Technique for monitoring and controlling a plasma process

A method for monitoring ion species in a plasma used for processing a substrate, the method comprising:

• applying a bias voltage to an extractor electrode, the bias voltage performing at least one of attraction and repulsion of ions from the plasma;
• applying a voltage signal to at least one of a plurality of electrostatic electrodes that are positioned proximate to the extractor electrode, the voltage signal causing at least a portion of the attracted ions to drift though a drift tube;
• applying a blocking voltage to at least one electrode of the extractor electrode and the electrostatic electrodes at a pre determined time in order to prevent ions from traveling into the drift tube during the pre determined time;
• detecting arrival times at an end of the drift tube, the arrival times being associated with the at least a portion of attracted ions;
• and
• determining information about the plasma from the arrival times.

A time-of-flight ion sensor for monitoring ion species in a plasma used for processing a substrate comprising:

• a means for applying a bias voltage to an extractor electrode, the bias voltage performing at least one of attraction and repulsion of ions from the plasma;
• a means for applying a voltage signal to at least one of a plurality of electrodes that are positioned proximate to the extractor electrode, the voltage signal causing at least a portion of the attracted ions to drift though a drift tube that is configured as an energy analyzer;
• and
• a means for detecting arrival times at an end of the drift tube, wherein the arrival times are associated with the at least a portion of attracted ions.