Plasma production in large volume plasma system by compact electron cyclotron resonance sources

Abstract

Summary form is given. There are several applications which require plasma to be produced over large volumes (~ few cubic meters) and where it is desirable to have high radial / axial uniformity and high plasma density. Although electron cyclotron resonance (ECR) plasma sources are efficient and yield high plasma densities1 these do not scale well with the volume. This paper presents a scheme for large volume plasma production that retains the advantages of ECR plasma sources without sacrificing on uniformity or high plasma density. It uses multiple, compact ECR plasma (CEP) sources2 that are highly portable and easily mountable on any chamber. The large volume plasma system (LVPS) described in the paper is a scalable, circular cylindrical vessel of diameter = 1m, consisting of source sections (SS) and spacer sections (SPS). The CEPs are mounted in an azimuthally symmetric manner on matching ports along the periphery of the source sections, and the system was configured for 4 / 6 CEPs (one SS, two SPS, height = 1.1 m) and 8 /12 CEPs (two SS and three SPS, height = 1.55 m). Since plasma filling of the system in this scheme is radially inwards, the decrease in the volume to be filled as the plasma flows inwards, partially offsets the depletion of plasma as it flows away from the sources. This results in a more uniform plasma density over the system volume. The scheme also takes advantage of the magnetic field of the CEPs (produced by ring magnets) to produce a cusp magnetic field inside the chamber aiding confinement and uniformity. Typically, the bulk plasma density in the LVPS is = 5x1010 cm-3 to = 5x1011 cm-3 and bulk electron temperature = 1 - 2 eV, depending on argon gas pressure (0.5 - 10 mTorr) and microwave power (200 - 600 W per CEP at 2.45 GHz). The radial uniformity is typically = 2 to 5 % up to r = 0.4 m. The paper presents detailed results in conjunction with the theoretical model developed.