Plasma showerhead treatment methods

A method of treating a plasma showerhead, the method comprising:

• placing a showerhead comprising a faceplate having a lower surface and a plurality of gas openings in the faceplate in a plasma processing chamber above a substrate support so that there is a space defining a process volume between the substrate support and the faceplate;
• exposing the showerhead comprising the faceplate and the plurality of gas openings to a gas mixture comprising a silicon-containing precursor having a gas concentration and a reactant gas containing one or more of oxygen and nitrogen so that the process volume and the gas openings are filled with the silicon-containing precursor and the reactant gas;
• flowing a concentration-reducing purge gas for a first period of time to reduce the gas concentration of the silicon-containing precursor in the gas openings;
• introducing a first microwave plasma in the plasma processing chamber for a time sufficient to form a silicon oxide thin film on the lower surface of the faceplate and lining the gas openings;
• flowing a precursor-removing purge gas for a second period of time longer than the first period of time to remove any remaining silicon-containing precursor from the process volume and the gas openings;
• and
• introducing a second plasma in the plasma processing chamber to densify the thin film on the lower surface of the faceplate and lining the gas openings.