Impinging Jet Reactor Research Articles

Chemical Vapor Deposition of Silicon from Disilane under Reduced Pressure in a Circular Impinging Jet Reactor: Simulation and Experiments

The chemical vapor deposition of silicon from disilane under reduced pressure in an impinging jet reactor has been studied experimentally and simulated numerically by a 2D model. The measured deposition rate and profile have been compared to the results of the calculations performed with various hypotheses concerning both gas‐phase and surface reactions. The influence of the number of species considered, of the kinetic rate constants, and of the models used for the reactive sticking coefficient of silane and disilane were investigated. Among the 17 species that may be present in the gas phase, a mechanism including 8 silicon‐carrier species has been determined to represent satisfactorily the deposition rate and profile experimentally observed.

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

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.

Numerical Analysis of an Impinging Jet Reactor for the CVD and Gas-Phase Nucleation of Titania

AbstractWe model a cold-wall atmospheric pressure impinging jet reactor to study the CVD and gas-phase nucleation of TiO2 from a titanium tetra-iso-propoxide (TTIP)/oxygen dilute source gas mixture in nitrogen. The mathematical model uses the computational code FIDAP and complements our recent asymptotic theory for high activation energy gas-phase reactions in thin chemically reacting sublayers. The numerical predictions highlight deviations from ideality in various regions inside the experimental reactor. Model predictions of deposition rates and the onset of gas-phase nucleation compare favorably with experiments. Although variable property effects on deposition rates are not significant (∼11% at 1000K), the reduction of rates due to Soret transport is substantial (∼75% at 1000K).

On the rate and uniformity of CdTe deposition in an impinging jet reactor: experimental results

Cadmium telluride was deposited by the pyrolysis of organometallic precursors in an impinging jet reactor. The deposition was nonuniform when mass transfer limitations were significant. The deposition rate decreased when hydrogen pressure was decreased from 720 to 100 Torr; experiments with inert gases demonstrated the dependence of the reaction rate on the presence of hydrogen. Minima appeared in the deposit profile at low nozzle heights and high flow velocities. Enhanced sublimation of CdTe and slight cooling of the substrate might be responsible for this phenomenon.

On the rate and uniformity of CdTe deposition in an impinging jet reactor: numerical simulations

The impinging jet with a parabolic inlet profile was modeled numerically and the results were compared to an existing series solution. The results at nozzle heights of 0.5 radii and above agreed within 1% of the series solution, but discrepancies of several percent were obtained at nozzle heights below 0.375 radii where the series solution did not converge well. Numerical solutions that allowed for thermal gradients, details of an actual impinging jet reactor, and cadmium telluride deposition from organometallic precursors, were also obtained. The experimentally-derived mass-transfer-limited deposition profile and the model simulations agreed when the model's concentrations at the bubbler outlets were reduced by a factor of four from the saturation values. This correction was justified when an inventory of reactant revealed that the mixtures at the bubbler outlets were far from saturated.

Catalytic etching of Pt/Rh gauzes

The catalytic etching of 90% (weight) platinum/10% rhodium gauzes in hydrogen/oxygen mixtures was studied. The gauzes were found to etch over exactly the same range of temperatures and gas stoichiometries as pure platinum. In contrast, pure rhodium etched in neither pure gases nor under reaction conditions. In a laminar flow type reactor weight loss of the Pt/Rh gauzes was found to be significant indicating rapid etching and the surfaces smooth and undifferentiated from the untreated material. In contrast, in an impinging jet reactor there was little weight loss, but the surfaces were found to be partially covered by complex particle structures, 1 to 10 μm across. Analysis of the particles showed them to have virtually the same composition as the original gauze. The application of a new model of catalytic etching of single metals to this system explained some, but not all, of the observations. The model explains the limited range of conditions under which etching was observed, as well as the formation of particles in the impinging jet reactor; however, the model failed to explain completely the presence of rhodium in the particles.

The Wet Etching of CdZnTe Substrates for OMVPE Growth

ABSTRACTThe etching of CdZnTe substrates by bromine-methanol solutions was studied by chemi-mechanical polishing. Over a bromine concentration of 0.5 to 3.5 volume percent, the etch rates varied linearly with bromine concentration, were independent of substrate orientation, and, within experimental uncertainties, were identical to those for the etching of CdTe. The etched samples were used as substrates for the organometallic vapor phase epitaxy (OMVPE) growth of CdTe in an impinging jet reactor. The bromine concentration used in etching did not affect the growth rate or the morphology of the deposited CdTe films, but a higher defect density was found for the film grown on a substrate with the orange-peel structure.

