Theoretical Studies On The Reaction Mechanism Of PCl₃ With H₂ In Epitaxy Growth Of N-type Silicon

In this paper, the mechanisms of the reaction about N-type doping polysilicon which take PCl₃/H₂ as phosphor source were investigated theoretically for the first time with Gaussian98 program at B3LYP/6-311G** level. The geometries of all reactants, transition states and productions have been optimized. The active energy of each reaction channel was calculated. Analysis the imaginary vibration mode of all transition states in order to test the transition states. IRC (intrinsic reaction coordinate) was made for confirming the existence of the transition states, further.The reaction of PCl₃/H₂ in gas chromatography is multi-steps and multi-paths. at the beginning of gas chromatography reaction, there are four potential paths, PCl₂H and HCl are the primary reaction products. at the PHCl₂ will further react with H₂, there are five potential paths, PClH₂, PCl, and HCl are the primary reaction products. at the PClH₂,PCl will further react with H₂, there are six potential paths, PH3,PH and PCl are the primary reaction products. There are three of reactions among the PH3, PH and PCl products, phosphorus is attained in the PH + PCl reaction. The major reaction path is a1-a2-a3 while a1-e2-e3 competes fiercely, and phosphorus is obtained in the PH + PCl reaction through a6 and b6 paths. The Si₂, Si₃ and Si₄ clusters were chosen for simulating the silicon substrate, PCl₃ First Occur dissociative adsorption on Silicon, activation energy has less, reaction is easy to occur. Then the absorption offspring with H₂ pass the reaction of four-steps and multi-paths, finally one Cl atom of the absorption offspring and one H atom of the H₂ combined to HCl, and the other H atom of the H₂ separately precipitates, so crystal growing accomplished. The active energy of the reaction between the adsorption of PCl₃ on silicon and H₂ is lower than that of PCl₃ direct react with H₂ in gas phase. So we conclude that the silicon substrate has the catalysis in the reaction process.So, the doping crystal is attained by the phosphorus cluster depositing to the silicon substract surface , the phosphorus cluster is got pramilay via PCl₃ reacting with H₂ in the vapor phase.