Preferred orientation of AlN plates prepared by chemical vapour deposition of AlCl3 + NH3 system

Aluminium nitride (AlN) plates about 1 mm thick (maximum) were prepared by chemical vapour deposition (CVD) at the maximum deposition rate of 430 nm s⁻¹ using AlCl₃, NH₃ and H₂ gases at deposition temperatures,T _dep, of 873–1473 K. The effects of deposition conditions on the preferred orientation, morphology and micro-structure were investigated. WhenT _dep was less than 1073 K, the resulting CVD AlN plates contained some impurity chlorine and the aluminium content exceed the nitrogen content. WhenT _dep exceeded 1173 K, no chlorine was detected, and the Al/N atomic ratio matched the stoichiometric value. The lattice parameters (a=0.311 nm,c=0.4979 nm) and density (3.26×10³ kgm⁻³) were in agreement with values reported previously. The crystal planes oriented parallel to the substrates changed from (1 1 ˉ2 0) to (1 0 ˉ1 0) to (0001) with increasing total gas pressure (P _tot) and decreasingT _dep. This tendency is discussed thermodynamically and is explained by the change of supersaturation in the gas phase.     

Morphology and preferred orientation of titanium nitride plates prepared by chemical vapour deposition

Thick titanium nitride (TiN _x ; x = 0.74–1.0) plates (up to 2 mm thick) were prepared by chemical vapour deposition using TiCl₄, NH₃ and H₂ as source gases at a total gas pressure, P _tot, of 4 kPa, deposition temperatures, T _dep, from 1373–1873 K, and NH₃/TiCl₄, m _N/Ti, gas molar ratio from 0.17–1.74. The effects of deposition conditions on morphology, preferred orientation and composition of CVD-TiN _x plates were investigated. Surface morphology changed from faceted to nodular texture with increasing m _N/Ti and T _dep. The faceted and nodular deposits showed columnar and shell-like fracture cross-sections, respectively. The composition (x = N/Ti) increased with increasing m _N/Ti and T _dep below m _N/Ti = 1.0, and was constant above m _N/Ti = 1.0. Three kinds of preferred orientations were observed: (100) orientation at low T _dep, (110) orientation at intermediate T _dep and low m _N/Ti, and (111) orientation at high T _dep and high m _N/Ti. This tendency is discussed thermodynamically, and explained as being due to changes in the degree of supersaturation in the gas phase.     

Crystalline carbon nitride films prepared by microwave plasma chemical vapour deposition

Crystalline carbon nitride films have been synthesized on Si (100) substrates by a microwave plasma chemical vapour deposition technique, using mixture of N₂, CH₄ and H₂ as precursor. Scanning electron microscopy shows that the films consisted of hexagonal bars, tetragonal bars, rhombohedral bars, in which the bigger bar is about 20 μm long and 6 μm wide. The X-ray photoelectron spectroscopy suggests that nitrogen and carbon in the films are bonded through hybridized sp² and sp³ configurations. The x-ray diffraction pattern indicates that the films are composed of α-, β-, pseudocubic and cubic C₃N₄ phase and an unidentified phase. Raman spectra also support the existence of α- and β-C₃N₄ phases. Vickers microhardness of about 41.9 GPa measured for the films.     

Structure and morphology of titanium nitride films deposited by laser-induced chemical vapour deposition

Results on the deposition of titanium nitride on AISI M2 tool steel-type substrates by pyrolytic laser chemical vapour deposition are reported. Spots of TiN were deposited from a gas mixture of TiCl₄, nitrogen and hydrogen using a continuous wave quasi-TEM_oo CO₂ laser beam. The morphology and the structure of the deposited material were investigated by optical microscopy, scanning electron microscopy and X-ray diffraction. The chemical composition was studied with a scanning electron microscope with an energy dispersive spectrometer, and with an electron probe microanalyser. The topography of the coating was analysed with a stylus profilometer and different thickness profiles were measured depending on the laser-power densities and irradiation times. The morphology of the films showed a strong dependence on the laser-power density, interaction time and partial pressure of TiCl₄.     

