Large microwave plasma reactor based on surface waves

A microwave plasma reactor without magnetic fields has been designed for la rge surface treatment or deposition. Using the surfaguide principle, a 2.45 GHz wave is coupled to the plasma created in a 12cm tube diameter surrounde d by a metallic cylinder of 18.8cm diameter. The aim of this paper is to ch aracterize this plasma, particularly the spatial homogeneity over the cross section. Argon and oxygen gases have been used. Pressure and microwave pow er were in the range 1 to 1000 Pascal and 200 to 2000Watt. Wave propagation study has shown that mainly a plasma mode (surface wave) of azimuthal hexa polar symmetry (pi/3 periodicity) propagates. In argon gas, electron densit y (10(11) to 10(12) cm(-3)) and mean energy (1 to 3 eV) are locally measure d by probes. Emission spectroscopy provides information on excited states d istributions. They depend an the electric field distribution : azimuthally pi/3 periodic and radially maximum near the wall due to the surface wave pr ofile. Weakly modulated at high pressure, they are quite homogeneous at low er pressure due to the diffusion phenomenon. Actinometry has shown that the atomic oxygen density is rather homogeneous over the cross section whateve r the pressure, which is promising for future surface treatment application s.