Helicon waves in theory and experiment

Summary form only given, as follows. The use of helicon waves to produce high density plasmas for semiconductor chip fabrication tools is by now well known in that industry. Basic research on helicon discharges in the last ten years has greatly improved our understanding of how these plasma sources work. At high magnetic fields, the wave fields have been carefully measured and found to agree well with the classical theory of helicon waves. The theory has been extended to low magnetic fields by including the coupling to cyclotron waves. Experiments in this range have also been done. The transition to zero magnetic field turns out to be nontrivial and rather interesting; this is a region in which many industrial plasma sources operate. As a result of efforts by several groups, numerical computations that include the effects of damping, plasma inhomogeneity and antenna coupling can now be made on a simple computer. Unfortunately, the very nonuniform magnetic fields in production tools still require extensive modeling. We are now in a position to answer several intriguing questions that have puzzled experimentalists for many years: 1) What is the rf absorption mechanism that makes helicon discharges so efficient? 2) Why is the m=-1 azimuthal mode so much harder to excite than the m=+1 mode? 3) What causes the discontinuous jumps in density as the magnetic field or rf power is increased? 4) What fields are generated under and near the antenna? Experimental and theoretical data that bear on these questions will be shown.