Quantitative modelling of nucleation kinetics in experiments for poly-Si growth on SiO2 by hot wire chemical vapor deposition
Abstract We apply a rate-equation pair binding model of nucleation kinetics to the nucleation of Si islands grown by hot wire chemical vapor deposition on SiO 2 substrates. The grain size of poly-Si films increases with H 2 dilution, which is attributed to atomic H etching of Si monomers rather than stable Si clusters during the early stages of nucleation. The nucleation density increases sublinearly with time at low coverage, implying a fast nucleation rate until a critical density is reached, after which grain growth begins. The nucleation density decreases with increasing H 2 dilution (H 2 :SiH 4 ) due to etching, and with increasing temperature, due to enhanced Si monomer diffusivity on SiO 2 . From temperature-dependent measurements, we estimate the activation energy for surface diffusion of Si monomers on SiO 2 to be 0.47±0.09 eV. Simulations of the temperature-dependent supercritical cluster density lead to an estimated activation energy of 0.42±0.01 eV and an estimated surface diffusion coefficient prefactor of 0.1±0.03 cm 2 /s.
Polycrystalline silicon films obtained by hot-wire chemical vapour deposition
Silicon films were deposited at moderate substrate temperatures (280–500° C) from pure silane and a silane-hydrogen mixture (10% SiH4, 90% H2) in a hotwire CVD reactor. The morphology, structure and composition of the samples were studied with scanning electron microscopy, transmission electron microscopy, transmission electron diffraction, X-ray diffraction, Raman spectroscopy and secondary ion mass spectrometry. The sample deposited at 500° C with pure silane has an amorphous structure, whereas the samples obtained from silane diluted in hydrogen have a polycrystalline structure, even that grown at the lowest temperature (280° C). Polycrystalline samples have a columnar structure with 0.3–1 μm crystallite sizes with preferential orientation in [220] direction. Deposition rates depend on the filament-substrate distance and range from 9.5 to 37 Å/s for the polycrystalline samples. The high quality of the polycrystalline samples obtained makes the hot-wire technique very promising. Moreover, it is expected to be easily scaled up for applications to large-area optoelectronic devices and to photovoltaic solar cells.
Silicon epitaxy on hydrogen-terminated Si(001) surfaces using thermal and energetic beams
Abstract Silicon epitaxy on hydrogen-terminated Si(001) surfaces has been studied using molecular dynamics simulations. Epitaxy on the dihydride-terminated Si(001)-(1 × 1) surface is inhibited for Si atoms at thermal energies due to strain hindrances created by hydrogen. At greater incident Si atom energies (2–10 eV), epitaxy proceeds primarily through “subplantation”, i.e. subsurface implantation of the incident Si atom accompanied by segregation of SiH 2 during growth. The subplantation probability rises very rapidly with the incident-atom energy, a result which is consistent with the observation of epitaxial film growth on dihyride-terminated Si(001) by sputter deposition when under similar conditions conventional molecular beam epitaxy results in amorphous Si growth. On the hydrogen-terminated Si(001)-(2 × 1) surface, the simulation results suggest that both subplantation and hydrogen atom transfer to the incident Si atom are possible routes to epitaxy.