Plasma showerhead assembly and method of reducing defects

A plasma showerhead assembly comprising:

• a conductive plate including a plurality of gas channels and a plurality of conductive plate gas openings;
• a dielectric faceplate comprising a plurality of dielectric resonators and a plurality of dielectric faceplate gas openings in fluid communication with the plurality of the conductive plate gas openings, the dielectric faceplate configured to be assembled to the conductive plate;
• a plurality of o-rings surrounding the plurality of conductive plate gas openings and the plurality of dielectric faceplate gas openings and configured to seal the plurality of dielectric faceplate gas openings and the plurality of conductive plate gas openings from atmospheric pressure;
• and
• a conductive insert disposed within at least one of the plurality of dielectric faceplate gas openings, the conductive insert having a length with an aperture extending through the length of the conductive insert, the aperture having an inner diameter.