8 - Distributed ECR Plasma Sources

Abstract

This chapter discusses mechanisms of multipolar magnetic field confinement and the principle of distributed electron cyclotron resonance (DECR) plasma systems. The chapter begins with the history of multipolar magnetic field confinement, with a short description of the confinement structures currently used and of the properties and characteristics of confined plasmas. It is mentioned that main advantage of plasma processing over many other dry processing techniques lies in the generation of ions and active neutral species (reactive atoms, radicals) that allow processing at ambient or even cryogenic temperatures. Distribution of plasma sources is an attractive concept providing plasma homogeneity in atomic gas plasmas. This has been achieved in cylindrical distributed electron cyclotron resonance and uniform distributed electron cyclotron resonance (UDECR) plasmas by combining electron cyclotron resonance (ECR) excitation with a multipolar magnetic field.Ion volume recombination, responsible for the lack of homogeneity in molecular gas plasmas, imposes limitations on the uniformity of plasma processing. In the case of large plane substrates, this problem can be avoided by adopting a plane configuration for the plasma source. Large plane UDECR plasmas can be obtained by associating parallel linear applicators in a planar configuration. The possibility of producing such uniform plasmas has been proven experimentally. In contrast with capacitive discharges, substrate surfaces can be biased independently of plasma generation allowing control of the ion bombardment energy. Because of the UDECR, the possibility of scaling processes from a small to a large reactor exists without any alteration in the characteristics. The concept of uniform distribution for plasma sources must be extended to gas feeding, pumping, substrate biasing, and also substrate heating or cooling, if uniform processing is desired.