Optical Emission Diagnostic of a Low Pressure Planar Microwave Discharge for Plasmachemical Deposition

Low pressure microwave plasmas are of growing interest for plasmachemical applications since they have special and in some cases unique advantages with respect to other plasma excitation methods. Subject of this paper are spatially resolved measurements of the optical emission of a special planar microwave plasma source utilized to investigate different plasmachemical processes. The optical emission spectroscopy (OES) is used as a tool to get information concerning the spatially distribution of reactive atom and molecule concentration by actinometry and concerning the neutral gas temperature by measurements of Doppler line broadening. The results refer to hydrocarbon containing hydrogen plasmas which gas pressures above 100 Pa. Surprisingly measurements confirm an earlier developed simplified two layer model consisting of a preferentially physically active plasma layer near the microwave window followed by a preferentially chemically active decaying region. They give evidence that this model is more adequate to the real physical situation as assumed until now.