Methods and apparatus for symmetrical hollow cathode electrode and discharge mode for remote plasma processes

An apparatus for processing a substrate, comprising:

• a remote plasma source (RPS) having a first plasma source with a first electrode and a second electrode, wherein the first electrode and the second electrode are formed of or coated with a nickel-based material and are symmetrical with hollow cavities having opposing cone shapes with a largest opening of each of the hollow cavities opposing each other, wherein the first electrode and the second electrode are configured to induce a hollow cathode effect within the hollow cavities,
• wherein the first electrode and the second electrode have parallel surfaces opposing each other that surround the largest opening of each of the hollow cavities and are separated by a gap, and wherein the first electrode and the second electrode are at least partially coated with a ceramic material that is configured to reduce sputtering between the parallel surfaces during generation of plasma in the RPS;
• a radio frequency (RF) power source configured to provide a symmetrical driving waveform on the first electrode and the second electrode to produce an anodic cycle and a cathodic cycle of the RPS, wherein the anodic cycle and the cathodic cycle operate in a hollow cathode effect mode;
• and
• an isolator with a ring shape positioned between the first electrode and the second electrode and configured to reduce electric fields between the first electrode and the second electrode during generation of plasma in the RPS.

A method of generating remote plasma for a process chamber, comprising:

• generating a symmetrical driving waveform with a radio frequency (RF) power source for a first plasma source;
• forming plasma in the first plasma source by applying the symmetrical driving waveform to a first electrode and to a second electrode of the first plasma source, wherein the first electrode and the second electrode are formed of or coated with a nickel-based material and are symmetrical with hollow cavities having opposing cone shapes with a largest opening of each of the hollow cavities opposing each other, wherein the first electrode and the second electrode are configured to induce a hollow cathode effect within the hollow cavities, wherein the first electrode and the second electrode have parallel surfaces opposing each other that surround the largest opening of the hollow cavities and are separated by a gap, and wherein the first electrode and the second electrode are at least partially coated with a ceramic material that is configured to reduce sputtering between the parallel surfaces during generation of plasma in the first plasma source;
• and
• reducing electric fields between the first electrode and the second electrode during formation of plasma by positioning an isolator with a ring shape between the first electrode and the second electrode.