Mass spectrometric studies of a CH4/H2 microwave plasma under diamond deposition conditions

We report on mass spectroscopic measurements of species originating from a microwave (MW) discharge plasma under simulated diamond deposition conditions. The plasma is produced in a 30 W MW flow tube through which flows a gas mixture of about 1% methane admixed in hydrogen. Plasma composition was investigated as a function of gas component ratio by Li+-ion attachment mass spectrometry. C, C2, C2H, C2H2, and C2H4, together with the free-radical species of C2H3 and C2H5, were observed on the mass spectra as Li+-ion adducts. Atomic carbon was the most abundant species, suggesting an important role for atomic carbons in diamond film growth.