Speaker
Jay Kirtikumar Joshi
Description
See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.4008.pdf
Impedance characteristics of a magnetized 13.56 MHz capacitive discharge
J.K. Joshi, S.K. Karkari and Sunil Kumar
Institute for Plasma Research, HBNI, Bhat, Gandhinagar, India
*e-mail: jay.joshi@ipr.res.in
Capacitive driven discharges are well known due to its vast application in microelectronics
industries. The operating RF frequency, ωrf, typically lies between electron and ion plasma
frequencies, such that ωpe >> ωrf > ωion. The overall impedance of the discharge remains
largely capacitive due to the sheath reactance; while the bulk plasma remains inductive. The
plasma condition at which the reactance of the sheath and the bulk plasma mutually cancels
out is identified as the electron series resonance (ESR).
In this work the existence of ESR in the presence of transverse magnetic field, has been
investigated from the impedance characteristics of the discharge, for a planar plate and
cylindrical electrode configuration in a linear device. The impedance characteristics have
been obtained from phase calibrated external power measurements.
It is found that the net reactance in the case of parallel plates changes from inductive to
capacitive (positive to negative) crossing zero (ESR) as the plasma density increases with
applied RF power levels. However in the cylindrical configuration, discharge produced in
argon remains largely inductive for the unmagnetized case; whereas it changes to capacitive
in presence of axial magnetic field. For lighter gas helium, the discharge behavior remains
entirely inductive with/without axial magnetic field. This observation can be attributed to
effect of low frequency (ωrf ≈ ωion) RF sheaths, which results in minimal sheath widths
leading to small sheath reactance. The ESR condition for the planar geometry has been
qualitatively explained based on cross-field plasma conductivity model.
