Acetylene–argon plasmas measured at a biased substrate electrode for diamond-like carbon deposition: I. Mass spectrometry

We report, for the first time, quadrupole mass spectrometry of neutral and positive ionichydrocarbon species measured at the rf-biased substrate electrode of an inductively coupledplasma for acetylene rich C2H2 :Ar mixtures under various bias, frequency and pressureconditions. It has been observed that, irrespective of initial gas mixture, the resultant plasma isdominated by argon neutrals and ions. This is attributed to highly efficient conversion ofacetylene to C2H due to the enhanced electron density compared with a standard capacitiveplasma where the acetylene (neutral and ion) species remain dominant. This conversion maybe crucial to film formation via inert rather than hydrocarbon ion bombardment. In addition,the transient formation of CH4 from acetylene has been discovered using IR absorptionspectroscopy with time constants similar to observed pressure variations. Rate coefficients andrates for many of the reaction mechanisms, calculated using measured electron energydistribution functions and species densities, are given. These results have importantapplication in plasma models and growth studies for hydrogenated amorphous or diamond-likecarbon film deposition. Film growth under similar plasma conditions is reported in