Radio-frequency magnetized ring-shaped hollow cathode discharge plasma for low-pressure plasma processing

Influence of magnetic field configuration on ring-shaped hollow cathode discharge has been investigated in order to perform high-density plasma sources under a low gas pressure of a few tens mTorr. Three typed arrangements of permanent magnets such as (a) NS-NS, (b) NS-SN and (c) NS are examined. The NS-NS arrangement has a divergent profile with a peak in axial direction in hollow cathode. The NS-SN placement forms a cusp profile with a mirror configuration in axial direction. In final, the NS setup assigns a conventional divergent field. For the cases of (a) NS-NS and (b) NS-SN arrangements, their plasma density keeps a higher order of magnitude of 1011 cm−3 at the wide range of gas pressure of 10-200 mTorr. On the other hand, the NS arrangement maintains only the order of magnitude of 1011 cm−3 at the region of gas pressure more than 30 mTorr. All radial profiles of plasma density near the hollow cathode show non-uniformity like M-shaped distribution. However, it is found that the uniformity of their radial profiles depends on the arrangement of permanent magnets.