Showerhead with air-gapped plenums and overhead isolation gas distributor

A method comprising:

• flowing one or more process gases out of a first gas distributor, the first gas distributor including:
• a plurality of plenum structures and multiple sets of gas distribution ports, each set of gas distribution ports connected with a corresponding plenum structure and each plenum structure including a corresponding plenum volume, wherein:
• the multiple sets of gas distribution ports include a first set of first gas distribution ports and a second set of second gas distribution ports,
• the plurality of plenum structures includes a first plenum structure including a first plenum volume and a second plenum structure including a second plenum volume,
• the first gas distribution ports are connected with the first plenum structure and configured to direct gas flowed through the first gas distribution ports from the first plenum volume along a first average direction,
• the second gas distribution ports are connected with the second plenum structure and configured to direct gas flowed through the second gas distribution ports from the second plenum volume along the first average direction, and
• the first plenum structure and the second plenum structure are separated from each other by at least a first gap when viewed along the first average direction;
• and
• flowing an isolation gas out of a second gas distributor while process gas is flowed out of the first gas distributor, the second gas distributor including an isolation gas plenum volume and a plurality of isolation gas ports in fluidic communication with the isolation gas plenum volume, wherein:
• the second gas distributor is positioned such that the isolation gas ports are interposed between the isolation gas plenum volume and the first gas distributor, and
• the isolation gas ports are configured to flow gas flowed through the isolation gas ports from the isolation gas plenum volume towards the first gas distributor and through the first gap.