Preparation of titanium nitride coated powders by rotary powder bed chemical vapour deposition

Titanium nitride coated powders were prepared by rotary powder bed chemical vapour deposition (CVD) in which a powder in a rotary specimen cell was heated by infrared radiation in a reactant gas stream. Titanium powder covered with TiN or Ti₂N thin film was obtained by diffusion coating treatment of titanium particles (grain size 10 to 50 µm) at 900 to 1000°C and 0.5 to 1.0 atm for 60 min in a nitrogen stream. TiN was coated on to the surface of scaly graphite particles (grain size 30 to 100 µm or 100 to 1000 µm) as well as titanium particles by CVD in the reactant system TiCl₄-N₂-H₂ at 900° C and 1 atm for 40 min. The uniformity of the coating (composition and film thickness) and the dispersability of the coated particles were considerably promoted by rotating the powder bed at about 90 r.p.m. compared with nonrotary powder bed CVD.     

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.     

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.     

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.     

Hybrid plasma chemical vapour deposition of aluminium nitride from Al and NH3/N2 mixtures

Abstracts are not published in this journal This revised version was published online in November 2006 with corrections to the Cover Date.     

Deposition of crystalline C3N4 films via microwave plasma chemical vapour deposition

Crystalline carbon nitride films have been synthesized on polycrystalline Ni substrates by a microwave plasma chemical vapour deposition technique, using a mixture of N₂, CH₄ and H₂ as precursor. Scanning electron microscopy shows that the film consisted of perfect crystals of short and long hexagonal bars, tetragonal bars and irregular particles. From the X-ray photoelectron spectroscopy (XPS) data, a maximum N/C ratio of 1.0 was achieved in the films. The XPS spectra of the film typically showed three peaks in the C 1s core spectrum (centered at 284.78, 285.94, and 287.64 eV) and two peaks in the N 1s core level spectrum (centered at 398.35 and 400.01 eV). This indicates that there are two types of C–N bonds; N is bonded to sp²- or sp³-coordinated C atoms in the as-deposited film. The X-ray diffraction pattern indicates that the film is composed of α-, β-, pseudocubic, graphitic C₃N₄ and an unidentified phase. A series of intense sharp Raman peaks were observed in the range of 100–1500 cm^− 1. These peaks match well with the calculated Raman frequencies of α- and β-C₃N₄, revealing the formation of α- and β-C₃N₄ phase.     

Preparation of SiB4±x and SiB6 plates by chemical vapour deposition of SiCl4 + B2H6 system

SiB_4±x and SiB₆ plates were prepared by chemical vapour deposition (CVD) using SiCl₄, B₂H₆ and H₂ gases under the conditions of deposition temperatures (T _dep) from 1323–1773 K, total gas pressures (P _tot) from 4–40 kPa and B/Si source gas ratio (m _B/Si=2B₂H₆/SiCl₄) from 0.2–2.8. The effects of CVD conditions on the morphology, structure and composition of the deposits were examined. High-purity and high-density SiB_4±x and SiB₆ plates about 1 mm thick were obtained at the deposition rates of 71 and 47 nm s⁻¹, respectively. The lattice parameter, composition and density of CVD SiB_4±x plates were dependent on their non-stoichiometry. The lattice parameter,a, was 0.6325 nm, butc ranged from 1.262–1.271 nm.The B/Si atomic ratio ranged from 3.1–5.0, and the density ranged from 2.39–2.45×10³ kg m⁻³. The CVD SiB₆ plates showed constant values of lattice parameters (a=1.444 nm,b=1.828 nm,c=0.9915 nm), composition (B/Si=6.0) and density (2.42×10³ kg m⁻³), independent of CVD conditions.     

Amorphous silicon prepared by low pressure chemical vapour deposition

Amorphous silicon films, grown by low pressure chemical vapour deposition (LPCVD) in a hot-wall reactor at temperatures around and below 500°C and at pressures of 100 mTorr, were investigated using various characterization techniques, to look for possible differences between these films and films grown by LPCVD at higher temperatures and by atmospheric pressure CVD (APCVD). The emphasis was placed on morphological (scanning electron microscopy and X-ray diffraction) and physical characterization (optical absorption, reflectivity, resistivity, Hall mobility and photoconductivity), while the hydrogen profile was measured using the ¹⁵N technique. The results indicate physical properties that are quite different from those of other LPCVD and APCVD films, properties which cannot be obtained by a simple extrapolation from higher deposition temperatures and which deserve further detailed investigation.     

