Growth of filmy diamond crystals has been strongly desired, and the plasma CVD is expected as one of the growth techniques which provide high quality crystalline diamond films. This study deals with the growth of uniform crystalline diamond films by means of the plasma CVD. The main stress was laid on the effects of the surface treatments of the silicon substrate and the substrate potential on composition of deposited materials as well as on the morphology of diamond crystals grown on the substrate. A mixture of methane (1%)/hydrogen with a pressure to 400 Pa was flown at a rate of 150 cc/min and was discharged by applying 200 W, 2.45 GHz microwave power. The Si substrates were heated to 850 ° C. Nuclei for the diamond crystal growth were preferentially generated on the defect sites caused by the surface treatments. With increasing the substrate potential in the negative direction, the growth of silicon carbide was observed to increase. When the substrate was positively biased, filmy diamond layers were found to be deposited.