I.r. spectra resolution in fluorinated silicon nitride films

The broad I.r. Si-N band (700–1200 cm^–1) in fluorinated silicon nitride films has been resolved. I.r. spectra of the samples have been fitted using Gaussian curves centred in positions determined from the maxima of the negative second derivative of the digitized spectra. In silicon nitride films deposited by plasma-assisted chemical vapour deposition from SiH₄-NF₃-NH₃-N₂ gas mixtures-SiF_n radicals (n=1–3) incorporated in their structures have been detected. The relative concentrations of the different fluorine radicals present in the network depend on the NF₃ flow ratio used. As the flow ratio increases above 0.5, -SiF and-SiF₂ concentrations in the film reach the steady state. However, an appreciable increase in-SiF₃ and [-SiF₂-] _n concentrations has been observed.     

Characterization of boron nitride films deposited from BCl3-NH3-H2 mixtures in chemical vapour infiltration conditions

Boron nitride (BN) thin films deposited by isopressure and isothermal chemical vapour infiltration (ICVI) from BCl₃-NH₃-N₂ mixtures have been characterized from a physicochemical point of view as functions of both the deposition conditions and the destabilizing action of moisture. As-deposited (deposited at 773 K and post-treated at 1273 K), the BN films are turbostractic (d _{0 0 2}=0.36 nm, L _c=1.5 nm), have a low density (1.4 g cm^–3) and contain oxygen (about 20 at%). A first oxygen content (191.5 eV by XPS) is inserted in the films during the CVI step in relation to the hygroscopy of intermediate solid products and the quasi-equilibrium between the formation of BN and B₂O₃. A second oxygen content (192.5 eV) is due to the hydrolysis of BN by moisture which induces a very drastic transformation of BN. This destabilization affects both boron and nitrogen atoms and leads to the formation of ammonium borate hydrates. Different post-treatments have been investigated to stabilize the BN films and it appears that nitriding under ammonia is the most efficient.     

Deposition characteristics and properties of iron nitride films by CVD using organometallic compound

Iron nitride films were prepared by chemical vapour deposition from the gas mixture of Fe(C₅H₅)₂-NH₃-H₂-CO₂. The effects of deposition parameters on the deposition characteristics were investigated. Iron nitride films were deposited above 500 ° C and the films of -Fe₄N single phase were deposited above 700 ° C. At 700 ° C and under the total gas flow rate from 1 to 8 l min^–1, the deposition rate of the film may be controlled by the transport of Fe(C₅H₅)₂ molecules to the surface of the deposits. At 700 °C and under the total gas flow rate of 4 l min^–1, the phases and nitrogen contents of the films were determined bypNH₃/pH₂ ^3/2, the controlling factor of the nitrogen contents of the films. Decreasing of the total gas flow rate and increasingpCO₂ increased the nitrogen contents of the films and phases with higher nitrogen were deposited. On the other hand, increasingpFe(C₅H₅)₂ and the absence ofpCO₂ increases the carbon contents of the films, and the phase with a greater solubility in carbon, i.e. -Fe₂N, was codeposited with -Fe₄N. The saturation magnetization of the films deposited at 700 ° C was in good agreement with that reported for the bulk iron nitride, which depended not on the deposition conditions but on the nitrogen contents of the films.     

Properties of silicon nitride films prepared by plasma-enhanced chemical vapour deposition of SiH4-N2 mixtures

The refractive indices and IR absorption spectra are measured for silicon nitride films plasma deposited from SiH₄-N₂-H₂ gas mixtures. The composition of the film (N:Si ratio) is derived from the value of the refractive index and the concentration of bonded hydrogen as Si-H and N-H in the film is estimated from the absorption intensities in the IR spectrum. The optimum deposition conditions for giving excellent insulating silicon nitride films are confirmed to be same as the conditions for giving films with stoichoimetric composition and the lowest amount of incorporated hydrogen.     

Plasma assisted chemical vapour deposition of boron nitride coatings from using BCl3–N2–H2–Ar gas mixture

