Plasma showerhead assembly and method of reducing defects

A plasma showerhead assembly comprising:

• a conductive plate including a first surface and a second surface opposite to the first surface defining a conductive plate thickness, a plurality of resonator openings extending through the conductive plate thickness, a plurality of gas channels formed inside the conductive plate, and a plurality of conductive plate gas openings extending from the second surface of the conductive plate in fluid communication with the plurality gas channels;
• a dielectric faceplate comprising a first surface and a second surface opposite to the first surface defining a dielectric faceplate thickness, a plurality of dielectric resonators protruding from the first surface and arranged in a pattern and configured to mount through the plurality of resonator openings when assembled, each of the plurality of dielectric resonators having geometric center and an opening to receiving a microwave antenna;
• a plurality of dielectric faceplate gas openings extending through the dielectric faceplate thickness in fluid communication with the plurality of the conductive plate gas openings;
• and
• a plurality of tri-lobed o-rings surrounding the conductive plate gas openings and the dielectric faceplate gas openings and configured to form a seal between the dielectric faceplate gas openings and the conductive plate gas openings from atmospheric pressure.