AVS 46th International Symposium
    Surface Science Division Friday Sessions
       Session SS3+EM-FrM

Paper SS3+EM-FrM8
Ab initio Study of Adsorption and Decomposition of NH@sub 3@ on Si(100)-(2x1)

Friday, October 29, 1999, 10:40 am, Room 604

Session: Reactions on Semiconductors
Presenter: Y. Widjaja, Stanford University
Authors: Y. Widjaja, Stanford University
M. Mysinger, Stanford University
C. Musgrave, Stanford University
Correspondent: Click to Email
Deposition of silicon nitride thin films has become a key technology in the microelectronics industry. In silicon nitride deposition, NH@sub 3@ is typically used as the nitriding agent because of its high sticking coefficient and reactivity. In this study, we investigate the atomistic mechanisms for NH@sub 3@ adsorption and initial decomposition on the (2x1) reconstructed Si(100) surface using B3LYP density functional theory (DFT) and by utilizing the cluster model. We present a detailed investigation of the effects of cluster size on the reaction energetics. We find that the Si@sub 9@H@sub 12@ (1-dimer) cluster model does not describe the NH@sub 3@(a) adsorption state well due to the delocalized nature of the electron transfer in forming the NH@sub 3@(a) dative bond. We find that the Si@sub 21@H@sub 20@ (3-dimer) cluster is necessary to fully capture these non-local effects. The 3-dimer model is able to satisfactorily reproduce the results of larger cluster models. We then use the 3-dimer cluster model to study the adsorption and decomposition reactions of NH@sub 3@ on the Si(100)-(2x1) surface. Ammonia is found to adsorb on the down atom of buckled silicon dimers with no activation barrier. This adsorption is exothermic with an adsorption energy of 29 kcal/mol. This adsorption is then followed by dissociation to form NH@sub 2@(a) + H(a) with a low activation energy. Our calculated recombination desorption energy of 51 kcal/mol is found to be in good agreement with the TPD experimental result of 47 kcal/mol. In addition, we also calculate the vibrational spectra of the dissociated species. We find our results to be in good agreement with the experimental HREELS spectra.