The effects on plasma properties of a current node on inductively coupled plasma sources

We report our measurements of inductively coupled plasmas produced by sources having a current node (current reversal) along their length. It was found that a current node neither prevented the production of high-density plasma for the tested source designs nor completely destroyed the plasma uniformity. In addition, carefully designed source geometries could tailor the effects of a current node along the source length and open the possibility for very large area sources with very good uniformity. As one example, the azimuthal electric field symmetry as well as ion and electron density uniformity can be improved by simply reversing the direction of travel for loops following the current node. We also measured the electron temperature profiles using a Langmuir probe, and found that they agree qualitatively with the measured electric field profiles for our source designs. In fact, the plasma produced by a conventional source design exhibited a significantly lower electron temperature than that by a very similar, reversed-loop, source design even while the electron density was nearly equal. We speculate that the lower electron temperature is due to a reversal in the azimuthal electric field for the conventional source design.