A nanoindentation study of thick cBN films prepared by chemical vapor deposition

The mechanical properties of high-quality cubic boron nitride (cBN) films were systematically investigated by nanoindentation measurements performed in both cross-sectional and plan-view directions. The large film thickness (∼5 μm) allows the effective ruling out of both substrate and indenter size effects. The hardness and elastic modulus values were found to be 70 and 800 GPa, respectively, which are the highest values ever obtained on cBN films deposited by either PVD or CVD methods so far (comparable to those reported for cBN crystals synthesized by high-pressure high-temperature methods). The variation of hardness across the cBN film thickness was investigated. In conjunction with the transmission electron microscopic observations, the relationship of the hardness measured with the crystallinity and crystal size/grain boundaries was discussed.     

Electrical and optical properties of titanium nitride coatings prepared by atmospheric pressure chemical vapor deposition

In order to examine the possibility for TiN coatings to be low-E, TiN coatings were deposited on the glass substrates by atmospheric pressure chemical vapor deposition using titanium tetrachloride (TiCl₄) and ammonia (NH₃) as precursors. X-ray diffraction, sheet resistance measurement, optical transmittance spectroscopy and infrared reflectance spectroscopy were carried out to determine the relationships between the preparation parameters and the microstructure, electrical and optical properties of the coatings. The results showed that the concentration of crystals increased with increasing the substrate temperature and the flow of TiCl₄, resulting in a decrease of the electrical resistivity. The optical transmittance of TiN thin films was strongly dependent on the gas flow and the substrate temperature. Under optimum conditions, continuous polycrystalline TiN coatings with FCC structure were obtained with an electrical conductivity around 34.5 Ω/□, an optical transmittance around 50% in the visible range, and an infrared reflectance higher than 50% above 3000 nm. This indicates that TiN coated glasses may be possible candidates for high IR reflectance windows.     

Properties of hydrogenated amorphous silicon prepared by chemical vapor deposition

Properties of hydrogenated amorphous silicon (a-Si:H) prepared by chemical vapor deposition (CVD) are reported and compared to corresponding properties of glow discharge a-Si:H. The CVD material was produced from mixtures of silane, disilane, trisilane and higher polysilanes in hydrogen carrier gas at one atmosphere total pressure, at substrate temperatures from 420 to 530 °C. The photovoltaic properties of our present CVD a-Si:H are somewhat inferior to those of the best glow discharge a-Si:H. However, as discussed below, there are some indications that higher quality CVD a-Si:H may be possible.     

Low-pressure chemical vapor deposition of TaCN films by pyrolysis of ethylamido-tantalum

Thin films of Tantalum nitride (TaN) were deposited from tetra-ethylamido-tantalum (Ta (NEt₂)₄) by low-pressure chemical vapor deposition. Good-quality step coverage is achieved below 400°C, because the deposition rate is determined by the reaction rates on the surface. The film resistivity increases, however, as the substrate temperature decreases. In order to obtain the low resistivity of films deposited at lower temperatures, we have increased the amount of injected H₂ gas during the deposition. The resistivity decreases by the increase in the H₂ gas flow rate, and it is shown that a large amount of H₂ gas injection during the deposition is an effective method for obtaining both low resistivity and high-quality step coverage. The residual carbon concentration in the film is measured to be >10%, on the other hand, the concentration of N less than 1%. The microstructural investigation using transmission electron microscopy (TEM) reveals that crystalline structure of the deposited film has an amorphous phase.     

A new model for low pressure chemical vapor deposition of SiO2 films by ozone augmented tetraethoxysilane

A simple model has been developed to analyze the low pressure chemical vapor deposition (LPCVD) of SiO₂ films from tetraethoxysilane (TEOS) and ozone. It is found that the model correlates well the experimental data taken at 30 to 90 Torr which is the range of the Applied Materials 5000 reactor. The model shows from correlations of experimental data that gas phase reaction reduces the deposition rate and that this effect becomes more significant at temperatures above about 365°C. The model also explains successfully the trend in experimental data on Arrhenius plots for pressures from 30 to 90 Torr. These data indicate that the temperature, T_m, at which the deposition rate is a maximum, decreases as the pressure is increased. This occurs because the effect of parasitic gas phase reactions becomes more important at higher pressure. Furthermore, thetrends predicted buy our model are consistent with the experimental data taken under atmospheric pressure chemical vapor deposition (APCVD), even though these conditions are outside the range of applicability of this model which assumes low pressure and therefore very high rates of diffusion.     

