Vacuum plasma processor having coil with added conducting segments to

Abstract

A vacuum plasma processor for treating a workpiece with an RF plasma has a plasma excitation coil including a peripheral portion supplying a substantial magnetic flux density to peripheral portions of the plasma. Additional conducting segments spatially adjacent to and electrically connected to a segment of the peripheral portion supply additional magnetic flux having a substantial magnetic flux density to the plasma peripheral portions. The additional conductor segments are in each of four corners of the coil, being connected electrically in parallel or series to coil conductor segments forming the corners. In another embodiment, the coil includes several nested conducting corner segments. In different embodiments, the corner segments are (1) coplanar with the remainder of the coil and (2) closer to the plasma than the remainder of the coil. The coil includes two electrically parallel, spiral like windings, each with an interior terminal connected to one output terminal of a matching network and an output terminal connected via a capacitor to another output terminal of the matching network. The capacitor values and the lengths of the windings relative to the plasma RF excitation wavelength are such that current flowing in the coil has maximum and minimum standing wave values in the peripheral and interior coil portions, respectively. The coil and workpiece peripheries have similar rectangular dimensions and geometries.