AVS 51st International Symposium
    Plasma Science and Technology Thursday Sessions
       Session PS-ThA

Paper PS-ThA7
First-Principles Analysis of Precursor-Surface Interactions Relevant to Plasma Deposition of Silicon Thin Films

Thursday, November 18, 2004, 4:00 pm, Room 213A

Session: Plasma-Surface Interaction
Presenter: T. Bakos, University of Massachusetts
Authors: T. Bakos, University of Massachusetts
D. Maroudas, University of Massachusetts
Correspondent: Click to Email
Plasma-enhanced chemical vapor deposition is used widely for growing hydrogenated amorphous silicon (a-Si:H) thin films for electronic, optoelectronic, and photovoltaic applications. Plasma deposited film properties, such as H content, crystallinity, and surface roughness, depend on the identities and fluxes of reactive radicals impinging on the deposition surface and on the corresponding radical-surface interaction mechanisms. In this presentation, we report results of first-principles density functional theory (DFT) calculations that elucidate the reaction pathways and energetics of key reactions with the H-terminated Si(100)-(2x1) surface of the SiH@sub 3@ radical, the dominant precursor for deposition of device-quality a-Si:H films. In particular, we have found that SiH@sub 3@ can insert into surface Si-Si dimer bonds, abstract H from surface Si atoms through an Eley-Rideal (ER) mechanism and passivate surface dangling bonds in exothermic and barrierless reactions. In all of these cases, we have determined the optimal reaction pathways and the corresponding transition states based on accurate, well-converged total-energy calculations and implementing the nudged elastic band method. The theoretically predicted energetics of radical insertion, H abstraction, and passivation reactions are consistent with the experimentally observed temperature independence of the SiH@sub 3@ surface reactivity during plasma deposition of a-Si:H films. In addition to the ER mechanism, we have identified a Langmuir-Hinshelwood mechanism of surface H abstraction with a moderate energy barrier that may be responsible for reducing the H content of films deposited at high temperatures. Reactions similar to those analyzed by DFT on the Si(100)-(2x1):H surface also are observed in molecular-dynamics simulations of a-Si:H thin film growth. Therefore, our electronic-structure analysis also can be considered as representative of surface reactions occurring on a-Si growth surfaces.