Boron Nitride coatings have been deposited by plasma-assisted chemical vapour deposition (PACVD) from BCl₃/N₂/H₂/Ar gas mixtures in a hot wall capacitively coupled radio-frequency (13.56 MHz) reactor. The nature of active species in the plasma during deposition was determined by Optical Emission Spectroscopy (OES) and Mass Spectrometry (MS). The plasma characterisation was performed as follows: first, an Ar/H₂ plasma was studied in order to understand the influence of molecular hydrogen in the discharge mixture. Then the two precursors N₂ and BCl₃ were added and the new gas mixture studied. Finally the deposition plasma was investigated. These characterisations were correlated to the microstructure and c-BN concentrations determined by Scanning Electron Microscopy (SEM) and Fourier Transformed Infrared Spectroscopy (FTIR).The study demonstrates the major role of atomic hydrogen on the possible mechanisms leading to BN deposition:—the introduction of hydrogen in Ar/N₂ controls the nature of the NH_x (from N to NH₃) species in the gas phase. These results are correlated to the relative amount of NH groups in the films,—by a modification of the excitation state of the plasma (n_e, T_e) the introduction of H₂ can increase the dissociation rate of the boron precursor BCl₃ and, reacting with chlorine, leads to the formation of HCl. This corresponds to an increase in the growth rate of the coatings.Finally, BN samples containing 5% of cubic phase were treated by Ar, Ar/H₂ and Ar/Cl₂ plasmas. These post treatments demonstrated that ion assisted preferential etching of h-BN by H or Cl atoms could be used to obtain large concentrations of c-BN coatings and possibly offer a new route for deposition of low stress cubic boron nitride.     

Structural evolution of boron nitride films grown on diamond buffer-layers

Boron nitride films on diamond buffer layers of varying grain size, surface roughness and crystallinity are deposited by the reaction of B₂H₆ and NH₃ in a mixture of H₂ and Ar via microwave plasma-assisted chemical vapor deposition. Various forms of boron nitride, including amorphous α-BN, hexagonal h-BN, turbostratic t-BN, rhombohedral r-BN, explosion E-BN, wurzitic w-BN and cubic c-BN, are detected in the BN films grown on different diamond buffer layers at varying distances from the interface of diamond and BN layers. The c-BN content in the BN films is inversely proportional to the surface roughness of the diamond buffer layers. Cubic boron nitride can directly grow on smooth nanocrystalline diamond films, while precursor layers consisting of various sp²-bonded BN phases are formed prior to the growth of c-BN film on rough microcrystalline diamond films.     

Properties of stannic oxide thin films produced from the SnCl4-H2O and SnCl4-H2O2 reaction systems

Transparent and conductive stannic oxide films were produced at the relatively low temperature of 250°C from the SnCl₄-H₂O and SnCl₄-H₂O₂ reaction systems by a chemical vapour deposition method. The films were not doped with impurities. Films formed from the first system are superior to those formed from the second with respect to electrical properties although they have a lower deposition rate at the same deposition temperature. The former system gives rise to films with resistivities in the range 10–10^-3 Ω cm between 250 and 400°C. The latter system produces films with resistivities in the range 10²–10^-2 Ω cm between 250 and 450°C. The electrical properties depend on the absorption of hydrogen peroxide as well as on the grain size, which depends on the deposition temperature and the reaction system. The spectral transmissivity for films 0.36–1.1 μm thick varies over the range 80–95% in the regions between 400 and 650 nm for both systems. Different reaction mechanisms take place in different temperature regions for both systems since there are two activation energies in the plot of deposition rate as a function of temperature.     

Synthesis of vertically aligned boron nitride nanosheets using CVD method

Boron nitride nanosheets (BNNSs) protruding from boron nitride (BN) films were synthesized on silicon substrates by chemical vapor deposition technique from a gas mixture of BCl₃–NH₃–H₂–N₂. Parts of the as-grown nanosheets were vertically aligned on the BN films. The morphology and structure of the synthesized BNNSs were characterized by scanning electron microscopy, transmission electron microscopy, and Fourier transformation infrared spectroscopy. The chemical composition was studied by energy dispersive spectroscopy and X-ray photoelectron spectroscopy. Cathodoluminescence spectra revealed that the product emitted strong UV light with a broad band ranging from 250 to 400 nm. Field-emission characteristic of the product shows a low turn-on field of 6.5 V μm^?1.     

Low temperature deposition of hexagonal BN films by chemical vapour deposition

Transparent hexagonal BN films were deposited onto copper substrates from the reactant gas BCl₃-NH₃-H₂ at temperatures in the range 250–700°C. The lowest deposition temperature of the films was about 250°C. The films deposited at temperatures below 450°C were unstable in moist atmosphere and devitrified; a 20%–30% decrease in weight was observed when these films were heated above 600°C in an argon atmosphere. In contrast, the films deposited at temperatures above 600°C were very stable, decreased in weight by 1%–2% on heating and were stable in air at temperatures below 750°C.     

