Papers by Keyword: Chemical Vapor Deposition (CVD)

Abstract: A two-dimensional mathematical model for deposition behavior of SiC coating on C/C composites in a hot-wall CVD reactor was developed. Deposition rate of SiC was calculated by finite element method and optimized by using an orthogonal L9(3)4 test. The single and coupling effects of process parameters on deposition rate of SiC, including deposition temperature, the flux of mixed gases, the volume ratio of H2 and Ar, and that of MTS and mixed gases, were calculated and discussed. The optimal deposition rate of SiC was obtained.

Abstract: TiN films have been deposited on K211 super alloy substrates by chemical vapor deposition (CVD) using a gaseous mixture of TiCl4, NH3, and Ar as carrier gas between 400 and 700°C. The films were characterized by means of scanning electron microscopy and energy dispersive spectrometer. In this paper, the wear and corrosion resistance of TiN coatings have been investigated by abrasive experiments and corrosion tests. It was shown that coated samples demonstrated significantly higher wear resistance than those uncoated by weight loss measurements in the test procedure. Under the conditions of the corrosion experiments, substrates with TiN coatings showed better corrosion resistance than uncoated samples and stainless steel.

Abstract: One of the key problems in copper-diamond composites is the interface between the metal matrix and the diamond reinforcement. In order to take advantage of the high thermal conductive diamond filler in a composite the design of the interface is crucial. One approach to minimize the thermal contact resistance between metal and diamond reinforcement is to coat the diamonds with functional layers, e.g. Mo or W. For coating of diamonds PVD and CVD have been used followed by characterization of coating thickness by different methods. The coated diamonds were used for composite manufacturing and the thermal diffusivity of the compacted materials was measured.

Abstract: The physico-chemical fundamentals (thermodynamics, kinetics) of tungsten carbides crystallization process are presented. Chemically vapor deposited coatings composed of tungsten carbides, metallic tungsten matrix with nanoparticles of tungsten carbides are synthesized from gaseous mixture of tungsten hexafluoride, hydrogen and propane at temperatures ranging from 623 to 923 K and can be used as materials for extreme environments. The physical and mechanical characteristics of these CVD coatings are discussed.

Abstract: Several 2D SiCf-SiC and Cf-SiC composites were fabricated using isothermal and isobaric Chemical Vapour Infiltration (ICVI) process. The reinforcements used in the above composites are Nicalon CG fabric and C fabric. Prior to SiC matrix infiltration, BN and C interfaces were applied to the fibre by using the pre-cursors Boron Trichloride (BCl3)-Ammonia (NH3) and Methane (CH4) respectively to improve the mechanical performance of the composites. SiC matrix was infiltrated by the decomposition of Methyl Trichloro Silane-CH3SiCl3 (MTS) in the presence of hydrogen at the temperature ranging from 950°C to 980°C. H2/MTS flow rate ratio used for this study is 16:1.An appropriate temperature for uniform SiC infiltration without any premature pore closures have been obtained by kinetic experiment. Density and porosity of the above composites were measured using the method described by EN1389:2003. Various mechanical characterizations like flexural strength, tensile strength and fracture toughness of the SiCf-SiC composites were also studied. The SiCf-SiC composites were subjected to thermal exposure (1000°C for 100 hr in an oxidizing atmosphere) and tensile strength results obtained before and after thermal exposure were compared. RT Flexural Strength and Fracture Toughness (KIC) of composite-SQAV (SiCf/C/SiC) and composite-SQBII ( SiCf/BN/SiC ) are measured by 3-point bending and results were compared. RT Flexural strength of Cf-SiC composites with C interface of two thicknesses were measured and

Abstract: Cubic SiC/Si (111) template is an interesting alternative for growing GaN on silicon. As compared with silicon, this substrate allows reducing the stress in GaN films due to both lower lattice and thermal expansion coefficient mismatch, and can provide better heat dissipation. In this work, we first developed the epitaxial growth of 3C-SiC films on 50mm Si(111) substrates using chemical vapor deposition. AlGaN/GaN high electron mobility transistors were grown by molecular beam epitaxy on these films. Both the structural quality and the electrical behavior of these structures show the feasibility of this approach.

Abstract: The formation of dots by CVD in the hetero-system SiC-Si was studied in the two possible ways : Si dots on SiC substrate and SiC dots on Si substrate. The substrates underwent special surface treatment to reveal a network of parallel steps before deposition of the dots. In the Si on SiC case, the dots density on the 8°off 4H-SiC substrate varied in the range 107 – 7x108 cm-2 and mainly depends on the SiH4 flux and the deposition time. The Si dots are in majority aligned along the step edges of the substrate. In the other hetero-system, only propane was introduced in the reactor to performed a localised carbonisation of the Si(111) 1.5°off substrate. The SiC dots obtained at 1200°C have similar density the Si ones but with smaller size.

Abstract: To elucidate the origin of giant step bunching on 4˚ off-axis 4H-SiC (0001) faces, we carried out hydrogen etching and epitaxial growth under various conditions. We found that giant step bunching occurs during hydrogen etching and epitaxial growth at extremely low or high C/Si ratios, i.e., with an excessive supply of SiH4 or C3H8. From these results, we have proposed that the origins of giant step bunching are asymmetry in the step kinetics in etching and Si or C cluster generation on terraces during growth.

Abstract: We have developed a new chemical vapor deposition (CVD) system that is capable of a high growth rate of over 100 µm/h with good uniformities of thickness and carrier concentration. In this CVD system, the process gases contribute efficiently to epitaxial growth. In a demonstration of the abilities of the CVD system, we achieved an average growth rate of 140 µm/h, a thickness uniformity of 3.9%, and a carrier concentration uniformity of 8.9% in a 2-inch wafer, without degradation of the crystallinity.

Abstract: The structural and morphological modifications induced by the carbonization stage upon 3C-SiC heteroepitaxial films grown on (111) and (100) oriented silicon substrates have been investigated. The crystalline quality of the films is strongly dependent on the carbonization parameters (propane flow rate and duration of carbonization). The (111) heteroepitaxial films coalesce more rapidly and present a lower dependence on the carbonization conditions than (100) films. By comparing the evolution of the interfacial defects (voids) density with existing models, we show that this is related to the initial mechanisms occurring during the carbonization stage. The twin defects densities on (111), (100) and (211) films are also investigated and the role of the only carbonization stage on their formation is studied.