Plasma and electrical characteristics of inductive discharge in magnetic field

Abstract

Summary form only given. The electron energy distribution function (EEDF) and corresponding plasma parameters have been measured in a cylindrical inductively coupled plasma (ICP) immersed in a weak magnetic field and driven at 29 MHz. Concurrently, the azimuthal rf electric field and its phase were measured along the electromagnetic field propagation using a loop magnetic probe. The measurements were performed under condition of controlled rf power delivered to the plasma electrons taking account for the power loss in the induction coil. Under experimental condition the argon pressure varied between 1 and 10 mTorr, the discharge power between 25 and 200 W and magnetic field was up to 20 G. At higher magnetic field the discharge became unstable making Langmuir and magnetic probe measurements impossible. Throughout the experiment /spl nu//spl Lt//spl omega//spl les/2/spl omega//sub c/ and the nonlocality parameter /spl Lambda/=(v/sub th///spl omega//spl delta/)/sup 2//spl Lt/1, where /spl nu/, /spl omega/ and /spl omega//sub c/ are the electron collision, the driving and the cyclotron frequencies, v/sub th/ is the electron thermal velocity and /spl delta/ is the skin depth width. It has been found that considerable modification of plasma parameters at ECR condition occurs only at relatively small discharge power. At large discharge power and thus, at large plasma density, when electron-electron collisions bring the electron energy distribution to equilibrium, the effect of magnetic field on electron temperature and plasma density is relatively small. We showed that at high discharge power, an enhancement in the plasma density with application of magnetic field found in earlier experiments is mainly due to a rise in the power transfer efficiency caused by the reduction in the ICP maintaining rf electric field. Falling of the rf field with increasing magnetic field, suppression of ECR effect and the wave phase velocity close to thermal one found in this work, suggest an onset of wave propagation and absorption at magnetic fields much weaker than that in typical helicon plasma sources.