Plasma-enhanced chemical vapour deposition of AlN coatings on graphite substrates

Graphite substrates have been covered with aluminium nitride (AlN) layers prepared by plasma-enhanced chemical vapour deposition from AlBr₃-N₂-H₂-Ar gas mixtures. The glow discharge (frequency, 13.56 MHz; power, 50–500 W) was generated by an r.f. induction coil. The graphite substrate mounted on a grounded graphite susceptor was inductively heated up to a temperature in the range 200–800 °C. The mass of the deposit per square centimetre was determined as a function of reaction time, total gas pressure, substrate temperature, r.f. power, gas flow velocity and AlBr₃ concentration. The morphology of the AlN layers was examined by scanning electron microscopy. Fine-grained polycrystalline AlN films were grown at 700 °C under a total pressure below 10 Torr. Translucent polycrystalline AlN films having a 〈001〉 preferred orientation were deposited at a total pressure in the range 10–40 Torr.     

Thermodynamic Modeling of BC x N y Chemical Vapor Deposition in the B–C–N–H System

Thermodynamic analysis of the chemical vapor deposition of BN-based films in the B–C–N–H system was carried out for reduced pressures (133 and 1.33 Pa) and a wide temperature range (300–1300 K). The results indicate that, using mixtures of trimethylamineborane, (CH₃)₃N · BH₃, with H₂, NH₃, or N₂, one can produce films of various compositions: from BN to mixtures of BN, carbon, and boron carbide.     

Thermodynamic evaluation of chemically vapour- deposited Si3N4 films prepared by nitradation of dichlorosilane

The chemical vapour deposition (CVD) of Si₃N₄ layers based on the nitridation of dichlorosilane (SiH₂Cl₂) is evaluated thermodynamically. A study of the Gibbs free energy as a function of the temperature shows that Si₃N₄ deposition from the SiH₂Cl₂-NH₃ system is favoured to a greater extent than that from the SiH₂Cl₂-N₂ system. A similar study of the CVD of silicon oxynitride layers by the concomitant oxidation (with O₂, N₂O or CO₂) and nitridation (with NH₃) of SiH₂Cl₂ shows that the reactions of SiH₂Cl₂ with O₂ and N₂O are thermodynamically more favoured than its reaction with NH₃. The reverse effect is obtained when CO₂ is used as the oxidizing agent. A thermodynamic analysis of the SiH₂Cl₂-NH₃ system was made by solving numerically a set of equations involving the partial pressure of each species and the equilibrium constants at the temperature under consideration. From these calculations we can predict the gas phase composition, the amount of deposit expected and the efficiency of the deposition under various experimental conditions.     

The effect of diluent gases on the growth behavior of CVD SiC films with temperature

Silicon carbide films have been grown onto graphite substrates by low pressure chemical vapor deposition using MTS (CH₃SiCl₃) as a source precursor and H₂ or N₂ as a diluent gas. The experiments were performed at fixed conditions of a flow rate of 100 sccm for each MTS and carrier gas, a flow rate of 300 sccm for diluent gas addition, and a total pressure of 5 torr. The effect of temperature from 900°C to 1350°C and the alteration of diluent gas species on the growth rate and structure of deposits have been studied. The experimental results showed that the deposition rate increased with increasing deposition temperature irrespective of diluent gases and reactant depletion effect increased especially at H₂ diluent gas ambient. At MTS-H₂ system, the deposition mechanism changed from chemical reaction to mass transfer controlled reaction with temperature. Otherwise, For MTS-H₂-N₂ system, surface chemical reaction controlled the growth process at whole deposition temperature ranges. For N₂ addition, surface morphology of leaf-like structure appeared, and for H₂, faceted structure at 1350°C. The observed features were involved by crystalline phase of -SiC and surface composition with different gas ambient.     

Deposition rates of titanium nitride plates prepared by chemical vapour deposition of TiCl4+NH3 system

Titanium nitride plates (TiN_x,x = 0.74–1.0, about 2 mm thick maximum) were prepared by chemical vapour deposition (CVD) using TiCI₄, NH₃ and H₂ as source gases. The effects of CVD conditions, i.e. gas molar ratio (m _N/Ti = NH₃/TiCI₄) and deposition temperature (T_dep), on deposition rates and surface morphology were examined, and the deposition mechanism of the CVD-TiN_x plates was discussed. The relationship between m_N/Ti and deposition rates showed a maximum peak at certainm _N/Ti, and this maximum peak shifted to lowerm _N/Ti with increasing_{T dep}. The activation energy for the formation of CVD-TiN_x plates was about 80 kJ mol^–1 in the lower temperature range. The decomposition reaction of NH₃ gas could be associated with the rate-controlling step. At higher temperatures, the diffusion process may be the rate-controlling step, and a large amount of powder (mainly NH₄Cl) was formed in the gas phase. The highest deposition rate obtained in the present work was 1.06×10^–7 ms^–1 (0.38 mmh^–1) atT _dep = 1773 K andm _N/Ti = 0.87.     

