Patent ID: 8623171

Claim:
A plasma processing apparatus comprising: a process chamber; a platen positioned in the process chamber for supporting a workpiece; a source configured to generate a plasma in the process chamber having a plasma sheath adjacent to the front surface of the workpiece; an insulating modifier configured to control a shape of a boundary between the plasma and the plasma sheath so a portion of the shape of the boundary is not parallel. to a plane defined by a front surface of the workpiece facing the plasma, the insulating modifier comprising a pair of insulators defining a gap there between; a bias source configured to bias the wafer relative to the process chamber to attract ions from the plasma across the plasma sheath towards the workpiece, and a controller configured to control the source, the gap, and a vertical spacing between the pair of insulators and the plane, to define the shape of the boundary about the gap to be a convex shape bulging outward away from the plane when the ions are accelerated across the plasma sheath towards the workpiece.