Plasma processing with preionized and predissociated tuning gases and associated systems and methods

A plasma reactor, comprising:

• a reaction chamber;
• a support element in the chamber for carrying a microelectronic workpiece in a workpiece plane;
• one or more cathode discharge assemblies in the chamber, wherein individual cathode discharge assemblies have a flow port configured to direct a tuning gas upwardly away from the workpiece plane;
• and
• a power supply electrically coupled with the cathode discharge assemblies to control the dissociation and/or ionization of the tuning gas within the flow port.

A plasma processing method, comprising:

• supplying a process gas to a reaction chamber and flowing the process gas in a first direction toward a workpiece;
• forming a plasma zone in the chamber using the process gas;
• flowing a tuning gas through an electric field in a second direction different than the first direction of the process gas, wherein the electric field at least partially dissociates and/or ionizes the tuning gas, and wherein the electric field is outside of the plasma zone in the chamber;
• and
• supplying the tuning gas to the plasma zone in the chamber after flowing the tuning gas through the electric field.

A method for plasma processing of a microfeature workpiece, the method comprising:

• treating a surface of the workpiece in a plasma zone;
• dissociating and/or ionizing a tuning gas in a region radially outward of the plasma zone;
• and
• treating an edge of the workpiece with the dissociated and/or ionized tuning gas.