Homogeneous chemical vapor deposition of amorphous semiconductor thin films

In this paper we discuss the properties of amorphous hydrogenated silicon and germanium films prepared by homogeneous chemical vapor deposition. Emphasis is placed upon the important differences between HOMOCVD and plasma-deposited films. Experiments and calculations are presented which illustrate the most important reactor dynamical parameters.     

Plasma enhanced chemical vapor deposition of ZnO thin films

Zinc oxide thin films were deposited on silicon and corning-7059 glass substrates by plasma enhanced chemical vapor deposition at different substrate temperatures ranging from 36 to 400 °C and with different gas flow rates. Diethylzinc as the source precursor, H₂O as oxidizer and argon as carrier gas were used for the preparation of ZnO films. Structural and optical properties of these films were investigated using X-ray diffraction, reflection high energy electron diffraction, atomic force microscopy and photoluminescence. Highly oriented films with (0 0 2) preferred planes were obtained on silicon kept at 300 °C with 50 ml/min flow rate of diethylzinc without any post annealing. Reflection high energy electron diffraction pattern also showed the crystalline nature of these films. A textured surface with rms roughness ∼28 nm was observed by atomic force microscopy for the films deposited at 300 °C. A sharp peak at 380 nm in the PL spectra indicated the UV band-edge emission.     

Zinc oxide quantum dots embedded films by metal organic chemical vapor deposition

Zinc oxide (ZnO) quantum dots (QDs) were fabricated on silicon substrates by metal organic chemical vapor deposition. Formation of QDs is due to the vigorous reaction of the precursors when a large amount of precursors was introduced during the growth. The size of the QDs ranged from 3 to 12 nm, which was estimated by high-resolution transmission electron microscopy. The photoluminescence measured at 80 K showed that the emission of QDs embedded film ranged from 3.0 to 3.6 eV. The broad near-band-edge emission was due to the quantum confinement effect of the QDs.     

Metalorganic chemical vapor deposition of mesoporous SiTiOC nanostructured thin films

SiTiOC mesoporous thin films have been obtained by metalorganic chemical vapor deposition (MOCVD) using titanium iso-propoxide (TIP) and tetraethylorthosilicate (TEOS) as starting precursors. The influences of both carrier gas and deposition temperature on the properties of the produced films were extensively studied. The low-angle XRD analysis confirms that, all produced films under different conditions (gas type and temperature) have the mesoporous structure. However, the deposition temperature was found to be much effective in controlling both morphology and composition of the final films than the type of carrier gas. The morphology of the produced films was totally converted from spherical shape-like nanoparticles at 700 °C to lengthy at higher temperature of 1000 °C. The SEM-EDX investigations proved that the composition of the produced films was composed of SiTiOC structure system. The PL analysis has demonstrated along with FT-IR data that all the deposited films at various deposition parameters were composed mainly of SiO₂, SiOC, SiC, TiO₂ and TiOC bond structures and most probably nanocomposite SiTiOC system thin films.     

Formation of needlelike crystallites during growth of diamond films by chemical vapor deposition

Diamond polycrystalline films have been grown by chemical vapor deposition from a hydrogenmethane mixture. The phase composition and structure of the films were studied using Raman spectroscopy, electron microscopy, and thermogravimetry. It is found that, upon heating in air, the oxidation of the carbon material forming the films occurs at significantly different temperatures, depending on the degree of its order and the crystallite size. This difference is used for selective oxidation of the least ordered fine-grained component of the films. The material obtained by this selective oxidation of the films consists of diamond crystallites shaped like regular micrometer-sized tetragonal pyramids with a radius of tip curvature of several nanometers.     

