Distributed ECR: Concept, Performances and Perspectives

Abstract

Multipolar magnetic field confinement was suggested 25 years ago by Sadowskil as a means of providing high density plasmas. Since the experiments of Limpaecher and MacKenzie2 on discharges confined by multipolar magnetic fields, many other devices also using multipolar field configurations have been constructed. Compared with the same chamber used whithout magnetic field, and for a given discharge power level, the multipolar magnetic field confinement was shown to increase plasma density by as much as two orders of magnitude and also to improve plasma homogeneity.2 Considering plasma processing at the industrial level where large areas of dense and uniform plasmas are most often required, such a confinement thus appears well adapted for improving plasma performances. But, the use of filaments or hot cathode discharges in sustaining plasmas of reactive gases in multipolar confinement structures3 was progressively ruled out in favor of RF4–6 or microwave plasma sources.7–9 Surface wave7,8 and electron cyclotron resonance (ECR) microwave sustained discharges9 were investigated as plasma sources external to the multipolar magnetic structure. But, in such devices, plasma density is limited by the ratio of the surface area of the source to the volume of the reactor into which plasma diffuses. Solving this problem was the primary goal pursued in developing a new ractor concept based on multipolar magnetic confinement, and termed distributed ECR (DECR) discharges10. This new design allows to integrate the microwave field applicator ensuring plasma excitation to the multipolar magnetic confinement structure where ECR conditions are met. Such a system allows to adjust the plasma generation as a fonction of the required reactor size.