Characterization of the diamond growth process using optical emission spectroscopy

Abstract

In situ optical emission spectroscopy was applied to an electron assisted hot filament diamond growth process. Emission lines from the Balmer series of atomic hydrogen, molecular hydrogen, CH, CH+, and Ar were observed in the visible range when CH4, Ar, and H2 were used as the input gases. The relative concentration of atomic hydrogen was estimated by using the emission line of Ar at 750.4 nm as an actinometer. The effects of deposition conditions, including filament temperature, substrate temperature, bias voltage, and methane concentration in the source gas, on the species distribution, electron temperature, and diamond film growth were investigated. The vertical spatially resolved measurements show that the concentration of atomic hydrogen decreases as the detection point moves far from the filament and suddenly drops near the substrate. The horizontal spatially resolved measurements show that the homogeneous region of reaction species and the electron temperature near the substrate define the homogeneous region of diamond film growth. Increase of filament temperature, substrate temperature, bias voltage, and the decrease of methane concentration in the feed gas increase the atomic hydrogen concentration and diamond deposition. A higher intensity ratio of CH+ to Ar and a lower ratio of CH to Ar are associated with a high quality of diamond film growth. Optical emission spectroscopy showed that atomic hydrogen and CH+ correlate with the formation of the diamond component, whereas the CH relates to the presence of amorphous carbon in the films. The effect of positive bias on the diamond growth results largely from the bombardment of electrons on the substrate.