Effect of amorphous carbon film structure on diamond nucleation

Abstract

The effect of the structure of amorphous carbon films on diamond nucleation was investigated with a microwave plasma-enhanced chemical-vapor-deposition system. The films were synthesized on smooth silicon surfaces using a vacuum arc technique. Different film structures were obtained by varying the negative pulsed bias voltage from approximately zero to −1.0 kV. The maximum film density and etching resistance in a pure hydrogen plasma were obtained for a pulsed bias voltage equal to −200 V. It was determined that these films contained the highest percentage of tetrahedrally bonded (sp3) atomic carbon configurations. The carbon-coated substrates were first exposed to a low-temperature high-methane-concentration hydrogen plasma before initiating the diamond nucleation experiments. The higher nucleation density (∼3×109 cm−2) and better quality of diamond films corresponded to a pulsed bias voltage of −200 V. Increasing the magnitude of the negative pulsed bias voltage resulted in significantly lower nucleation densities and the formation of relatively larger particles. The enhancement of the diamond nucleation density for a pulsed bias voltage of −200 V is attributed to both the inherent high etching resistance of the produced amorphous carbon films, resulting from the high content of sp3 bonds, and the pretreatment process which yielded a high density of high-surface free-energy nucleation sites.