Atomic-Scale Analysis of Plasma-Enhanced Chemical Vapor Deposition from SiH 4 / 2 Plasmas on Si Substrates
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surfaces are shown in Figs. la and lb. The dynamics of the interaction of Sill3 with the surfaces described above was simulated by numerical integration of the classical equations of motion according to the interatomic forces derived from the extended Tersoff potential [8,9]. In the MD simulations of radical impingement on each of the surfaces, the location of impingement on the surface, the molecular orientation of the radical with respect to the surface, the temperature of the sample, and the kinetic energy of the radical were the specified parameters. RESULTS AND DISCUSSION The reactivity of Sill3 radical impinging on the surface in a particular orientation at a given location is best characterized through the magnitude of the energy gained upon interaction of the radical with the surface at that location. This energy gain was calculated over a grid of locations on each of the surfaces and used to generate reactivity maps [8,9]. The reactivity maps for the SiH 3 radical impinging with its dangling bond pointing towards the surface are shown in Figs. lc and Id for the pristine and H-terminated Si(001)-(2x 1) surfaces, respectively. On these maps, darker regions correspond to greater energy gain upon interaction of the Sill3 radical with the surface than lighter regions and, hence, correspond to more reactive regions. The least reactive regions on the pristine Si(001)-(2xl) surface for Sill 3 impinging in the Si-down configuration (with the Si atom of the radical closer to the surface) are the locations in the troughs between dimer rows; in contrast, regions of the surface near the dangling bonds inside the dimer rows are more reactive. Clearly, Fig. ic shows that on the pristine Si(001)-(2xl) surface, there is a predominance of sites that are energetically favorable for adsorption of the Sill3 radical. For the case of Sill3 impinging on the corresponding H-terminated surface, the overall reactivity of the surface is reduced significantly. The presence of the H between the Si atoms of the surface and the radical acts as a shield, which reduces the driving force for Si-Si bond formation. The only reactive regions on the surface lie close to the Si-H bonds which suggests a possibility of the Si-H bond being broken and the H atom abstracted under favorable conditions of Sill3 radical impingement. During the initial stages of growth on the pristine and H-terminated Si(001)-(2xl) surfaces, the Sill3 radical impinges on the surfaces shown in Figs. la and 1b, respectively. MD simulations were conducted where Sill3 radicals impinged on the six high-symmetry locations of the ordered crystalline surface shown in Fig. 1 in both Si-down and H-down radical orientations for both the pristine and H-terminated Si(001)-(2xl) surfaces: during these simulations, the surfaces were maintained at 300 K and the radicals were directed towards the surface with an initial kinetic energy corresponding to 300 K. The Sill3 radical was most reactive when it impinged on the pristine Si(001)-(2xl) surface, immediately forming bonds with the dan
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