ to measure the charges stored in the interface between the insulator and silicon. The charges were determined for different deposition temperatures from capacitance-voltage plots. The experimental results indicate that the growth of Si₃N₄ is a thermally activated process in this experimental condition. It is calculated that the apparent activation energy is about 33 kcal mol^-1 below the deposition temperature of 1100 °C. The homogeneous reactions in the gas phase are promoted when the total pressure is increased. At pressures above 300 Torr, deposition rates are decreased because the reactant gases are depleted because of the homogeneous reaction. The charges stored in the MIS structure are found to be larger at lower deposition temperatures.     

Post deposition annealing temperature effect on silicon quantum dots embedded in silicon nitride dielectric multilayer prepared by hot-wire chemical vapor deposition

The preparations of the 20-period of a Si quantum dot (QD)/SiN_x multilayer in a hot-wire chemical vapor deposition (HWCVD) chamber is presented in this paper. The changes in the properties of Si-QDs after the post deposition annealing treatment are studied in detail. Alternate a-Si:H and SiN_x layers are grown in a single SiN_x deposition chamber by cracking SiH₄, and SiH₄ + NH₃, respectively at 250 °C. The as-deposited samples are annealed in the temperature range of 800 °C to 950 °C to grow Si-QDs. All the samples are characterized by confocal micro Raman, transmission electron microscope (TEM), and photoluminescence (PL) to study the changes in the film structures after the annealing treatment. The micro Raman analysis of the samples shows the frequency line shifting from 482 cm^− 1 to 500 cm^− 1 indicating the Si transition from an amorphous to a crystalline phase. The TEM micrograph inspection indicates the formation of Si-QDs of size 3 to 5 nm and a density of 5 × 10¹²/cm². The high resolution TEM micrographs show an agglomeration of Si-QDs with an increase in the annealing temperature. The PL spectra show a peak shifting from 459 nm to 532 nm with increasing the annealing temperature of the film.     

Characterization of titanium nitride films deposited onto silicon

Films of titanium nitride were prepared by reactive evaporation and r.f. sputtering and were characterized from the optical, electrical, and chemical and structural points of view. The effect of oxygen, introduced during the deposition process as well as in a subsequent thermal annealing, on the properties of the films is reported. The applicability of titanium nitride to silicon solar cells as a transparent conducting material is briefly discussed.     

Chemical vapour deposition of titanium nitride on plasma nitrided steel

Ferritic and austenitic nitriding by the plasma nitriding technique were investigated for the modification of steel substrates prior to the chemical vapour deposition of titanium nitride at 1273 K. It was confirmed that prenitriding enhances the growth of the titanium nitride layer and it was found that a TiN coating can be formed using substrate derived nitrogen only. Control of porosity, arising during austenitic nitriding, was investigated and it was found that in practice this phenomenon could not be avoided.     

Nitrogen pulsing to modify the properties of titanium nitride thin films sputter deposited

TiN _x thin films were grown on (100) Si and glass substrates by dc reactive magnetron sputtering. A titanium target was sputtered in Ar + N₂ atmosphere using a pulsing flow rate of the nitrogen gas. A constant pulsing period was used for every deposition whereas the nitrogen injection time was changed. The systematic variation of the nitrogen injection time led to a gradual decrease of the deposition rate and to a controlled modulation of the chemical composition of the TiN _x films (x between 0 and 1.05). Analysis of the crystallographic structure by X-ray diffraction showed that both Ti and TiN phases coexisted and a change of the preferential orientation from (200) to (111) occurred. The electrical conductivity and colour measurements in the CIE-L*a*b* system of colourimetry were also performed and correlated with the evolution of the N/Ti ratio.     

Analysis of coating interlayer between silicon nitride cutting tools and titanium carbide and titanium nitride coatings

Silicon nitride (Si₃N₄) cutting tools exhibit excellent thermal stability and wear resistance in the high-speed machining of cast irons, but show poor chemical wear resistance in the machining of steel. Conventional chemical vapour deposition (CVD) coating of Si₃N₄ tools has not been very successful because of thermal expansion mismatch between coatings and the substrate. This problem was overcome by developing a CVD process to tailor the interface for titanium carbide (TiC) and titanium nitride (TiN) coatings. Computer modelling of the CVD process was done to predict which phases would form at the interface, and the results compared with analyses of the interface. Three Si₃N₄ compositions were considered, including pure Si₃N₄, Si₃N₄ with a glass phase binder, and Si₃N₄ + TiC composite with a glass phase binder. Results of machining tests on coated tools show that the formation of an interlayer provides superior wear resistance and tool life in the machining of steel as compared to uncoated and conventionally coated Si₃N₄ tools.     

