Atomistic modeling of chemical vapor deposition: silicon nitride CVD from dichlorosilane and ammonia

The mechanism and kinetics of chemical vapor deposition of silicon nitride films from SiH2Cl2 and NH3 have been studied theoretically by ab initio (MP2/MC-31G(d,p) and MP2/6-31G(d)) methods combined with the transition state and RRKM theories. Reactions involving the starting reagents and no more than one of the initial reaction products are included in the analysis. It has been found that, in the gas phase at least at T<1000 K, the formation of SiH(NH2)Cl through a bimolecular reaction between SiH2Cl2 and NH3 dominates over the dissociation of SiH2Cl2 to silylenes followed by silylene insertion into NH bonds. The mechanism of Si3N4 film growth has been examined using cluster models of the silicon nitride surface and surface groups chemisorbed on this surface. It has been found that the dangling bonds on the pure (0001) surface are relaxed to form diatomic >SiN surface groups. The calculated SiN bond length 1.62 A is considerably shorter than typical lengths of crystalline SiN bonds (1.74–1.76 A), and the surface atoms of these diatomic groups are significantly displaced from their bulk crystalline positions.