Kinetic and gas-phase study of the chemical vapor deposition of silicon carbide from C2H3SiCl3/H2

The chemical vapor deposition (CVD) of silicon carbide from vinyltrichlorosilane (VTS) was studied to identify a range of conditions leading to pure crystalline SiC. The deposition rate was recorded to evidence the various deposition regimes. Gas phase, elemental analyses and infiltration tests were also performed. Three distinct chemical reaction regimes were identified. In CVD conditions, carbon is co-deposited at low temperature while VTS is only partially decomposed. In infiltration conditions, the composition switches to pure SiC inside the porous substrate because of a depletion of reactive hydrocarbon species. Competing heterogeneous reactions are responsible for a hysteresis versus temperature, in both deposition rate and composition of the deposit. The high temperature domain is the most suitable to deposit pure crystalline SiC in CVD conditions. Hydrogen dilution strongly accelerates the homogeneous decomposition of VTS as compared to argon. Assumptions on the reaction mechanism were proposed describing the chemistry of this precursor

Synthesis and optimization of low-pressure chemical vapor deposition-silicon nitride coatings deposited from SiHCl3 and NH3

Stoichiometric silicon nitride films were deposited by low-pressure chemical vapor deposition from the SiHCl3-NH3-H2-Ar system in a hot wall reactor at pressures ranging from 0.3 to 2 kPa. The films are amorphous for deposition temperatures up to 1000 °C and crystalline, in the α-form, at 1200 °C and above. A method for evaluating the internal stresses based on the curvature of the silicon substrate wafer and the resulting silicon Raman peak shift was developed. Some amorphous films exhibit high internal tensile stresses that can lead to cracking during deposition depending on the mechanism and effective precursors involved. Residual stresses can thus be reduced and cracking avoided by, in descending order of importance, reducing the concentration of reactive gases through dilution, increasing the deposition temperature and decreasing the total pressure. The effects of these parameters on the intrinsic stresses were related to the amount of residual hydrogen successively incorporated and thermally released during the growth of the coating according to the Noskov's model

Chemical Vapor Deposition and Characterization of Thick Silicon Carbide Tubes for Nuclear Applications

International audienceSiC/SiC composites have an outstanding mechanical behavior under irradiation, but their high porosity excludes their use as nuclear fuel claddings in the future nuclear power plants. A complementary thick and tight SiC sheath could be a solution to ensure the first barrier towards fissile materials. The aim of this work is to make long, free standing and high strength SiC tubes. A few hundred micrometers thick tubular coatings were produced by chemical vapor deposition at atmospheric pressure, from CH3SiHCl2/Ar/H2 mixtures. Their chemical compositions and microstructures were studied by electron probe microanalysis, Raman spectroscopy and scanning electron microscopy. The deposition rate, composition and microstructure were investigated as a function of the substrate temperature and the gas flow rates. A Fourier transformed infrared spectroscopy analysis of the gas phase was carried out at the reactor outlet. The Si/C ratio, the SiC degree of crystallization and the surface morphology are strongly related to the maturation of the gas phase and the deposition regime

Structural and textural evolution of CVD-SiC to indentation, high temperature creep and irradiation

International audienceThe structure and microtexture of different SiC based CVD coatings have been studied by RMS, in their as-processed state and after high temperature annealing, creep, indentation and irradiation. Both annealing and creep resulted in the same degree of SiC crystal growth and decrease of stacking faults. A slight influence of stress was however observed on the structure and texture of the co-deposited free-carbon, supporting an intergranular creep mechanism. Room temperature indentation induces substantial structural disorders (dislocations, stacking faults, small grains) near the contact and more extended damages due to dislocation slip parallel to the compact Si-C planes. These structural changes were found to depend on the single crystal orientation and therefore, on the texture of polycrystalline SiC. Room temperature proton irradiation produced only small amounts of disorders. The specific alterations of the Raman features were explained using a phonon confinement model. They support very low scale defects, likely as punctual defects

Structure, microstructure and disorder in low temperature chemical vapor deposited SiC coatings

International audienceChemical vapor deposited SiC coatings were investigated at different scales by X-Ray diffraction, Raman microspectroscopy and transmission electron microscopy. They were prepared under specific conditions explaining the various (micro)structures obtained. The deposits all have a columnar morphology with a preferential orientation and a faulted cubic structure. They differ in how disorder is incorporated in the structure. Fine XRD analyses and stacking fault density assessment by TEM revealed the one-dimensionally-disordered (ODD) polytype in the textured coatings. The frequency and spatial distribution of stacking faults vary and sometimes locally generate periodic alpha sequences. A specific type of disorder was also identified where {111} planes are arranged parallel to the growth direction within the columns. These disorders, more energetic than stacking faults, induce multiple and particularly large Raman modes. Crystal distortions, such as dislocations, are localized at the ODD domain boundaries, which are frequently interrupted as they extend during the growth

Experimental study of the chemical vapor deposition from CH3SiHCl2/H2: Application to the synthesis of monolithic SiC tubes

International audienceThe aim of the present work is to synthesize high strength monolithic SiC tubes to improve the imperviousness of a SiC/SiC composite structure. A few hundred micrometers-thick tubular coatings were produced by chemical vapor deposition (CVD) at atmospheric pressure, from CH 3 SiHCl 2 /Ar/H 2 mixtures. The CVD-SiC tubes were obtained by deposition on the inner walls of a SiO 2-tube substrate, previously coated with a pyrocarbon interfacial layer to promote delamination. A continuous deposition process was developed to allow the realization of relatively long CVD-SiC tubes, by sliding the heating system along the substrate. The chemical composition and the microstructure of the tubes were studied by electron probe microanalysis, Raman spectroscopy and scanning electron microscopy. The deposition rate, composition and microstructure of the CVD-SiC coatings were investigated as a function of the substrate temperature and the gas flow rates. A Fourier transformed infrared (FTIR) spectroscopy analysis was carried out at the reactor outlet to characterize the gas phase reactions. The FTIR analysis of pure species from the Si-C-Cl-H system as well ab initio calculations at the density functional theory (DFT) level allowed the assignment of the main IR features in the experimental spectra and th

Methyldichloroborane Evidenced as an Intermediate in the Chemical Vapour Deposition Synthesis of Boron Carbide

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Methyldichloroborane Evidenced as an Intermediate in the Chemical Vapour Deposition Synthesis of Boron Carbide

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