Functional coating deposition using plasma is broadly used in industrial application working at a pressure ranging from low pressure discharges (a few Pascals) to atmospheric plasmas. The active gas (silane is selected for this study) is often diluted in a gas that helps in stabilizing the discharge like helium or argon. In addition, the discharge can be polluted by uncontrolled external gas source like air or oxygen coming from water adsorbed in reactor walls. In this paper, we study the interactions taking place within the bulk of a capacitively coupled plasma and study the impact of these reactions on the flux of species moving towards the substrate and so the impact on the composition of deposited film. A one-dimensional fluid model is presented for the modelling of radio frequency capacitively coupled plasmas in a mixture of silane/helium, including small concentrations of O2 and N2. In total, 48 different species (electrons, ions, neutrals, radicals and excited species) are considered in the model. After a sensitivity study, 27 electron–neutral and 76 chemical reactions (i.e. ion–neutral and neutral–neutral reactions) were maintained in the fluid model. The fluid model itself consists of a set of mass balance equations (i.e. one for every species), the electron energy equation and the Poisson equation. The reaction rate coefficients of the electron–neutral reactions, as a function of average electron energy, are obtained from a Boltzmann model. The reaction rate coefficients of the ion–neutral and neutral–neutral reactions are assumed to be constant. It is found that helium does not affect the silane plasma chemistry drastically. The incorporation of small amounts of air (containing about 82% N2 and 18% O2) in a silane/helium plasma, however, influences the plasma chemistry to a large extent. A large number of nitrogen species (i.e. N2, N, N2+), and species containing oxygen (i.e. SiH3O SiO, OH and others), are present in the discharge at relatively high densities (i.e. of the order of 1014–1017 m−3).

Four new low field side antennae grouped in pairs have been installed on TEXTOR. It is found that the interaction with the wall (density rise, impurity generation) is significantly reduced when operating each pair out of phase (E) as opposed to in phase (0). The beneficial effect in the n configuration is obtained without drop in plasma loading. This experimental property is shown, from theory, to be explained by the judicious choice of the geometrical configuration. A further improvement in the wall interaction is made possible by an appropriate choice of wall conditioning (wall carbonization with liner at 400'C or. above all, boronization). As a result record low values of PYsd/Ptota, were achieved during ICRH. The large reduction in wall interaction during ICRH allows routine long pulse (> 1 s) ICRH operation at the maximum power level available (g 2.5 MW).

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Thc cxcilalion of Past-wave global cigenmodcs is investigatcd but11 experimentally for TEXTOR and theoretically using a slab coupling mode. A briefcomparison with a cylindrical model shows that in the TEXTOR situation no essential gcometricdl cflcct is left out by thc slab code. Thc resonant behaviour associatcd with eigcnmodcs is studied fctr several signals: the resistancc and inductance of the antennae, the r.f. magnetic and clectric field components picked up by probes at thc plasma edge, and thc power coupled to a Pdst-wave antcnnil uscd its a receiver It is shown that all thc major features of thesc signals linked to thc existencc of cige"ies can be cnplaincd using the theoretical models. Two possibly counterintuitive conclusions of this study are (aJ that the absence of iesonance peaks in thc rrsislmcc curves o f the rr-phased antennae docs not imply that the cigcnmodes itre not excited a1 similiir lcvcls its for the 0-phasing. and (h) that the variations in local r.f. field magnitude arc ziot closely related l o the rcsanant bchaviuur ofthc antenna resistancc. I . I N T R O D U C T I O N * R ;ind L iiic thc rcsist:mx and inductance per unit length of the antenna. coiisidercd ils il strip line; B prccisc dclinition is givcn by M E S S ~A ~X e, 01. (IOSZ).

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