Characterization of hydrogen microwave plasmas produced by elementary sources in matrix configuration

International audienceIn a previous study, a planar plasma reactor comprising 4 × 3 elementary microwave plasma sources distributed according to a square lattice matrix configuration was first characterized with argon. In this work, the objective is to characterize these so-called matrix plasmas with hydrogen in view of surface processing applications. In the absence of a static magnetic field, hydrogen plasmas can be sustained uniformly in the medium pressure range from 10 to 70 Pa. Using a cylindrical Langmuir probe, plasma density and electron temperature have been investigated at a distance of 20mm from the source plane as functions of pressure and microwave power. The results show that the electron temperature Te is of the order of 1.2 eV and that plasma densities up to a few 1011 cm−3 can be reached. Under the same experimental conditions, optical emission spectroscopy measurements have been performed in order to determine the gas temperature and the degree of dissociation of hydrogen. The gas temperature, calculated from the α–Fulcher Q branch emission band (2–2) d 3П−u a 3Σg, varies from 600 to 850K ± 50 K. The degree of dissociation has also been determined by using a spectroscopic method based on emission line intensities of Hα, Hβ and H2 (2–2) d 3 П −u a 3Σg (N = 1) species. The maximum degree of dissociation of 50% has been obtained for the operating conditions corresponding to the highest plasma density