Mass and optical emission spectroscopy of plasmas for diamond synthesis

From the compilation of literature data Bachmann et al. demonstrated that the diamond synthesis using different deposition techniques (including excitations by microwave, hot-filament, different kinds of arc plasmas as well as flames) occurs in a small area of the ternary C/H/O diagram with two well defined boundaries of binary mole fractions Xc = C/C+O. This "phase diagram" suggests that the plasma chemistry for a defined C/H/O ratio leads to identical radicals and gas phase species, independly from the different source gases. In order to prove this thesis, we performed a systematic study using different source gases (hydrogen/hydrocarbons/ oxygen) in a microwave deposition system. Informations about the plasma chemistry and its changes due to different gas compositions were gained from mass spectroscopy (MS) and optical emission spectroscopy (OES). The phase purity and the film micro structure of the deposited diamond films were measured using Raman spectroscopy and scanning electron microscopy, respectively. The influence of oxygen addition was determined for two relevant hydrogethydrocarbon (Ch and C2H2) systems. The possibility to deposit diamond without extra addition of H2 is demonstrated for Ar/CH4/02 and Ar/C2H2/02 plasmas.