Electromagnetic fields in a low-pressure planar inductively coupled plasma source

Abstract

Summary form only given. The results of experimental and theoretical studies of electromagnetic fields in a planar radio-frequency (13.56 MHz) inductively-coupled plasma (ICP) source will be compared. Experimental measurements have been performed using inductive loop probes oriented to measure the time derivatives of the axial and radial components of the magnetic field (B/sub z/ and B/sub r/, respectively). The measurements of B/sub z/ were used to calculate the asimuthal component of the inductive electric field E/sub /spl phi// directly from Faraday's law, taking advantage of cylindrical symmetry. Using B/sub z/ rather than B/sub r/, allows calculation of E/sub /spl phi// without any approximations or knowledge of plasma parameters, and as such should give a more accurate estimate of E/sub /spl phi//. In order to investigate the degree of electromagnetic field shielding by the plasma, measurements were taken with argon plasma, in the range of operating pressures between 5 and 50 mTorr and rf power between 50 and 500 Watt, as well as without the plasma. It was found that an essential shielding of the E/sub /spl phi// field by the plasma is observed near the discharge axis while the field profile near the chamber walls is governed by a geometrical effect rather than by plasma shielding. Lower gas pressure and lower rf power (lower plasma density) corresponded to less effective shielding of the fields. Simultaneous measurements of B/sub r/ and B/sub r/ allowed estimation of the local permittivity of the plasma /spl epsiv/ according to /spl nabla//spl times/B=/spl mu//sub 0//spl epsi/E. A plasma density profile calculation compares favorably with Laugmuir probe measurements.