The growth of highly oriented diamond is performed on Si (111) and 6H-SiC (0001) substrates via two-step and three-step processes using microwave plasma CVD. The two-step process involves bias-enhanced nucleation (BEN) and deposition, and the three-step process involves carburization in addition to the two-step process. The diamond films grown on the Si (111) substrate exhibit high quality and desirable (111)-orientation under the carburization condition of 5.3 X 10(3) Pa in pressure with no bias applied. The mechanism for the formation of conversion layer during the carburization step is investigated on both the substrates through the Raman and X-ray photoelectron spectroscopy (XPS) studies. The results indicate that the carburization mainly composed of beta-SiC, which plays a crucial role for the formation of the conversion layer and which eventually promotes the diamond nucleation. It is also suggested that a highly-oriented and high-quality diamond film can be successfully achieved by carburization. (C) 2003 Elsevier B.V. All rights reserved.