Patent ID: 7829469

Claim:
A method of etching a thin film on a substrate using a plasma processing system, comprising: disposing said substrate on a substrate holder in said plasma processing system; coupling direct current (DC) power at a first DC voltage to an electron source electrode opposing said substrate on said substrate holder within said plasma processing system in order to create a ballistic electron beam; coupling alternating current (AC) power to said plasma processing system in order to form a processing plasma in said plasma processing system; coupling DC power at a second DC voltage to a ring electrode located beyond a peripheral edge of said substrate and opposite said electron source electrode in order to increase the plasma density of said processing plasma near said peripheral edge of said substrate; coupling DC power at a third DC voltage to an auxiliary electrode located beyond a peripheral edge of said ring electrode; and adjusting the amount of surface area on said auxiliary electrode that is exposed to said processing plasma in order to further alter the amount of increase to the plasma density near the peripheral edge of said substrate.