Method and apparatus for in-situ measuring filament temperature and the thickness of a diamond
Reference Number: N 03-03
Inventors: Wu, Ching-Hsong; Potter, Timothy J.; Tamor, Michael A.
Owner: NISTAC
USPTO Link:5240736
Invention Summary
The invention of Applicants discloses a simple and inexpensive method and apparatus
for the concurrent in-situ monitoring of both filament temperature and the thickness
of a film deposited on a substrate disposed within a hot-filament chemical vapor deposition
reactor. Generally, Applicants disclose the use of a single optical thermometer coupled
with a lightpipe which obviates the need for focusing optics and an external light
source.
In operation, white light emitted directly from the filament and that reflected from
the top and bottom surfaces of the deposited film are collected and converted to monochromatic
light through the use of simple narrow-band interference filters operative over specific,
yet different optical bandwidths. This information is thereafter used to mathematically
calculate the filament temperature and film thickness.
It is therefore a general object of the present invention to provide a simple, inexpensive
method and apparatus for the concurrent in-situ measurement of filament temperature
and film thickness or growth rate.
A more specific object of the present invention is the provision of a simple and
inexpensive method and apparatus for the measurement and control of filament temperature
and diamond film thickness in a hot-filament chemical vapor deposition reactor.
In accordance with the apparatus disclosed by Applicants herein, there is provided
heating means positioned within a hot-filament chemical vapor deposition reactor for
maintaining a film substrate at a selected fixed temperature. Radiation detection
means is further provided for detecting radiation emitted from the filament and radiation
reflected as an interference fringe from the top and bottom surfaces of the film grown
on the substrate during operation of the reactor. Power supply means is also provided
in electrical contact with the radiation detection means and the filament for regulating
the temperature thereof.
First signal generating means is provided in electrical contact with the radiation
detection means for receiving radiation over a first selected optical bandwidth and
generating a first electrical signal having a current corresponding to the intensity
of the detected radiation. Second signal generating means is also provided in electrical
contact with the radiation detection means for receiving radiation over a second selected
optical bandwidth and generating a second electrical signal having a current corresponding
to the intensity of the detected radiation. Finally, signal processing means is provided
in electrical contact with the first and second signal generating means for receiving
and processing the first and second electrical signals to mathematically calculate
the instantaneous temperature of the filament and the thickness of the film grown
on the substrate during deposition.
The operation of the apparatus disclosed by Applicant is more fully described as
follows. First, the film substrate must be heated to a selected fixed temperature.
Thereafter, radiation emitted from the filament and radiation reflected as an interference
fringe from the top and bottom surfaces of the diamond film is detected over a first
selected optical bandwidth. This radiation is concurrently detected over a second
selected optical bandwidth. Thereafter, first and second electrical signals are generated,
each having a current corresponding to the intensity of the radiation detected over
the corresponding selected optical bandwidth. The first and second electrical signals
are compared to determine the ratio of the respective currents such that the filament
temperature may be mathematically calculated.
Concurrently therewith, the period of interference fringe may be calculated such
that the diamond film thickness (D) may be determined in accordance with the formulas
D=nP and P=.lambda./2.eta. where P is the film thickness corresponding to one period
of interference fringe, .lambda. is the wavelength of the first or second optical
bandwidths, .eta. is the index of refraction and n is the number of the period of
interference fringes. The growth rate (R) of the deposited film may also be calculated
according to the formula ##EQU1## where t=deposition time.
If it is desired by the operator to control the filament temperature based upon the
information provided, a third electrical signal may be generated corresponding to
the calculated filament temperature and directed to a control means for adjusting
the power means to achieve the desired chemical composition of the depositing gas.