Diagnostics of an inductively coupled CF4/Ar plasma

Abstract

Experimental data for radiative and metastable state densities in pure argon and in mixture of 5% CF4 in argon are obtained to study the effect of CF4 on kinetics of inductively coupled plasma (ICP). The measurements were made by a combination of optical emission spectroscopy and computer tomography for radiative levels and by laser absorption for metastable state profiles. The data were obtained in an inductively coupled rf (13.56 MHz) plasma with a single coil and full cylindrical symmetry. At low pressures of 5 and 15 mTorr the data in pure argon and in the mixture do not differ much, both in the magnitude and in the radial and axial profiles. However, at 50, 100, and 300 mTorr there is a dramatic change when CF4 is introduced. The metastable density increases due to the smaller electron induced quenching while axial and radial profiles are quite different. Unfortunately introduction of CF4 spoils the degree of azimuthal isotropy. The observed results and explanations based on the important role of metastables and stepwise processes in kinetics of high electron density ICP are supported by measurements of plasma density by using a double probe.