AVS 46th International Symposium
    Plasma Science and Technology Division Thursday Sessions
       Session PS-ThM

Paper PS-ThM1
Theoretical Analysis of the Interactions of Chemically Reactive Clusters from Silane Plasmas with Crystalline and Amorphous Silicon Surfaces

Thursday, October 28, 1999, 8:20 am, Room 609

Session: Plasma-Surface Interactions II
Presenter: S. Ramalingam, University of California, Santa Barbara
Authors: S. Ramalingam, University of California, Santa Barbara
E.S. Aydil, University of California, Santa Barbara
D. Maroudas, University of California, Santa Barbara
W.M.M. Kessels, Eindhoven University of Technology, The Netherlands
Correspondent: Click to Email
Silane containing discharges are used commonly for depositing hydrogenated amorphous silicon (a-Si:H). The structure and electronic properties of the film are determined by the identities and fluxes of the species that impinge and react on the deposition surface. In this presentation, we focus on the interactions with Si surfaces of bare and hydrogenated Si clusters, which can be present in significant concentrations in the plasma. We have conducted a systematic analysis, through classical molecular dynamics (MD) simulations, to study the interactions of Si@sub n@H@sub y@ clusters originating in a SiH@sub 4@ discharge with pristine and H-terminated crystalline Si (c-Si) surfaces and a-Si:H deposited on c-Si. The investigated parameters include the molecular orientation of the cluster, the impingement location on the surface, the kinetic energy of the impinging cluster, and the substrate temperature. The structures and energetics of the Si@sub n@H@sub y@ clusters predicted by the empirical interatomic potential are in good agreement with ab initio results available in the literature. The MD simulations show that the clusters react with unit probability on the pristine Si(001)-(2X1) surface and with nearly unit probability on the H-terminated Si(001)-(2X1) surface. The clusters distort considerably upon attachment to the surface. For example, the Si@sub 6@H@sub 13@ cluster contains a two-fold coordinated H atom, which frequently loses one of its bonds with a Si atom upon reaction with the surface. This leads to the formation of brush-like configurations on the surface of the film, which often collapse on the surface to form more compact structures. The high reactivity of these clusters with Si surfaces and their distortion upon reaction with the surface are explained by the strained nature of the bonds in the original gas-phase clusters. The Si atoms of the cluster often attach preferentially at the center of the dimer bond, and either weaken or break this bond.