F. Teyssandier

Theoretical approach to chemical vapour deposition in the atomic system Ti-Si-C-CI-H

Etude du diagramme de phase du systeme Ti-Si-C et estimation des energies libres de formation des composes solides de ce systeme

Thermodynamics and Kinetics of Gas‐Phase Reactions in the Ti‐Cl‐H System

A mechanism and associated rate constants for the gas-phase chemical reactions that occur during the chemical vapor deposition (CVD) of titanium from titanium tetrachloride (TiCl{sub 4})/hydrogen mixtures is presented. TiCl{sub 4} is the most widely used inorganic precursor employed in the CVD of titanium-containing materials, such as titanium nitride, titanium carbide, and titanium diboride. In this work, rate constants for the unimolecular decomposition reactions of the titanium chlorides were predicted using Rice-Ramsberger-Kassel-Marcus theory for unimolecular reaction, while the rate constants for bimolecular reactions between TiCl{sub n} species and hydrogen atoms were estimated using an empirical correlation. Calculations at thermodynamic equilibrium over a range of temperatures and total pressures characteristic of Ti CVD conditions are presented first. The time-dependent evolution of the gas-phase composition is then simulated using the proposed mechanism. The results suggest that equilibrium predictions of gas-phase concentrations should be a good approximation at 1,500 K, unless very short residence times and low pressures are involved. In contrast, equilibrium calculations do not accurately reflect the gas-phase composition at 1,000 K.

2D modelling of a non-confined circular impinging jet reactor; Si chemical vapour deposition

The 2D modelling of a chemical vapour deposition reactor with a non-confined impinging jet configuration has been undertaken. The deposition rate of silicon from an initial gas mixture composed of SiH4-H2 has been numerically investigated as a function of various parameters such as substrate temperature, total pressure, gas flow rate, distance between nozzle exit and substrate, and direction of the jet with respect to the gravity field to determine the role of natural convection. Both gas-phase and surface reactions were considered in the 2D model which takes into account variable physical properties. It is concluded that intermediate species generate specific thickness profiles. In addition, the kinetic control case is compared to the upper limit case of deposition rate where the gas phase is supposed to be in chemical equilibrium.

Rate constants of reactions involving SiH4 as an association product from quantum Rice–Ramsperger–Kassel calculations

Quantum Rice Ramsperger Kassel (QRRK) calculations are carried out to calculate the pressure-dependent rate constants of reactions involving SiH4 as an association product. It is shown that good estimates of pressure-dependent rate constants can be obtained from QRRK in spite of the very poor treatment of the activated complex in this simple theory. However, possible errors arising from energy truncation must be avoided and reliable kinetic data must be fitted in order to select the final value of the adducts mean vibrational frequency. The results obtained in this work are satisfactorily compared with the experimental data available and with previous RRKM calculations. Parameterized forms of the pressure-dependent rate constants are derived for several bath gases, which can be used over the whole pressure and temperature range of interest for chemical vapour deposition (CVD) and related processes.

SiCTiC multiphased materials obtained by CVD

Abstract Carbide composite structures have been prepared by thermal chemical vapour deposition under atmospheric pressure from an input gaseous mixture composed of SiH2Cl2C4H10TiCl4H2. Their morphologies are strongly dependent on the composition of the input gases leading to either micro- or nanostructures. The latter were investigated by transmission electron microscopy. High resolution observations have revealed the microstructural arrangement of phases. On the basis of these characterizations, a spatial arrangement of the components which fits the composition variations in the deposits is proposed.

tert-Butyl-substituted vanadocene, (C5H4CMe3)2V: a precursor for MOCVD of pure vanadium carbide

tert-Butyl-substituted vanadocene, (C5H4CMe3)2V (1), is used as a precursor in the CVD preparation (740 °C under hydrogen at atmospheric pressure on steel substrates) of crystalline VC0.88 thin films, characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and electron probe microanalysis with wavelength dispersive spectroscopy (EPMA–WDS), which are not contaminated by graphitic carbon or oxygen. 1 was obtained by reaction of (C5H4CMe3)Na with [(V2Cl3)(THF)6]2(Zn2Cl6) and characterized by X-ray crystal structure analysis [monoclinic, P21/n; a= 6.164(1), b= 11.263(2), c= 11.842(2)A, β= 96.31(2)°; V= 817.2(7)A3; Z= 2]. A possible mechanism for the deposition of VC films from 1 is proposed.

