Investigations concerning the role of hydrogen in the deposition of diamond films

Abstract

Abstract 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 microwave plasma without hydrogen dilution. By using Ar-CH4-O2 and Ar-C2H2-O2 mixtures, the hydrogen content in the plasma was reduced. Diamond growth took place only in a definite range of gas compositions. Our experiments show that oxygen is partly able to play the role of hydrogen by suppressing the deposition of amorphous or graphitic phases. The phase purity of the diamond films was investigated with Raman spectroscopy and scanning electron microscopy. In order to monitor the plasma chemistry 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 plasma. Our investigations suggest that acetylene is not the main growth species.