Gas composition at the substrate in MW-CVD diamond growth: An old problem revisited

Composition of the microwave plasma in chemical vapor deposition (CVD) of diamond in the low pressure range (25 mbar) is reported, using in situ mass spectrometry (MS) in a novel way, to reduce the possibility of recombination for radicals during the sampling process. While the general trends, observed earlier for increasing methane content of the gas feed, are reproduced, it is shown that the relative amount of radicals (most of all CH3 and C2H) is substantially higher than reported before. In fact their total concentration is at least equal to that of the most abundant stable species, C2H2.