AVS 45th International Symposium
    Plasma Science and Technology Division Wednesday Sessions
       Session PS-WeA

Paper PS-WeA1
Surface Reactions and Hydrogen Coverage on Plasma Deposited Hydrogenated Amorphous Silicon and Nanocrystalline Silicon Surfaces

Wednesday, November 4, 1998, 2:00 pm, Room 318/319/320

Session: Plasma-Surface Interactions I
Presenter: D.C. Marra, University of California, Santa Barbara
Authors: D.C. Marra, University of California, Santa Barbara
S. Ramalingam, University of California, Santa Barbara
E. Edelberg, University of California, Santa Barbara
D. Maroudas, University of California, Santa Barbara
E.S. Aydil, University of California, Santa Barbara
Correspondent: Click to Email
In situ attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy was used to study the H bonding on surfaces of amorphous hydrogenated silicon (a-Si:H) and nanocrystalline (nc-Si:H) films during plasma enhanced chemical vapor deposition (PECVD) from SiH@sub 4@/H@sub 2@/Ar containing discharges. During the deposition of a-Si:H films using SiH@sub 4@ without H@sub 2@ dilution, the surface coverage was primarily di- and trihydrides, and there were very few dangling bonds on the surface. In contrast, during the deposition of nc-Si:H using SiH@sub 4@ diluted with H@sub 2@, the amount of di- and trihydrides on the surface was drastically reduced and monohydrides dominated the surface. Furthermore, the vibrational frequencies of the monohydrides on nc-Si:H film match well with the resonant frequencies of monohydrides on H-terminated Si(111) and Si(001) surfaces. The decrease of higher hydrides upon H@sub 2@ dilution is attributed to an enhanced dissociation rate of tri- and di-hydrides on the surface through dangling bonds created by increased rate of H abstraction from the surface. The mechanism of hydrogen loss from the surface is thought to be abstraction by H and/or SiH@sub 3@ radicals. Simultaneously with the experiments, we have been using molecular dynamics (MD) simulations of radical-surface interactions occurring during PECVD of Si films. The MD simulations aim at the direct examination of chemical reactions, such as H abstraction by SiH@sub 3@ and by H as suggested by the analysis of the ATR-FTIR experiments. For example, using the MD simulations of deposition through SiH@sub 3@ impingement on the surface, we have observed that the dominant mechanism of H removal from the surface is through abstraction by SiH@sub 3@ radicals, which return subsequently to the gas phase in the form of silane. Atomistic simulation results will be presented together with experimental evidence for reactions that are thought to play key roles in plasma deposition of Si films.