Two-dimensional modelling of a non-confined circular impinging jet reactor—fluid dynamics and heat transfer

Abstract Coupled momentum and heat transfers have been numerically studied in a non-confined, axisymmetrical, laminar, and initially cold jet impinging on a flat substrate heated at high temperature. Variable physical properties were taken into account. The flow field as well as the local heat transfer rate was studied as a function of various parameters such as Reynolds and Froude numbers, nozzle-substrate distance, substrate temperature, and jet directions (upwards, downwards). The calculated flow field as well as the local Nusselt number are in good accordance with the experimental data from the literature at low temperature difference between the gas and the substrate. The numerical solution describes satisfactorily the non-monotonous experimental radial variation of the Nusselt number at small nozzle substrate distance.

The Influence of Carbon Precursors on the Gas-Phase Chemistry of Titanium Carbide CVD

The influence of carbon precursors, such as methane (CH 4 ), acetylene (C 2 H 2 ), and propane (C 3 H 8 ), on the gas-phase chemistry of the Ti-C-Cl-H system used to deposit titanium carbide (TiC) from titanium tetrachloride (TiCl 4 ) was investigated by calculating the thermodynamic equilibrium and modeling rate equations from a proposed kinetic model. Differences in the resultant gas-phase chemistries for reactions under reduced pressure at 1500 K are discussed. Initial mixtures of TiCl 4 , H 2 , and a hydrocarbon that produced identical equilibrium compositions were determined. Results for the Ti-C-Cl-H system for all three hydrocarbon precursors are compared to those of Ti-Cl-H and C-H in order to further illustrate the differences in thermal stability of key constituents, as well as the extent of conversion. Regardless of which carbon precursor is present, species belonging to the Ti-Cl-H subsystem are near equilibrium within 5 s. Conversely, species emanating from CH 4 decomposition in the Ti-C-Cl-H system are predicted to be far from equilibrium and unreactive with TiCl 4 . In contrast, the preponderant species under thermodynamic equilibrium, C 2 H 2 , provides a uniform source of carbon at any residence time. Finally, the stability of C 3 H 8 in the Ti-C-Cl-H system is significantly greater than in the C-H system. This greater stability is accompanied by a significant variation in the rate of by-product formation, suggesting that TiCl 4 and its subchlorides effectively compete with C 3 H 8 for important reactive intermediates. In the case of C 3 H 8 , a reaction flow analysis was carried out identifying the three main reaction paths that are responsible for propane decomposition, the further links that appear between these paths, and how the paths vary over time.

Optimization of a wall-less like reactor by simulation

Abstract A wall-less-type reactor is modelled in order to design a convenient device for the investigation of gas-phase reactions. With a reactor fitted with two concentric tubes, different flow configurations are analysed based on the flow pattern, and the chemistry both in the gas phase and on the surface. Optimal design has been determined using the well-known silicon chemical system as test case, taking into account eight reactive species and seven gas-phase reactions. Partial validation of the model is obtained by comparison of the calculated flow field with laser sheet visualization experiments.

Gas-phase kinetics analysis and reduction of large reaction mechanisms exemplified in the case of SiC deposition

Abstract Chemical vapor deposition (CVD) is commonly used to grow epitaxial SiC layers at relatively high temperature from SiH 4 –C 3 H 8 –H 2 mixtures. In order to model the deposition process, the kinetics of the gas-phase reactions involved must be known accurately and the main reaction pathways must be identified. For this purpose, we have selected the most recent sets of reactions and related kinetic data available for the C–H and Si–H chemical systems. However, the full mechanism so obtained is too large to be included in a CVD reactor model, because of the computational time required for the calculations and numerical convergence problems. As a consequence, the full mechanism has been reduced using the so-called ‘redundant species and reactions’ method due to Turanyi. Since reactions between Si–H species and C–H species have not been considered, the C–H and Si–H mechanisms have been reduced separately. As a result, a smaller subset of reactions and species describing accurately the gas-phase reactivity in the Si–C–H system has been obtained.