SPATIAL INVESTIGATION OF A LARGE-DIAMETER MICROWAVE PLASMA

A large diameter plasma (120 mm) is sustained in argon/oxygen mixtures, at low pressure (approximate to 1 Torr) by surface waves at 2.45 GHz. We spatially describe the electromagnetic field distribution as well as the species distribution from diagnostics such as electric antenna probing and emission spectroscopy in the three spatial directions (z, r, phi). According to azimuthal measures (phi), we show that the discharge is mainly maintained by an hexapolar hybrid mode (m = 3). Longitudinal measures (z) exhibit modulations which could be explained by a multimode propagation whereas the radial spectroscopic measures (r) strongly depend on the electric field of the surface wave. However, atomic oxygen densities, nearly 1%, exhibit a quite homogeneous profile in the three spatial directions.