Non-ambipolar electric pressure plasma uniformity control

A method for treating a substrate, comprising:

• loading a substrate onto a substrate holder disposed inside a plasma processing chamber, the plasma processing chamber being enclosed by one or more chamber walls and comprising:
• a plasma source configured to energize plasma inside the plasma processing chamber, the plasma processing chamber further comprising:
• a ring-shaped cavity in fluid communication with the plasma processing chamber via a plurality of openings disposed on a wall of the ring-shaped cavity, the ring-shaped cavity comprising an electrode that is configured to be in fluid communication with the plasma, and
• a power supply for biasing the electrode;
• forming a first plasma inside the plasma processing chamber using the plasma source, the plasma having a first plasma density profile;
• and
• forming a second plasma inside the ring-shaped cavity based, at least in part, on, the power supply biasing the electrode, the ring-shaped cavity being in fluid communication with the plasma processing chamber, the second plasma enabling non-ambipolar diffusion of electrons and ions across the plurality of openings.

An apparatus for treating a substrate, comprising:

• a plasma chamber comprising a sidewall and a substrate holder that can support the substrate;
• a gas distribution system that provides gases to the plasma chamber;
• a power supply that can apply power to a plasma source in the plasma chamber, such that a first plasma region can be formed using the gases;
• a diffusion component in fluid communication with the plasma chamber, the diffusion component comprising an electrode that can enable non-ambipolar diffusion in the plasma chamber;
• and
• a power source that can bias the electrode to generate the second plasma region.