Theoretical Study on the Reaction Mechanism of SiCl4 with H in the Gas Phase

25卷4期结构化学( JIEGOU HUAXUE)Vol 25. No 4f siCl with H in the Gas Phase anismTheoretical Study on the Reaction MechaSUN Ren-An LI Na" AI Chun-Zhi ZHANG Hong(Department of Chemistry, Liaoning Normal University, Dalian 116029, China)(Beijing No 161 High School, Beijing 100031, China)ABSTRACT The reaction mechanism of SiCla with H2 has been studied theoretically usingGaussian 98 program at B3LYP/6-311G* level. Three different reaction paths(a, b, c) in the gaphase were obtained. The geometries, vibrational frequencies and energies of every stagnation pointin the reaction channel were calculated and the mechanisms have been confirmed. the results showthat path a has an activation energy of 79. 12 kcal/mol, which was considered as the main reactionpath. Comparably, paths b and c have the energy barriers of 125.07 and 136. 25 kcal/mol,res-pectively. The reaction rate constant was calculated by TsT method over a wide temperature rangeof 900-1600 K, which further confirmed that path a was the main reaction channelKeywords: density functional theory, transition state, reaction mechanism, rate constant1 INTRODUCTIONr as theoreticalinvestigation, much attention was paid to build ma-Semiconductor silicon materials are vital for mi- thematic models about process according to the efcroelectronic and information industry. Silicon has fect of various parameters 7-l. But the reaction me-many advantages, for example, rich resource, out- chanism of SiCl4 with H2 has not been reported sostanding quality and sophisticated processing tech- far In present work, density function theory DFTnology. So it has been widely used in semiconduc- method was employed to investigate the microscopetor industry. One of the key techniques of mo- derreaction mechanism of SiCl4 with H2, which is premicroelectronic industry is epitaxial growth of single sent in epitaxial growth of single crystal siliconrystal thin film on single crystal silicon and its ba- Based on theory calculations, the main reactionchannel was determinedIn the chemical vapour deposition of Si, generallySiCl4 is used as silicon resource to produce silicon 2 CALCULATION METHODSepitaxial wafer. This technology has been extensively utilized in practical manufacture and life. CurAll the calculations were executed using gaussianrently, most of the experimental study upon this program 2. Geometrical configurations and enerreaction system was focused on the effect of tem- gies of reactants(R), products(P)and transitionperature, reactant condensation, current velocity and states(tS)in each reaction channel were optimizedother parameters on the epitaxial growth of silicon, with BERNY energy gradient method at dFt/or spectrum analysis on intermediates of reaction B3LYP/6-311G* level. Based on the obtained geoReceived 8 September 2005: accepted 20 October 2005O This work was supported by the Foundation of Education Committee of Liaoning Province(No中国煤化工2 Corresponding author. E-mail: sg422110(@mail. dlptt InCNMHGSUN R.A. et al. Theoretical Study on the reaction mechanism492of SiCl4 with H in the Gas Phasemetrical configurations of R, P and TS, single-point given for transition states(TS)nergy calculation and zero-point energy adjustmentAs shown in Fig. 1, in reaction channel a, H(1)were carried out with QCISD(T) method at 6- and H() atoms of H2 attack Cl(4) and Si(3)of Sicl4311G* level. The transition state was determined molecule, respectively, providing a transition stateupon the analysis from the unique imaginary vibra- of TSa. And then bonds Cl(4)-Si(3)and H(1-H(2)tion mode to reactant and product and further lengthen gradually till break at last, at the mean timeconfirmed with intrinsic reaction coordinate (irc) bonds H(1)-CI(4) and H(2-Si(3)shorten graduallyAt last. the reaction rateto produce SiHCl3 and HClevery reaction chI were computed using traIn reaction channel b, H(7) atom of H2 attackditional transition state theory (tst) in the temCl(2)atom of SiCla molecule to generate transitionperature range of 1000-1600Kstate TSb. Afterwards, bond Cl(2)-Si(I) breaks andCl(2)bonds with H(7). At thH(6)-H(7)3 RESULTS AND DISCUSSIONbond breaks to give products of SiCl3, HCI ant Hatom3. 