Characterization of dual hollow cathode arc chemical vapor deposition by optical emission spectroscopy

Optical emission spectroscopy (OES) using Ar actinometry is employed to characterize plasma in a dual hollow cathode arc chemical vapor deposition system to study the effect of electron bombardment on diamond growth. Using OES, it was found that the H atom concentration (H_α/Ar) and the electron temperature (H_β/H_α) increase significantly in the substrate current below a threshold, and become insensitive to the substrate current above the threshold. In contrast, the growth rate is almost constant below the threshold and increases significantly with the substrate current above the threshold. It is concluded that increasing the substrate current to below the threshold first shifts the plasma to the substrate, and then, increasing the current above the threshold increases electron bombardment onto the surface only. The greatly enhanced growth rate above the threshold is mainly due to surface activation by electron bombardment. Electron bombardment evidently replaces some functions of H atoms in diamond growth. OES results also show that H concentration is high and electron temperature is low in the growth using CHCl₃, compared with that using CH₄. The possible reasons for and effects of CHCl₃ on the higher growth rate and poorer film quality are discussed.