Effect of substrate temperature and deposited thickness on the formation of iron silicide prepared by ion beam sputter deposition

Ion beam sputter deposition (IBSD) method was employed to find optimum conditions for the formation of epitaxial β-FeSi₂ films on Si(100) substrate. It was found that crystal structure of the films as determined by X-ray diffraction (XRD) analysis is dependent on the substrate temperature as well as on the deposited thickness of sputtered Fe. The film with best crystal properties was obtained either at 873 K with the deposited Fe thickness of 15 nm, or at 973 K with the deposited Fe thickness of 30 nm. The obtained results indicate the importance of Fe and/or Si diffusion in determining the crystal properties of β-FeSi₂ film.     

Chemical vapor deposition of titanium nitride at low temperatures

A new method is proposed for making titanium nitride (TiN) films at substrate temperatures between about 400 and 700°C. The films are formed from TiCl₄ and NH₃ by chemical vapor deposition. The method is versatile with growth rates of up to 0.1 μm s⁻¹ possible. The optical properties of the films are measured and fitted theoretically using the Drude theory to obtain the plasma frequency of the films. A modification of the Drude theory according to Maxwell Garnett explains a decreased reflectance in the IR region for the thinner films. Use of the films as heat mirrors and other applications are discussed.     

Mixed-mode high temperature toughness of silicon nitride

Both opening-mode and mixed-mode fracture toughness tests were carried out at 1200 and 1300 °C on a sinter/HIP grade of silicon nitride. Data for pure opening loading (K _Ic) agree well with other experiments on the same material, which showed that the toughness was lower at 1000 °C than at room temperature, but increased as temperature increased above 1000 °C. The ratio of K _IIc/K _Ic was sufficiently insensitive to temperature that it can be considered to be constant. Results are discussed in the context of mechanisms that have been proposed to explain fracture toughness in silicon nitride.     

Study of titanium nitride deposition by supersonic plasma spraying

In this study, titanium nitride (TiN) deposition by reactive spraying was carried out under a low-pressure environment using a DC arc plasma jet generator with a supersonic expansion nozzle. Titanium powders were injected using a hollow cathode with argon gas, and nitrogen or nitrogen and hydrogen mixture was used as the plasma gas. Microstructure and properties of the coatings were examined using scanning electron microscope and X-ray diffraction. A dense TiN coating with a Vickers hardness of 2000 Hv was formed at a substrate temperature of 700 °C with a low input power of 5.3 kW. The results showed that the supersonic plasma jet in thermodynamic and chemical nonequilibrium state exhibits high potentials for reactive spraying.     

Chacterization of titanium silicon nitride films deposited by PVD

In recent years, nitride coatings have found widespread applications for tool and other hard surfaces. In this work, the (Ti,Si)N system was investigated and some of its properties characterised. For this, (Ti,Si)N films with thicknesses ranging from 1 to 3.3 μm and different contents of Ti and Si were deposited onto silicon wafers and polished high-speed steel substrates by r.f. reactive magnetron sputtering technique. The atomic composition of the samples were measured by Rutherford Backscattering Spectrometry (RBS). Ti_1−xSi_xN samples with 0≤x≤0.37 were produced. With regard to the structural properties, two cubic crystallographic structures were found, with lattice parameters of about a=4.29 Å and 4.18 Å. The grain size, evaluated by Fourier analysis of X-ray peaks, ranged from 5 nm to 34 nm. Comparing the adhesion results, the Ti_0.70Si_0.30N and Ti_0.83Si_0.17N sample presented the best results in adhesion with a critical load for total failure around 115 N and 105 N, respectively.     

The influence of preceramic binders on the microstructural development of silicon nitride

A number of polymeric precursors to silicon nitride were prepared and evaluated as binders in cold pressing/pressureless sintering operations. These polymers exhibited ceramic yields in excess of 75% by weight, and powder compacts made using them as binders displayed improved green handling properties. Compacts pyrolysed at 800 °C exhibited unusual microstructures, including the development of whiskers in situ. Based on microstructural observation, compacts sintered under pressureless conditions appeared to show enhanced densification relative to those processed without preceramic binders. Preceramic binders appeared to enhance the formation of -Si₃N₄ and may enhance densification of compacts sintered under pressureless conditions.