The scaling up of conventional distributed electron cyclotron resonance plasmas presents limitations in terms of plasma density, limited to the critical density, and of uniformity, due to the difficulty of achieving constant amplitude standing wave patterns along linear microwave applicators in the metre range. The alternative solution presented in this study is the extension of the concept of distribution from one-to two-dimensional networks of elementary plasma sources sustained at electron cyclotron resonance (ECR). With the so-called multi-dipolar plasmas, large size and uniform low-pressure plasmas are produced from a two-dimensional network of elementary, independent plasma sources sustained at ECR. Each elementary plasma source consists of a permanent magnet on which microwaves are applied via an independent coaxial line. The plasma is produced by the electrons accelerated at ECR and trapped in the dipolar magnetic field of the magnet acting as a tri-dimensional magnetron structure. Large-size uniform plasmas can be obtained by assembling as many such elementary plasma sources as necessary, without any physical or technical limitations. Examples of two-dimensional networks are described and the performances in terms of density and uniformity of such plasma sources are presented. The interesting characteristics and advantages of multi-dipolar plasmas over distributed ECR plasmas are listed and the perspectives for plasma processing emphasized.

A parametric study of the etching of polymers has been performed in a 2.45-GHz microwave multipolar plasma using an electron-cyclotron-resonance excitation and an independent 13.56-MHz rf biasing. The etch rates achieved in N2O and N2/O2 discharges are measured as a function of different plasma parameters, i.e., the ion current density bombarding the wafer surface, the ion energy, and the relative atomic oxygen concentration as estimated by actinometry. In both types of plasmas, the etch rate evolutions with ion energy exhibit a two-step variation corresponding first to ion-induced adatom displacements on the polymer surface and second, above a threshold energy, to the rising of sputtering. Under given ion bombardment conditions the polymer etch rate, unchanged by the presence of molecular oxygen, appears to be only controlled by the atomic oxygen concentration in the plasma. The etching kinetics, which first increases proportionally to ion current density and atomic oxygen concentration before reaching saturation, clearly indicates a monolayerlike adsorption of oxygen on polymers. With this hypothesis, the etching behavior can be fully explained by a model recently proposed for plasma etching.