Multizone hollow cathode discharge system with coaxial and azimuthal symmetry and with consistent central trigger

An apparatus for processing semiconductor substrate, comprising:

• a chamber body defining an inner volume;
• a substrate support assembly disposed in the inner volume;
• a hollow cathode plasma source configured to provide one or more processing gas in disassociated phase to the inner volume;
• and
• a showerhead assembly disposed between the hollow cathode plasma source and the substrate support assembly to deliver disassociated processing gas from the hollow cathode plasma source to the inner volume, wherein the showerhead assembly comprises:
• a front plate having a front surface, a back surface and a plurality of first through holes connecting the front surface and the back surface, wherein the front surface of the front plate faces the inner volume;
• a back plate having a front surface, a back surface and a plurality of second through holes connecting the front surface and the back surface, wherein the back surface of the back plate faces the hollow cathode plasma source, and the plurality of first through holes are smaller in diameter than the plurality of second through holes;
• a protective coating is formed on surfaces of the back plate;
• and
• an adhesive layer joining the back surface of the front plate and the front surface of the back plate, wherein the plurality of first through holes are aligned with the plurality of second through holes, and the front plate and the back plate are formed from dissimilar materials.

A method for delivering processing gas in disassociated phase, comprising:

• generating a plasma within a plasma cavity of a hollow cathode plasma source to disassociate a processing gas;
• flowing the disassociated processing gas through a plurality of first through holes in a back plate of a showerhead assembly, wherein a protective coating is formed on surfaces of the back plate;
• and
• flowing the disassociated processing gas through a plurality of second through holes in a front plate of the showerhead assembly, wherein a back surface of the front plate and a front surface of the back plate are joined by an adhesive layer, the plurality of through holes of the back plate are larger in diameter than and are aligned with the plurality of through holes of the front plate, and the front plate and the back plate are formed from dissimilar materials.