AVS 46th International Symposium
    Plasma Science and Technology Division Monday Sessions
       Session PS-MoP

Paper PS-MoP28
Atomistic Simulations of Radical-Surface Interactions during Plasma-Enhanced Chemical Vapor Deposition of Si Films from Silane/Hydrogen Discharges

Monday, October 25, 1999, 5:30 pm, Room 4C

Session: Poster Session
Presenter: D. Maroudas, 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
S.P. Walch, NASA Ames Research Center
Correspondent: Click to Email
Hydrogenated amorphous silicon (a-Si:H) films grown by deposition through silane-containing plasmas are widely used in solar cells and thin film transistors for flat panel displays. We present a study of the interactions of reactive radicals originating in the plasma with Si surfaces during plasma deposition from SiH@sub 4@/H@sub 2@ discharges based on recently developed classical force fields and ab initio calculations within density functional theory. Our simulation study employs a hierarchical approach that combines molecular-dynamics (MD) simulations for reaction identification and mechanistic understanding aided by molecular-statics and Monte Carlo simulations for reaction analysis. Interactions with isolated radicals during the initial stage of growth for each surface at submonolayer coverage are studied in detail to determine the surface chemical reactivity and the implications for the deposited film properties. The adsorption sites for the SiH@sub x@ (x=1,2,3) radicals are identified on the pristine and H-terminated Si(001)-(2X1) surfaces: the energetics of adsorption determined by the classical potential agree well with ab initio calculations. In addition, ultra-fast rate deposition of a-Si:H from each of the SiH@sub x@ radicals has been simulated through MD by repeatedly impinging the corresponding radical onto H-terminated Si(001)-(2X1) surfaces. SiH@sub 3@ radicals can abstract H atoms from the surface through an Eley-Rideal mechanism and return to the gas phase as silane molecules. Silyl radicals also can attach dissociatively onto the H-terminated Si surface at the dimer bond center. This insertion reaction leads to breaking of the dimer bond and subsequent transfer of a H atom from the radical to one of the dimer atoms resulting in the formation of two surface dihydride species. The energetics of this reaction is analyzed in detail both with classical and ab initio calculations. The theoretical results are compared with experimental observations.