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.
Manipulation and Control of Nucleation and Growth Kinetics with Hydrogen Dilution in Hot-Wire CVD Growth of Poly-Si
We systematically explore the relationship between gas-phase kinetics and film microstructure in the hot-wire CVD technique using diluted silane (1% in He) and additional hydrogen. Using a wire temperature of 2000°C, films were grown on Si (100) at 300°C using 1 mTorr SiH 4 and 99 mTorr He at hydrogen pressures from 0-100 mTorr. Transmission electron microscopy and atomic force microscopy measurements indicated that continuous microcrystalline films had a columnar grain structure and that grain size increased from 40 nm using SiH 4 /He to 85 nm using SiH 4 /He/H 2 with 20:1 H 2 :SiH 4 ratio due to the etching of silicon by hydrogen. Etching rate measurements using a quartz deposition monitor show that, under the current deposition conditions, a transition from net film growth (0.17 nm/s using only SiH 4 ) to net etching occurs at a H 2 :SiH 4 ration of 80:1. The effect of atomic H on the nucleation density during the initial stages of growth has also been investigated, revealing a sublinear dependence of nucleation density with time and a decrease in nucleation density with increasing H 2 dilution. High deposition rate growth with no H 2 dilution has been achieved on a low-density array of seed nuclei produced using high H 2 dilution.
Selective silicon epitaxy by photo-chemical vapor deposition at a very low temperature of 160°C
We have grown epitaxial Si films by the photo-chemical vapor deposition (photo-CVD) technique with SiH4 and H2 at a very low-temperature of 160°C. Epitaxial films were grown on silicon substrates, while amorphous-like films were deposited on glass substrates. Furthermore, it was found from the atomic hydrogen etching which was produced by photo-dissociation of hydrogen that the etching rate of amorphous silicon was much higher than that of crystal silicon. By using these selectively, we have demonstrated selective epitaxial growth of silicon by the photo-CVD technique followed by the atomic hydrogen photo-etching. Furthermore, heavily phosphorus-doped silicon films (>1 × 1021 cm1−3) were also selectively grown by this novel technique.