Mechanisms for NH3 Decomposition on the Si(111)-7 × 7 Surface: A DFT Cluster Model Study

Abstract

Density functional theory at the level of (U)B3LYP has been employed to explore the complete dissociation of NH 3 on the Si(111)-7 x 7 surface. The results were compared and contrasted to those of the Si(100)-2 x 1 surface. Our calculations demonstrated that there existed competing factors, which determined the selectivity of various surface sites on every step of N-H bond dissociation. The initial N-H bond dissociation from NH 3 to form the adsorbed NH 2 species was most preferential on the rest atom site (Si r ) of Si(111)-7 x 7. This was attributed to a high probability of trapping the incident ammonia on the Si r site. Further N-H bond dissociation can be facilitated by the elevated temperature, which started by an NHx (x = 2 and 1) insertion, followed by an H-transfer process. Although the NH 2 insertion into the Si-Si backbond on the Si(100)-2 x 1 surface was found to be the easiest, the NH insertion was most feasible on the adatom site (Si a ) of Si(111)-7 x 7. These results can be used as the quantum mechanical input for chemical kinetics model of chemical vapor deposition and should be of significance in the microelectronic industry.