Investigation of the nucleation mechanism in bias-enhanced diamond deposition

Polycrystalline diamond films were deposited in a MW-PECVD reactor employing bias-enhanced nucleation as pretreatment to promote the subsequent diamond nucleation. The substrate temperature during the bias-enhanced nucleation was varied between 600 degrees and 760 degrees C by external heating, while the other deposition parameters namely the microwave input power were kept constant. Likewise, the deposition parameters were not changed in the subsequent diamond growth period throughout the experiment. The films formed during the bias-enhanced nucleation were analyzed employing electron energy loss spectroscopy (EELS) and scanning electron microscopy (SEM). The nuclei density (N-D) obtained for good quality diamond crystals after the nucleation step and an additional growth period increases considerably from 1X10(6) cm(-2) or less to 1X10(10) cm(-2) in a narrow temperature range between 670 and 700 degrees C. For temperatures exceeding 700 degrees C continuous films are formed. The structure of the pretreatment deposit also undergoes considerable changes: the intensity of the diamond plasmon increases with the substrate temperature, which is indicative of an increase in the concentration of diamond crystallites embedded in an otherwise amorphous carbon matrix. Our experiments suggest that diamond crystallites formed during the pretreatment serve as nucleation centers for the subsequent diamond growth. We can also conclude that the variation in the substrate temperature rather than the changes in the microwave input power or, respectively, plasma chemistry, drive the observed structural changes and increase in N-D. (C) 1996 American Institute of Physics.