Some properties of mullite powders prepared by chemical vapour deposition

The sinterability of mullite (3Al₂O₃·2SiO₂) powder prepared by chemical vapour deposition was examined to improve the conditions for fabricating dense mullite ceramics. The starting powder contained not only mullite, but also a small amount of -Al₂O₃ (Al-Si spinel) and amorphous material. Although the compressed powder was fired at a temperature between 1550 and 1700 °C for 1, 3 and 5 h, the relative densities of the sintered compacts were limited to 90%: (i) due to the creation of pores/microcracks during the solid state reaction (1100–1350 °C), and (ii) due to restriction on the rearrangement of grains because the amount of liquid phase (1550–1700 °C) was insufficient. Calcination of the starting powder was effective for preparation of easily sinterable powder with homogeneous composition. When the compact formed by compressing the calcined powder at 1400 °C for 1 h was fired at 1650 °C for 3 h, the relative density was raised up to 97.2%; moreover, mullite was the only phase detected from the sintered compact. The sintered compact was composed of polyhedral grains with sizes of 1–2 m and elongated grains with long axes of 6 m.     

Grain growth of copper films prepared by chemical vapour deposition

Copper films having thickness 600 nm were prepared on TiN using chemical vapour deposition (CVD). The deposited films were annealed at various temperatures (350–550°C) in Ar and H₂(10%)-Ar ambients. The changes in the grain size of the films upon annealing were investigated. Annealing in an H₂(10%)-Ar ambient produced normal grain growth; annealing in an Ar ambient caused grain growth to stop at 550°C. The grain size followed a monomodal distribution and the mean size increased in proportion to the square root of the annealing time, indicating the curvature of the grain is the main driving force for grain growth. Upon annealing at 450°C for 30 min in an H₂(10%)-Ar ambient, the average grain size of the film increased from 122 nm to 219 nm, and the resistivity decreased from 2.35 μΩ cm to 2.12 μΩ cm at a film thickness of 600 nm. This revised version was published online in July 2006 with corrections to the Cover Date.     

High temperature evaporation characteristics of amorphous Si3N4-C composite prepared by chemical vapour deposition

Evaporation characteristics of amorphous Si₃N₄ and amorphous Si₃N₄-C composite (6 wt % C) prepared by the chemical vapour deposition (CVD) were investigated in the temperature range of 1400 to 1650°C in a vacuum of about 10^?6 torr. The weight loss due to the evaporation was linear with time for all the samples tested. Evaporation rate of the amorphous CVD-(Si₃N₄-C) composite was 50 to 70% of that for the amorphous CVD-Si₃ N4. The activation energy for evaporation, calculated from the temperature dependence of the evaporation rates, was about 160 kcal mol^?1 for both samples. The carbon dispersed in the amorphous CVD-(Si₃N₄-C) composite reacted at the time of heat-treatment with the amorphous Si₃N₄ matrix and formedβ-SiC particles. Theβ-SiC particles were found to be about 100 nm in diameter and connected each other to form a three-dimensional network structure.     

Aluminium nitride deposition on 4H-SiC by means of physical vapour deposition

190 nm thick aluminium nitride (AlN) with a dielectric constant of 8.8 was deposited by physical vapour deposition (PVD) on n- and p-type Si and n-type 4H-SiC samples. The Metal–Insulator–Semiconductor, MIS, structures were analysed by IV and CV techniques and 1.2 kV SiC diodes were used to evaluate leakage current before and after AlN deposition. The samples were prepared both with and without 5% HF dip after UV exposure, prior to the AlN deposition. Structural AlN analysis showed polycrystalline composition with a dominant [002] phase, a density of 3.27 g/cm³ and stochiometry of Al_0.4N_0.6. Surface pre-treatment did not have much influence on the IV characteristics of Si samples (breakdown field ∼3 MV/cm). However, the non-HF-etched sample is characterised by 2.5 times smaller CV hysteresis for the p-type sample at 100 kHz. The SiC MIS structures have a high leakage current, nevertheless a beneficial influence of UV irradiation is observed in the case of the non-HF-etched sample (soft breakdown field ∼3 MV/cm compared to ∼2 MV/cm for HF-etched sample). The diode reverse current was about 2 pA before UV irradiation and 4 and 600 pA after AlN deposition at room temperature and at 150 °C, respectively.     

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.