Technique for improving uniformity of magnetic fields that rotate or oscillate about an axis

Abstract

Techniques used in systems that employ pairs of coils arranged around an axis to make a magnetic field that rotates around an axis to reduce or eliminate the effects of corners where adjacent ones of the coils meet on the uniformity of the magnetic field. The techniques are particularly useful in plasma reactors that employ magnetically-enhanced reactive ion etching technology. The techniques employ elements that are low cost and may be easily retrofitted to existing plasma reactors. The elements include magnetic shunts that are fitted to the corners of the coils to compensate for the corner effects, trim coils fitted to the corners that, when energized, compensate for the corner effects, and sets of coils that function as 180° coils and thereby reduce the corner effects. The magnetic shunts may be combined with the trim coils. This combination is particularly advantageous for dealing with the two levels of corner effects typically found in a plasma reactor; the magnetic shunt is sized to deal with the lower of the two levels and the shunt together with the energized trim coil deal with the higher of the two levels.

Dependencies are inferred from the claim text.