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Institute for Commercialization

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.