OES study of the plasma during CVD diamond growth using CCl 4 /H 2 /O 2 mixtures

Abstract

Abstract Generation of atomic hydrogen in H2/Ar/CCl4 microwave discharges with O2 addition has been investigated. In situ mass spectrometry and emission hydrogen-atom actinometry have been used in the microwave-plasma-assisted chemical vapor deposition (MWPACVD) reactor. Optical emission spectroscopy (OES) was used to study the intensity of Hα, Hβ and Hγ lines using argon as actinometer. The results showed different increases in the atomic hydrogen concentration for the three hydrogen lines analyzed for additions of up to 1.5% CCl4. These results confirm a previous study on the validity of the OES technique using the Hγ line intensity. An additional increase in the atomic hydrogen generation was also observed when O2 was added to the H2/CCl4 mixtures. Chemical reaction products, detected by exhaust-gas mass spectrometry, showed that CCl4 is completely dissociated in the plasma reactor with a fast conversion into hydrocarbons. The effects of O2 addition lead an increase in CO and H2O formation associated with a decrease in CH4 and C2H2 concentration. Oxygen decreases the hydrocarbon concentration for high concentrations of halogenated precursor. This behavior inhibits the formation of solid carbon observed in mixtures with chlorine and permits the production of good-quality CVD diamond films owing to the high generation of atomic hydrogen. The films grown in different concentrations of CCl4 and O2 were analyzed by scanning electron microscopy and Raman spectroscopy.