Amorphous and microcrystalline silicon films deposited by hot-wire chemical vapor deposition at filament temperatures between 1500 and 1900 degrees C

The optical, electronic and structural properties of thin films deposited by Hot-wire chemical vapor deposition with filament temperatures, T-fil, between 1500 and 1900 degrees C from silane and hydrogen are studied. The substrate temperature, T-sub, was kept constant at 220 degrees C. Amorphous silicon films (a-Si:H) are obtained at high filament temperatures, low deposition pressures and low hydrogen-to-silane flow rate ratio (T(fil)similar to 1900 degrees C, p<30 mTorr and F-H2/F(SiH4)less than or equal to 1). At these deposition conditions, high growth rates are observed (r(d) greater than or equal to 10 Angstrom s(-1)) both with and without hydrogen dilution, and no silicon deposition was observed on the filaments. However, if a lower filament temperature is used (T(fil)similar to 1500 degrees C) a transition from a-Si:H to microcrystalline silicon (mu c-Si:H) occurs as the pressure is decreased from above 0.3 Torr to below 0.1 Torr. The highest dark conductivity and lowest activation energy, of similar to 1 Scm(-1) and <0.1 eV, respectively, were observed for mu c-Si:H deposited at p similar to 50 mTorr. In this T-fil regime, mu c-Si:H growth is achieved without hydrogen dilution, for substrate temperatures as low as similar to 150 degrees C, and for very thin films (similar to 0.05 mu m). Silicon growth on the filaments is observed. For both T-fil regimes, an amorphous to microcrystalline transition is also observed when the hydrogen dilution is increased (F-H2/F-SiH4>4). A kinetic growth model is developed, which suggests that the transition from amorphous to microcrystalline can be explained by considering a balance between the concentration of atomic hydrogen and the concentration of the precursor to silicon deposition (SixHz with z less than or equal to 3x) near the sample. This concentration ratio is shown to be controlled both by the deposition pressure, p, and the filament temperature, T-fil. (C) 1996 American Institute of Physics.