Zn-doped AlInAs grown at high temperature by metalorganic chemical vapor deposition

Zn-doped AlInAs growth at high temperature, mainly at 750°C, by metalorganic chemical vapor deposition is investigated. When introducing DEZn during AlInAs growth, it is necessary to increase the TMAl flow rate in order to make the layer lattice-matched to InP. This is due to the enhanced In incorporation rather than the large covalent radius of Zn. To clarify the electrical characteristics, the dependence of the DEZn flow rate, the V/III ratio, and the growth temperature are investigated using the van der Pauw Hall method. In our growth system, a GaInAs intermediate layer is effective in preventing n-type inversion in Zn-doped AlInAs, which occurs when it is grown directly on an InP buffer layer. In addition, a large DEZn flow rate is effective for reducing carrier compensation in Zn-doped AlInAs layers grown at 750°C. Si impurities are apparently the cause of the type-inversion and compensation in Zn-doped AlInAs.     

Microstructure of hydrogenated silicon carbide thin films prepared by chemical vapour deposition techniques

We present the results of investigations on a variety of stoichiometric μc-SiC:H films deposited by Hot-Wire- and Plasma-Enhanced Chemical Vapour Deposition using monomethylsilane diluted in hydrogen as precursor gas. Infrared spectroscopy, grazing incidence X-ray diffraction, and Transmission Electron Microscopy were applied and compared to separate the contributions from the different structure phases of the material. It is shown that an evaluation of the crystalline volume fraction from the infrared absorption lineshape of the Si–C stretching mode is not possible, although stated in the literature. A correlation of this lineshape with the material strain is proposed. Moreover, a variation in strain, grain size, and structural defects is found depending on the deposition conditions, but a mixture of an amorphous and a crystalline phase could not unambiguously be identified.     

Smooth diamond films grown by hot filament chemical vapor deposition on positively biased silicon substrates

Smooth diamond films have been grown by hot filament chemical vapor deposition under DC bias on mirror-polished Si(100) substrates. Films of a few micrometers thickness were obtained in 30 min. The films were found to have d-spacing at 2.06 and 2.11 Å by X-ray diffraction. Raman spectra showed very broad peaks at 1329 (1336) and 1591 cm^-1. The films have a high density of planar defects and large internal stresses.     

Growth behavior of CuPc films by physical vapor deposition

Various Cu‐phthalocyanine (CuPc) films were grown from physical vapor deposition on top of indium‐tin‐oxide glass substrates by controlling substrate temperature (T_sub), source temperature (T_sou), and growth time. From side‐view SEM pictures, the growth rates for these CuPc films are estimated and can be categorized into three regions. From the Arrhenius plot of growth rate versus 1/T_sub, the activation energy E_A can be obtained. As T_sou = 390 °C, for region (A) with T_sub < 140 °C, the growth of CuPc films is dominated by the adhesion process with E_A = 810 meV. For region (B) with 140 °C < T_sub < 320 °C, the growth is then limited by the steric character associated with the organic molecular solids with E_A = 740 meV. For region (C) with T_sub > 320 °C, the re‐evaporation of the CuPc adhered molecules from the interface becomes dominant. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Effect of heat treatment on phase transformation of aluminum nitride ultrafine powder prepared by chemical vapor deposition

Ultrafine aluminum nitride (AlN) powders were obtained by chemical vapor deposition via AlCl₃–NH₃–N₂ system operated at various temperatures and at a same 200 cm³/min flow rate of NH₃ and N₂, respectively. It has been shown that when the reaction temperature of AlCl₃ and NH₃ was above 600°C, then crystalline AlN powder can be formed; whereas, amorphous AlN was obtained with NH₄Cl if reacted in a lower-temperature zone of the reaction chamber. The amorphous AlN powder was heat treated at 1400°C under NH₃ and N₂ atmosphere for 2 h, then the crystalline phases of the obtained powder belong to a single phase of AlN; a mixture of AlN and Al₂O₃ and only AlON, respectively. On the other hand, if crystalline AlN powder is heat treated at 1400°C under N₂ atmosphere for 2 h, the crystalline phases were composed of the major phase of AlN and a minor phase of Al₂O₃. The morphology, particle size and agglomerate size of the AlN powder were strongly dependent on the heat-treatment temperature. The particle size of AlN powder increases from 28.1 to 45.0 nm, as the heat treatment temperature increases from 800 to 1400°C.     

