STUDY OF THE PLASMA DISCHARGES IN DIAMOND DEPOSITION WITH DIFFERENT O2 CONCENTRATIONS

The effect of the O2 concentration in the structure of diamond films d eposited from CH4-H-2-O2 gas mixtures by microwave chemical vapor depo sition has been studied. For oxygen-to-methane ratios in the 0-0.75 ra nge a strong increase in the diamond content in the films has been obs erved. At higher oxygen-to-methane ratios the diamond content in the f ilm stabilizes and then decreases, resulting in no carbon deposition w hen the oxygen concentration exceeds the methane concentration in the discharge. The emission intensity corresponding to carbon-hydrogen spe cies (CH + and CH), detected by optical emission spectroscopy slightly decreases with the oxygen concentration in the plasma. Only an increa se in the 300-312 nm emission range has been measured, which can be re lated to the presence of activated CO and OH species in the discharge, in agreement with the results obtained by mass spectrometry. We have related the diamond content in the films with the CO mole fraction pre sent in the discharge.