AMORPHOUS AND MICROCRYSTALLINE SILICON FILMS DEPOSITED BY HOT-WIRE CHEMICAL-VAPOR-DEPOSITION AT FILAMENT TEMPERATURES BETWEEN 1500-DEGREES-C AND 1900-DEGREES-C
P. Brogueira et al., AMORPHOUS AND MICROCRYSTALLINE SILICON FILMS DEPOSITED BY HOT-WIRE CHEMICAL-VAPOR-DEPOSITION AT FILAMENT TEMPERATURES BETWEEN 1500-DEGREES-C AND 1900-DEGREES-C, Journal of applied physics, 79(11), 1996, pp. 8748-8760
The optical, electronic and structural properties of thin films deposi
ted by Hot-wire chemical vapor deposition with filament temperatures,
T-fil, between 1500 and 1900 degrees C from silane and hydrogen are st
udied. The substrate temperature, T-sub, was kept constant at 220 degr
ees 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(Si
H4)less than or equal to 1). At these deposition conditions, high grow
th rates are observed (r(d) greater than or equal to 10 Angstrom s(-1)
) both with and without hydrogen dilution, and no silicon deposition w
as 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 decrea
sed from above 0.3 Torr to below 0.1 Torr. The highest dark conductivi
ty 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 hyd
rogen dilution, for substrate temperatures as low as similar to 150 de
grees C, and for very thin films (similar to 0.05 mu m). Silicon growt
h on the filaments is observed. For both T-fil regimes, an amorphous t
o microcrystalline transition is also observed when the hydrogen dilut
ion 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 o
f atomic hydrogen and the concentration of the precursor to silicon de
position (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 In
stitute of Physics.