Ion Acceleration in ICP Source

Summary form only given. For charging damage free etching it is necessary to bombard the substrate with energetic ions. A new ICP device was constructed for ion acceleration in the plasma without using electrodes. Plasma is produced between two coaxial quartz cylinders with a flat coil placed on the top. Interaction between RF magnetic field and induced plasma current produces ponderomotive force accelerating electrons downstream the channel into the cylindrical main vacuum chamber. Plasma parameters are measured by double and single Langmuir probes, while for ion energy measurements a movable retarding field energy analyzer is used. Measurements show that at low pressures (about 1 mtorr) and high input powers (more than 800 W), the plasma potential decreases rapidly in the boundary zone between discharge channel and main chamber. This potential drop leads to ion acceleration into the chamber. Measurements of ion energy distribution in the chamber near the channel exit show the existence of hot ions with kinetic energies up to 15 eV. Such ion energy is consistent with the plasma potential drop at the channel exit. Similar results with hot ions formation in the region of diverging magnetic field were obtained in helicon plasma sources. Our investigations show that pronounced ion acceleration can be demonstrated in an ICP-type plasma source without static magnetic field