Continuum Spectrum in Diamond Deposition: Carbon Nanoparticles and Gas Temperature Monitoring

One of the most effective tools for depositing high-quality diamond films is plasma-enhanced chemical vapor deposition using microwave discharge. This paper examines the presence of an intense continuous spectrum in the radiation of such a plasma, the shape of which is similar to the Planck spectrum. It has been shown that the source of this radiation can be carbon nanoparticles, hypothetically present in the plasma volume. The temperature of the particles in the center of the plasma, estimated from the position of the maximum of the continuous spectrum, turned out to be about 2600 K, which, within the error limits, coincides with the gas temperature. Spatial measurements of both temperatures showed that the particles are in local thermodynamic equilibrium with the gas throughout the plasma volume. The spatial temperature profile of the particles shows a uniform zone with a radius of about 1 cm in the center of the discharge, the boundaries of which correspond to the region of uniform growth of the diamond film, both in thickness and in structure. The relationship between continuous emission of carbon particles in plasma and the homogeneity of growth conditions opens the possibility of using near-infrared spectroscopy for real-time monitoring of key parameters of the deposition process, which can be used to improve the reproducibility of the synthesis of high-quality diamond films.