Diamond deposition with chlorinated methanes: investigation of the plasma chemistry

Methane and chlorinated methanes (CH4, CH3Cl, CH2Cl2, CHCl3, CCl4) were diluted in hydrogen and were decomposed in an electrodeless pulsed RF discharge sustained in a quartz glass tube. From the active plasma zone a small amount of the process gas was extracted by a helium flushed probe system, transported to and detected by a calibrated quadrupole mass spectrometer. The gas phase chemistry in the reactor was also modelled by CHEMKIN computer code. A reaction mechanism for the CHCl system, which consists of 158 reactions and 40 species, was used to model the complex plasma chemistry. It turned out that in the plasma the chlorinated methanes are decomposed very quickly to the main stable species HCl, CH4 and C2H2. Chlorinated hydrocarbon radicals are only present within a few millisecond after the initial contact of the precursor with the plasma. At steady state, the radicals CH3, Cl and H are most abundant. CH4, C2H2, and also smaller amounts of C2H4 and C2H6 are in a quasi equilibrium. The chlorinated hydrocarbons were close to the detection limit.