Theoretical Studies On The Reaction Mechanism Of BCl₃ With H₂ In Epitaxy Growth Of P-type Silicon

In this paper, the mechanisms of the reaction which take BCl₃/H₂ as impurity source gases were investigated theoretically for the first time. The geometries of all reactants, transition states, intermediates and productions have been optimized at the BHandHLYP/6-311G** level. The active energy of each reaction channel was calculated. Analysis the imaginary vibration mode of all transition states and IRC (intrinsic reaction coordinate)in order to confirm the transition states.The paths of the reaction in the gas phase was calculated, the results show that BCl₃ react with H₂ can get BHCl₂ and HCl. BHCl₂ can continue to react with H₂ and get BH₂Cl and HCl. BHCl₂ also react with H₂ and get the final product: BH3 and HCl. We investigated the whole reactions that occurs in the gas phase, and found that there is no boron atom appeared. The active energy of the reaction between BCl₃ and H₂ is the highest in the gas phase. So it is the determinable rate step of reactions.The Si₂, Si₃ and Si₄ clusters were chosen for simulating the silicon substrate. The mechanism of the reaction on the substrate surface was calculated, and it is found that the crystal that was not been formed in the gas phase can formed on the silicon substrate surface. The active energy of the reaction between the adsorptive production and H₂ or H atom is lower than that in the gas phase. The active energy of decomposition is the highest on the substrate, but it has decreased a lot compared with striping down HCl straightly in the gas phase. So we can conclude that the active energy is reduced much by the silicon substrate joining in the reactions.In this paper, we gave some explanation for the experiment of the p-type silicon vapor-phase epitaxial growth and the microcosmic mechanism of the reactions theoretically. It will provide the dynamical information for the experimental workers to design the experimental techniques and improve the work efficiency.