Plasma excitation coil

• Main Authors: Howald, Arthur M, McMillin, Brian, Lin, Frank Yun
• Format: Patent
• Language: English
• Published: 11.11.2003

The present invention relates generally to plasma excitation coils and, more particularly, to an excitation coil having at least one capacitance connected across a discontinuity between the coil excitation terminals, and to a workpiece processor including such a coil. The invention also relates to a method of operating an excitation coil such that a standing wave has a sudden amplitude and slope change, as well as a sudden slope reversal, between the coil excitation terminals. A spiral-like multi-turn coil excites a plasma for treating a workpiece in a vacuum plasma processor. In one embodiment two of the turns have a discontinuity. Each discontinuity has a capacitor connected across it. An RF source drives the coil via a matching network, an inductor connected to one coil excitation terminal and a capacitor connected to another coil excitation terminal. The impedances of the inductors and the capacitors at the RF source frequency and the discontinuity locations are such as to cause a standing wave voltage of the coil to have (1) equal and opposite values at the coil terminals, (2) sudden amplitude and slope changes, slope reversals and polarity reversals at each of the discontinuities, and (3) three gradual standing wave voltage polarity reversals, spaced from each other by 120°. Two of the gradual polarity reversals are azimuthally aligned with the discontinuities. In a second embodiment, one turn has a discontinuity having a series capacitor connected across it. A shunt capacitor is connected between the discontinuity and ground.