INVESTIGATIONS CONCERNING THE ROLE OF HYDROGEN IN THE DEPOSITION OF DIAMOND FILMS

The usual process gases for the chemical vapour deposition of diamond films with hot-filament or microwave techniques contain only a few per cent of a hydrocarbon diluted in hydrogen, because it is often stated that a superequilibrium concentration of atomic hydrogen is required. We performed deposition experiments on Si(111) substrates in a microw ave plasma without hydrogen dilution. By using Ar-CH4-O2 and Ar-C2H2-O 2 mixtures, the hydrogen content in the plasma was reduced. Diamond gr owth took place only in a definite range of gas compositions. Our expe riments show that oxygen is partly able to play the role of hydrogen b y suppressing the deposition of amorphous or graphitic phases. The pha se purity of the diamond films was investigated with Raman spectroscop y and scanning electron microscopy. In order to monitor the plasma che mistry and its changes due to oxygen addition and the reduction of the hydrogen concentration, the plasma gas composition was measured with a differentially pumped quadrupole mass spectrometer. The measurements show that oxygen effectively lowers the content of acetylene in the p lasma. Our investigations suggest that acetylene is not the main growt h species.