ECR Plasma Sources

Abstract

Microwave-produced low-density plasmas are being successfully used for various technical surface processes, like thin-film deposition, various surface treatments, or microstructuring by reactive ion etching (see, e.g. [4, 18, 1]). In this specific area of plasma processing, the use of the electron-cyclotron resonance (ECR), achieved by superimposing a weak magnetic field to the configuration, led to substantial improvements. The resulting ECR sources offer several advantages, the most important ones being:Plasma processing can be carried out without electrode or vessel interactions as potential sources of impurities.The resonant power absorption allows operation in an extremely wide range of gas presssures or particle densities.The degree of ionization and hence the plasma density can achieve values much above those of low-frequency RF- or DC discharges.The high electron density increases with power and the tail possesses almost thermal energy distribution function as predicted by kinetic calculations [8, 10, 5] and recently confirmed experimentally in a microwave discharge [9].Both features seem responsible for the high production rates of reactive particles (molecular fractals and radicals like atomic hydrogen, oxygen, CHxetc. or molecular ions) which are characteristic for microwave- and specifically ECR discharges and which are responsible for the high deposition or etching rates in these devices.The high frequency operation with ω ≫ ωpi= ion plasma frequency is able to avoid the formation of large RF sheath potentials as well as the resulting surface bombardment, and eventually destruction, by the energetic ions [21].