Plasma etching of virtually stress-free stacked silicon nitride films

Stacked silicon nitride films for use in manufacturing of surface micromachined membranes were deposited using custom made plasma-enhanced chemical vapor deposition instrument with silane (SiH₄) and ammonia (NH₃) gas mixture as deposition precursor. Deposition conditions were adjusted by varying substrate temperature and SiH₄ to NH₃ flow ratio and temperature to obtain the required stress related and electrical properties of the membranes. Transmission Fourier transformed infrared spectroscopy and scanning electron microscopy were used to investigate the chemical composition and morphology of the stacked film components. An increase in the SiH₄ to NH₃ flow ratio and a decrease in temperature resulted in a silicon-rich silicon nitride film, as well as an increased silicon oxide concentration. To avoid underetch and sidewall defects, the plasma power density during the plasma etching was changed from 0.5 W/cm² during the etching of both top and bottom layers in a stacked film, to 1.0 W/cm² during the etching of the middle both silicon and silicon oxide rich film. This resulted in an improved overall stacked film sidewall quality and reduced the unwanted underetch.     

Kinetics of the chemical bath deposition of ZnSe films

Thin films of ZnSe were obtained by chemical bath deposition from a solution containing ZnCl₂, hydrazine (NH₂)₂H₂O, NH₃, and Na₂SSeO₃. The influence of the concentration of the components and of the temperature on the growth rate was studied. A hypothesis for a ZnSe formation process is proposed. The technological parameters for the preparation of thin dense films of sphalerite structure with a high transparency in the solar spectrum region are defined.     

Influence of nitriding gases on the growth of boron nitride nanotubes

Boron nitride (BN) nanotubes of different sizes and tubular structures exhibit very different mechanical and chemical properties, as well as different applications. BN nanotubes of different sizes and nanostructures have been produced in different nitriding gases in a milling and annealing process, in which elemental boron powder was first milled in NH₃ for 150 h and subsequently annealed at 1,200 °C for 6 h. The influence of nitriding gases was investigated by using N₂, NH₃, N₂–H₂ mixture gases. A relatively slow nitriding reaction in NH₃ gas leaded to a 2D growth of BN (002) basal planes and the formation of thin BN nanotubes without the help of metal catalysts. Fast nitriding reactions occurred in N₂ or N₂–H₂ mixture gases, catalyzed by metal particles, resulted in 3D crystal growth and the formation of many large cylindrical and bamboo tubes.     

Preparation of FeN x -TiN films by CVD

FeN _x -TiN films were prepared on fused silica substrates by chemical vapour deposition from the gas mixture of Fe(C₅H₅)₂, TiCl₄, NH₃ and H₂ as starting materials under atmospheric pressure. FeN _x -TiN films were deposited above 500°C and the constituent phase was a mixed phase of FeN _x and TiN. The composition, deposition rate and saturation magnetization of FeN _x -TiN films deposited at 750°C were in good agreement with the estimation made by assuming that FeN _x and TiN phases were independently deposited.     

Diamond-like carbon films prepared from CH4-H2-H2O mixed gas using a microwave plasma

Diamond-like carbon films were synthesized on polished silicon substrates from CH₄-H₂-H₂O mixed gas using a microwave plasma technique. The film properties were studied. Their growth rate was several times as fast as that for CH₄-H₂ mixed gas under the same experimental conditions. The films have a large Vickers hardness (5000 to 6000 kg mm^–2), high electrical resistivity (10¹² to 10¹³ cm) and good optical transparency, especially in the infrared region. Low hydrogen and oxygen contents in the films were detected by secondary ion mass spectroscopy.     

Chemical vapour deposition of thin films of BN onto fused silica and sapphire

Thin films of BN were prepared by chemical vapour deposition onto fused silica and sapphire using the reaction of BCl₃ with NH₃. The temperature of the substrate was varied between 600 and 1100°C. Transparent and smooth films of BN were obtained on fused silica and sapphire at substrate temperatures of 1000–1100°C. The growth rate of the film on sapphire was about 1 μm h^?1, and the growth rate on fused silica was about one-half that on sapphire. The films were chemically inert and adherent to the substrate. The absorption of the BN film was measured at room temperature. In the near-UV region, the main absorption peak was at about 6.2 eV and a sharp drop occurred near 5.8 eV. The sharp drop is attributed to the direct band gap. The photoluminescence of the films was measured at room temperature by excitation with light of wavelength 254 nm. A broad emission with a peak near 360 nm was observed.