| Summary: | 碩士 === 國立交通大學 === 材料科學與工程研究所 === 84 === Diamond films were deposited on P-type (100) silicon
substrate by a hot filament chemical vapor deposition (HFCVD)
system with reactant gases of CH4 and H2. Effects of CH4/H2
ratio, deposition time, deposition temperature and substrate
pretreatment on residual stress and optical properties of films
were investigated. The FTIR transmission spectra and their
mathematical transmission modeling were used to analyze the
infrared optical properties. The films were also characterized
by SEM, Raman and XRD. The internal stresses of the films were
estimated by Raman spectroscopy and X-ray diffraction, and the
d-spacings of the crystal planes were rectified by the Rietveld
analysis method. The purposes of this work were to investigate
the optical properties and the origins of internal stress of
diamond films, and to correlate the internal stress with the
optical properties.
The experimental results indicate that the origins of the
residual stress of diamond films are mainly the thermal stress
and the intrinsic stress. The internal stresses on Si(100)
wafrs are ranging from -1.234 to -6.204 GPa, as determined by X-
ray diffraction method, and from -0.729 to -2.609 GPa, as
determined by Raman spectroscopy. The difference in stress
level may be partly due to a limited penetration depth of laser
beam in Raman spectroscope. The results also show that a higher
non-diamond carbon content in the diamond crystal, not at the
grain boundaries, will result in a higher compressive intrinsic
stress. The deposition conditions which can cause an increase
in non-diamond carbon content in the films, will result in an
increase in compressive stress, such as, higher CH4/H2 ratios,
or lower deposition temperatures, The results also indicate
that the internal stresses at the thickness around 4-5um show a
minimum value, and show a maximum value around 10-12um
thickness. This is due to the fact that the maximum internal
stress was companied by the renucleation phenomena, which result
in an increase in non-diamond carbon content in the films.
For optical properties, the results reveal that the refractive
indexes of the films vary from 2.33 to 2.50, depending on
wavelength and non-diamond carbon content. Alonger wavelength
and a higher non-diamond carbon content will result in a lower
refractive index. The optical transmittance of the films is
depending mainly on the surface roughness and non-diamond carbon
content, and slightly on the film thickness, and is ranging
from 42-48% with the roughness of 0.15-0.2um and thickness
10.8-23.6um. The C-H stretching absorptions were found in the
transmission spectra at higher thicknesses and lower
wavelengths, indicating a high hydrogen content in the films.
It is noted that a lower internal stress of the film will tend
to have a higher refractive index.
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