RF Plasma Production at Ultralow Pressures with Surface Magnetic Confinement

Abstract

A 13.56 MHz rf inductively coupled plasma was maintained at pressures as low as 2.7×10 -3 Pa (2×10 -5 Torr) with the use of multidipole magnetic confinement. When more than 90% of the inner wall area was covered with surface magnetic fields, the plasma potential drastically decreased from 80 V to 20 V. These observations were consistent with ambipolar diffusion in partially magnetized plasmas. Additional potential control by an externally biased target was possible over a wide range without changing the plasma density. This large-diameter plasma at very low neutral pressures is promising for new plasma processing techniques.