1 Analysis of reaction mechanismAs far as reaction channel c, H(6)and H(7)atomsWhen hydrogen atoms of H2 attack different of H2 attack Cl(4)and Cl(3)of Sicl4 molecule,atoms of SiCl4 molecule, three possible reaction respectively, forming a transition state TSc. Afterhannels might exist, as shown in Fig. 1. The geo- wards, Cl(3)Si() and Cl(4)-Si(1) bonds break grametric configurations, main structural parameters dually, at the mean time, Ci(3)-H(6) and Cl(4-H(7and simple harmonic vibration frequencies of re- bonds strengthen and ultimately form chemicactants(R), products(P)and transition states(TS)in bonds, generating products of SiCl2 and two HCeach reaction channel are listed in Fig. I and Table 1. moleculesParticularly, imaginary vibration modes are alsoSil Clc16Fig 1. Bond lengths(nm)and bond angles( degree)of R Sand pandimaginary vibrational modes of transition st中国煤化工CNMHG2006Vol.25结构化学( JIEGOU HUAXUE) Chinese.Srct.Chem493Table 1. Predicted Vibrational Frequencies(cm)at the b3LYP/6-311G* Level5054210614612255TS2534122l110.395201221SiHCl38152861SiCIs4493,03For TSs of three reaction channels, intrinsic reac- show that in each elementary reaction, the abruptiontion coordinate(IRC) calculation was carried out of old bonds and formation of new bonds occurupon computation from the unique imaginary vibra- synchronously, indicating that the transition statestion mode of ts to reactant and product at we searched all are relative with corresponding re-DFT/B3LYP/6-311G*level. Fig. 2 shows changes of actants and products, and ultimately, verifying fur-energy and main bond lengths along with reaction ther the correctness of transition statescoordinate in three reaction channels. The resultsR[H(3)Cl(4213168H(2)SRIH(I)-CI(RIHOIHH0-15-100500051.01.5200510sl(amu). bos[(amu)bohrPath a: SiCl4+ H2-SiHCI3 HCIRISi(1)CIO彐2131.6218RH(6)Hx""…、RC(2.RICI2)-H(005st(aru)]中国煤化工Path b: SiCl4+H2-SiCl3+ HCl+ HCNMHGSUN R.A. et al. Theoretical Study on the reaction mechanism494of SiCl4 with H in the Gas PhaseSi(1-CI(213133213139R[Si(1)CI(213160RICI3H-HOP213161R[CI(4)-H(213161210-15100500Path c: SiCl4+ H2SiCl2+ 2HCIig. 2. IRC about all transition states3.2 Energy changes along reaction routesTable 2. Predicted Total Energies E(Hatree), ZPE(kcal/mol)and Reactive Energies(kcal/molat the Qcisd(t)/6-311G*and b3LYP/6-311G" LevelsB3LYP/6-311GOCISD(T)/6-311G*ZPER(SiCL+H2)-2131.78122129.0066-2131.6759128.8832Pa(SiHCl3+HCD2131760221289772128.8054Pb(SiCl3+HCI+H)-2131.6143-2128.8386101.83-2131-2128.7888136.2Pc(SiCl2+2HCI)9832131.680421288918SiCl3+HCl+E13625TS10183SiC1+2HCISicl4+HSiHCI+HCFig 3. Energy relationship of reactants, transition states and productsThe total energies (E), zero-point energies(ZPE), tion states and products at DFT/B3LYP/6-311Genergies(E") modified by QCISD(T)and relative level are listed中国煤化工energies of reaction system(AE)of reactants, transi-The resultsCNMHGenergy of2006Vol.25结构化学( JIEGOU HUAXUE) Chinese.Srct.Chemreaction channel a is 79.12 kcal/mol, suggesting that nel were computed using traditional transition statea is the main reaction channel. Comparably, chan- theory (TSt)in the temperature range of 1000nels b(125.07 kcal/mol)and c(136.25 kcal/mol) 1600 K. The results are given in Table 3possessing higher energetic barrier are secondaryAs revealed in Table 3. reaction rate constant inreaction channels. The results also reveal that all creases obviously with the heightening of temperareactions are endothermal, indicating the reactions ture. At higher temperature, the changing gradient ofmust be carried out at high temperature. The energy reaction rate is small and the reaction tends to be anrelationship of reactants, transition states and pro- equilibrium. Among the rate constants at the sameducts is given in Fig 3temperature, constant of channel a is the largest,3. 3 Reaction rate constantwhich further proves that a is the main reactionThe reaction rate constants of every reaction chanchannelTable 3. Rate Constants of the Reaction Path in the Range of 900-1600 K(cm - mor- s)4.6×1046×10-153.5×10466×10228×10-137.7×1026.9×10-15,1×103.8×101.0×10-73.2×1025,2×103.7×102.121027×1025.0×10160043×1034.0×1028×1034 CONCLUSIONsibility of occurrence of these two reactions. TheThree possible reaction channels(a, b, c)of SiCl, were computed using traditional transition statH2 system in gas phase were investigated. The re- theory (Tst) in the temperature range of 1000-sults show that a is the main reaction channel with 1600 K. We found that at the same temperatureenergetic barrier of 79. 12 kcal/mol. Comparably, b constant of channel a is the largest, which furtherand c have the energetic barriers of 125.07 and proves that a is the main reaction channel136.25 kcal/mol, respectively, suggesting a low posREFERENCES(1) Nishizawa, J, Terasaki, T; Shimbo, M. J. Crystal Growth 1972, 17, 241-248(2) Sedgwick, T O; Smith, J E J. Crystal Growth 1975. 31, 264-273(3) Ohshita. Y: Hosoi, N.J. Crystal Growth 1993, 131, 495-500(4) Brown, A R. Doren, D. J.J. Chem. Phys. 1999, 110, 2643-2651(5) Wong, T C; Yu, CC. Wu, JJJ Crystal Growth 2002, 243, 419-426(6) Wong, T C; Wu, JJJ. Thin Solide Films 2003, 47, 45-50中国煤化工(7) Shepherd, W.H. J Electrochem. Soc. 1965, 112, 988-99CNMHGSUN R.A. et al. Theoretical Study on the reaction mechanismofSiCl4 with H in the Gas Phase3) Van der putte, P. L; Giling, J. Bloem, J.J. Crystal Growt 1975, 31, 299-3079) Korec, J.J. Crystal Growth 1979, 46, 362-370(10) Bloem, J. Claassen, w. A. P: Valkenburg, W G, J N., Journal of Crystal Growth 1982, 57, 177-184(ID) Gupta, P. 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