Simultaneous Chemical Vapor Deposition of Boron Nitride and Aluminum Nitride

Two chemically different phases, hexagonal BN and AIN, were simultaneously produced by chemical vapor deposition (CVD) using an impinging jet reactor and the BCl3─AlCl3─NH3─Ar reagent system. The microstructure of the BN + AIN composite coatings was strongly dependent on temperature, pressure, and BCl3 and AlCl3 concentrations. The growth characteristics of BN and AIN in the codeposition system were similar to those expected from the single‐phase deposition processes (i.e., BN‐CVD and AIN‐CVD), except the growth of AIN whiskers was accentuated, and competition between BN and AIN deposition in the composites was suspected to be the cause of less‐crystalline deposits. In both BN + AIN‐CVD and AIN‐CVD, the growth of AIN whiskers became more apparent with increasing pressure or temperature. The codeposition behavior observed experimentally was compared with thermodynamic predictions.

Kinetic Analysis of Chemical Vapor Deposition of Boron Nitride

BN was deposited on Al2O3 substrates from the BCl3─NH3─Ar reagent system. An impinging jet reactor configuration was used to obtain kinetic data in the temperature range of 800° to 1000°C and in the pressure range of 4 to 20 kPa. The BN deposition could be described by a simple kinetic rate expression with an activation energy of about 39 kcal/mol and a first‐order dependency on BCl3 concentration. The BN deposition rate increased with temperature, pressure, and BCl3 concentration. The microstructure of the BN coatings was not strongly influenced by the process parameters.

Kinetic and Thermodynamic Analyses of Chemical Vapor Deposition of Aluminum Nitride

AIN coatings were prepared by chemical vapor deposition from the AlCl3—NH3—Ar reagent system using an impinging jet reactor in the temperature range of 700° to 1100°C. A mass transfer model and thermodynamic calculations were used to analyze the deposition data. The AIN‐CVD process could be approximated by calculating mass transfer—thermodynamic limits at low AlCl3 concentrations. The AIN deposition rate decreased drastically with increasing temperature above 1000°C in agreement with thermodynamic predictions. At high AlCl3 concentrations, a surface kinetic mechanism involving AlCl3 adsorbed on the deposition surface appeared to be the rate‐limiting step. The AIN deposition rate decreased on increasing the AlCl3 concentration or total pressure. The crystalline structure of AIN was strongly influenced by the processing parameters. The AIN coatings became highly crystalline and preferentially oriented with an increase in the AlCl3 concentration or pressure.

Growth of CdTe by organometallic vapor phase epitaxy in an impinging jet reactor

Deposition of (100)CdTe epilayers by organometallic vapor phase epitaxy (OMVPE) has been investigated using a vertical downward flowing impinging jet reactor with dimethylcadmium (DMCd) and diethyltelluride (DETe) as the organometallic sources. An Arrhenius plot of deposition rate versus substrate temperature had a linear region over a wide temperature range from 320 to 480 °C, corresponding to an activation energy for growth of 18 kcal/mol. Surfaces of (100)CdTe epilayers had high densities of pyramidal hillocks. Double-crystal x-ray rocking curves, however, were not affected by the presence of the hillocks. Full widths at half maximum for the (400) reflection of less than 30 arcsec were obtained for growth temperatures from 400 to 480 °C. At 460 °C rocking curves for the epilayer were nearly identical to the substrate demonstrating that films whose quality matches that of the underlying substrate can be deposited in the impinging jet system.

Theoretical Analysis of Chemical Vapor Deposition of Ceramics in an Impinging Jet Reactor

A mathematical model for chemical vapor deposition in an impinging jet reactor is extended to consider growth of materials that are nonstoichiometric or that contain multiple solid phases. The model treats the fluid flow of the reactant gas mixture, multicomponent heat and mass transfer, and simultaneous gas‐phase and surface reactions. For a given system, insight into the rate‐limiting steps can be obtained by identifying a set of reaction rate constants that gives a match between theoretical results and experimental data. The calculations also provide quantitative information on the relationships between operating conditions, deposition rate, and deposit composition. Results for production of boron carbide from BCI 3, CH4, and H2 are presented as an example. Under typical processing conditions, deposition of By C is found to be controlled primarily by the rate of CH4 decomposition and the extent of surface coverage by CH4 Theoretical calculations are presented for different sets of operating conditions to illustrate the predictive capability of the model. Also, the sensitivity of results to various reaction mechanisms and to values for solid‐phase activities is evaluated. Analogies are drawn between the boron carbide process and deposition of other ceramics in which a carbon‐containing reactant is used.

The Sensitivity of CVD Calculations to Physical Property Values

A mathematical model that describes chemical vapor deposition in an impinging jet reactor has been used to assess the sensitivity of theoretical predictions to physical property values for intermediate species. Uncertainties in thermochemical data for a species have greatest impact on predicted deposition rates when the composition level of that species near the surface is comparable to the local compositions of the reactants. Under these circumstances, relatively small changes in the values of thermodynamic quantities used for the species can produce significant differences in deposition rates calculated under equilibrium conditions. Also, with the modified property values, different values of the kinetic parameters may be required to fit available experimental data, and this can lead to different interpretations of the rate‐limiting steps in the process. Quantitative information for chemical vapor deposition of boron from boron trichloride and hydrogen is presented.