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High quality diamond thin films were deposited on different substrates at temperatures from 300 to 1000 °C by the microwave plasma enhanced chemical vapor deposition (MPCVD) system. The quality of deposited diamond films was improved by adding oxygen in the gas mixtures. Different ratios of methane to oxygen concentration in hydrogen at different temperatures have been studied. At high temperatures (800-1000 °C), the addition of oxygen will not only enhance the growth rate of deposited films but also extend the region of diamond formation. At low temperatures (900 °C) were either graphitic or diamond containing a large amount of graphitic or amorphous carbon and at low temperatures (800 OC).4"9 The importance of the additive at low temperatures (600 °C) were usually gray in color on silicon TABLE I. Deposition conditions.

CO

Microwave power (W)

Total pressure (Torr)

1000 800 600 500 400 300

1000 800 500 400 300 260

50 34 20 14 10 6

Temperature

2306

http://journals.cambridge.org

substrates. The darkness of these gray films changed with different ratios of methane to oxygen concentration in the feed gas mixtures being used. The gray color of films on silicon was believed to be the color of the silicon carbide forming between the silicon substrate and the diamond film. Increasing the concentration of methane in the feed gas mixtures increased the graphitic component in the film, which made the film darker in color. With higher concentrations of oxygen in the same methane-hydrogen feed gas mixtures, less graphitic component and better quality of diamond in the film made the film lighter gray in color. At low temperatures (