Effects of growth temperature on the properties of ZnO/GaAs prepared by metalorganic chemical vapor deposition

A series of ZnO films were grown on GaAs(0 0 1) substrates at different growth temperatures in the range 250–720°C by metalorganic chemical vapor depostion. Field emission scanning electron microscopy was utilized to investigate the surface morphology of ZnO films. The crystallinity of ZnO films was investigated by the double-crystal X-ray diffractometry. The optical and electrical properties of ZnO films were also investigated using room-temperature photoluminescence and Hall measurements. Arrhenius plots of the growth rate versus reciprocal temperature revealed the kinetically limited growth behavior depending on the growth temperature. It was found that the surface morphology, structural, optical and electrical properties of the films were improved with increasing growth temperature to 650°C. All the properties of the film grown at 720°C were degraded due to the decomposition of ZnO film.     

Noncatalytic synthesis of carbon nanotubes by chemical vapor deposition

A new method is proposed to obtain uniform arrays of multiwall carbon nanotubes without catalysts. Nanotubes have been formed by carbon condensation from a hydrogen-methane gas mixture activated by a dc discharge. Structural and morphological investigations of the obtained material were performed by Raman spectroscopy, scanning and transmission electron microscopy, energy-dispersive X-ray analysis, and electron energy loss spectroscopy. It is shown that the obtained nanotubes contain no impurities that could act as catalysts. Based on these experimental data, it is concluded that the nanotube synthesis under study is noncatalytic. Possible mechanisms of this synthesis are considered.     

Low-temperature deposition of crystalline silicon nitride nanoparticles by hot-wire chemical vapor deposition

The nanocrystalline alpha silicon nitride (α-Si₃N₄) was deposited on a silicon substrate by hot-wire chemical vapor deposition at the substrate temperature of 700 °C under 4 and 40 Torr at the wire temperatures of 1430 and 1730 °C, with a gas mixture of SiH₄ and NH₃. The size and density of crystalline nanoparticles on the substrate increased with increasing wire temperature. With increasing reactor pressure, the crystallinity of α-Si₃N₄ nanoparticles increased, but the deposition rate decreased.     

Tetragonal tungsten oxide nanobelts synthesized by chemical vapor deposition

Tungsten trioxide (WO₃) nanobelts in tetragonal structure were grown on Si substrates by a hot-wall chemical vapor deposition (CVD) method without using catalysts. The products were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM), Raman spectroscopy, and photoluminescence (PL) spectrum. The width of the nanobelts is in the range of 50–100 nm with width-to-thickness ratios of 5–10 and lengths of up to tens of micrometers. These nanobelts grew along the [0 0 1] direction and can be identified as the tetragonal WO₃ structures. Raman and PL measurements indicate the high quality of the nanobelts. The vapor–solid growth mechanism could be applicable in our experiment.     

Analytical model for chemical vapor deposition of SiO2 films using tetraethoxysilane and ozone

A theoretical model has been developed to analyze chemical vapor deposition (CVD) of SiO₂ from tetraethoxysilane (TEOS) and ozone. The model incorporates both homogeneous gas phase reactions and heterogeneous surface reactions. Two new kinetic mechanisms which include parasitic gas phase reactions are proposed to explain the observed decrease in deposition rate of SiO₂ films as the temperature is increased. The predicted values from the proposed model are found to agree well with all available experimental results over a wide range of experimental conditions. The effect of parasitic gas phase reactions becomes significantly more pronounced with increasing pressure and temperature. Correlations of experimental data on etch rate with surface concentrations predicted by the model at 60 Torr show that one can improve the film quality by increasing the ratio of O₃ to TEOS at the wafer surface, (O₃/TEOS)_wafer, and the wafer temperature.