REACTION THERMODYNAMICS IN CHEMICAL VAPOR DEPOSITION OF BORON CARBIDES WITH BCl₃–C₃H₆ (PROPENE)-H₂ PRECURSORS

Abstract

The gas phase reaction thermodynamics in the chemical vapor deposition (CVD) process of preparing boron carbides via the precursors of BCl 3– C 3 H 6(propene)– H 2 is investigated with a set of 325 gaseous species, in which the data for 135 species are evaluated in this work. The thermochemistry data are calculated with accurate model chemistry at G3(MP2) and G3//B3LYP levels. The concentration distribution of all of the 325 species is obtained with the principle of chemical equilibrium. The thermochemistry data include the heat capacities, entropies, enthalpies of formation, and Gibbs free energies of formation. The heat capacities and entropies at temperatures in 298.15–2000 K are evaluated with the standard statistical thermodynamics. The Gibbs free energies of formation in 298.15–2000 K are calculated with the classical thermodynamics based on the developed heat capacities and entropies. By including the crystal B 4 C , C (graphite), and B , the results for an example of the 3:1:2 precursors of BCl 3: C 3 H 6: H 2 show that the crystal B 4 C can be produced at temperatures higher than 700 K while the graphite has a higher molar value and can be produced at lower temperatures. It is also examined that the production of graphite can be controlled by changing the ratio of the injected reactants or pressure. It is interesting that BHCl 2, BCH 3 Cl 2, BH 2 Cl , and B 2 Cl 4 are found to be the most effective species in the CVD process, which is similar to those in the BCl 3– CH 4– H 2 system. The results predicted in this work are consistent with the experiments.

Thermodynamics of the Production of Condensed Phases in the CVD of Methyltrichlorosilane Pyrolysis

“…The temperature region is chosen for two reasons. One is that the temperature generally adopted for CVD lie inside the region, and the other is that the new database [75][76][77][78][79][80][81] is for 298.15-2000 K. The pressures are chosen since 0.6 and 100 kPa are the lower [55] and upper [45] limits of the experimental and theoretical pressures found in the literature, [11, and 6 kPa is the typical experimental pressure used in our group. [83] 10:1 is also the most frequently adopted H 2 /MTS ratio either in experiments [11,31,35,36,38,39,45,46,51,[57][58][59][60] or in theoretical investigations.…”

“…As the main features of the co-deposition of the solid phases as a function of the experimental parameters of the process are already known, [11,[20][21][22][23][24][25][26][27][28][29]43,[57][58][59][60][61][62][63][64][65][66][67][68][69][70][71] an optimization and application of a new database is another main motivation for our work. For these reasons, we carried out thermodynamic data evaluations in the H 2 /MTS system [75][76][77][78][79][80][81] with accurate model chemistry methods. The results show that all of the theoretical data are consistent with the reliable experimental results.…”

“…6. Comparison of the composition of condensed phase obtained in this work and from the FactSage code [84] with its embedded database [85] at H 2 / MTS ratios in the range 10 therefore this work, by employing an assessed, more reliable, and more complete database [75][76][77][78][79][80][81] than is usual, is interesting, although the difference between the two data sources is not significant, as shown in Figures 2,4, and 6.…”

NEW REACTION PATHWAYS OFPROPENE + BCl3DECOMPOSITION IN CHEMICAL VAPOR DEPOSITION PROCESS

“…For the carbon rich system (propene þ BCl 3 ) in the gas phase reactions, the experiments have determined the preparation conditions 11,12 as well as the apparent activation energy of 208.7 kJ/mol. 13 In understanding the insights of the reactions, a theoretical study of the thermodynamics 14 and part of the reaction paths 19 were carried out in our group. However, the work is far from satisfactory.…”

Decomposition reaction rate of BCl3–CH4–H2 in the gas phase

“…For example, in a simple reaction system of BCl 3 -CH 4 -H 2 precursors, only two intermediates (IMs) HBCl 2 and HCl were observed with in situ FTIR [10], whereas 150 molecular species (including radicals) were found theoretically. Also in the theoretical study of reaction thermodynamics, 325 possible gaseous species were identified in the homologous reaction system of BCl 3 -C 3 H 6 (propene)-H 2 precursors [17]. In the study of the reaction paths and kinetics of BCl 3 -propene-H 2 system, 182 intermediates and 176 transition states (TSs) were found [18][19][20] with the first principles.…”