AVS 47th International Symposium
    Plasma Science and Technology Tuesday Sessions
       Session PS-TuP

Paper PS-TuP22
Penetration of Electromagnetic Fields in ICP, Weakly Magnetized ICP, and Low-B Helicon Discharges

Tuesday, October 3, 2000, 5:30 pm, Room Exhibit Hall C & D

Session: Poster Session
Presenter: J.D. Evans, University of California, Los Angeles
Authors: J.D. Evans, University of California, Los Angeles
F.F. Chen, University of California, Los Angeles
D. Arnush, University of California, Los Angeles
Correspondent: Click to Email
Due to renewed interest by the plasma processing community, the physics of the penetration of electric and magnetic fields in low pressure, weakly ionized plasmas is an area of active research. Penetration of induced B-fields in ICP, weakly magnetized ICP, and low-field helicon discharges is investigated in a device consisting of a dome-shaped Pyrex top attached to a magnetic bucket. The antenna consists of a multi-turn loop of wire wrapped around the top (radius = R@sub top@), and B@sub o@ is produced by a magnet coil located near the antenna. B@sub z@-dot probes are used to measure B@sub z@-field profiles. B@sub z@ decays approximately exponentially with decreasing R in most cases. Characteristic decay lengths of B@sub z@ (L@sub sd@) are measured as P@sub o@ is varied. Good agreement between experiment and collisional skin depth theory is observed for f@sub RF@ = 2MHz when non-uniform density profiles are taken into account. Experimental values greatly exceed collisional theoretical predictions for f@sub RF@=6.78MHz, in qualitative agreement with anomalous skin effect (ASE) theory. Variations of L@sub sd@ with B@sub o@ have also been measured, and good agreement between experiment and collisional theory is observed in most cases. Regions of enhanced B@sub z@ ("wings") are observed near the edge for B@sub o@>0, in qualitative agreement with code predictions when axial boundary conditions are accounted for. As B@sub o@ increases, L@sub sd@ increases, and B@sub z@ in the interior increases. Coupling to a low-B@sub o@ helicon mode is expected when L@sub sd@ @>=@ R@sub top@. Under these conditions, the B@sub z@-field amplitude behavior changes from evanescence to propagation. At higher powers and neutral pressures, large phase shifts in B@sub z@, apparent "nodes" in B@sub z@ amplitude profiles, and other interference-type phenomena are observed, even in highly collisional regimes where ASE is not predicted to occur.