Technique for Monitoring and Controlling A PLasma Process

Abstract

A time-of-flight ion sensor for monitoring ion species in a plasma includes a housing. A drift tube is positioned in the housing. An extractor electrode is positioned in the housing at a first end of the drift tube so as to attract ions from the plasma. A plurality of electrodes is positioned at a first end of the drift tube proximate to the extractor electrode. The plurality of electrodes is biased so as to selectively attract ions to enter the drift tube and to drift towards a second end of the drift tube. An ion detector is positioned proximate to the second end of the drift tube. The ion detector detects arrival times associated with the at least the portion of the attracted ions.

1 . A time-of-flight ion sensor for monitoring ion species in a plasma, comprising:
 a drift tube disposed near an edge of the plasma;   an extractor electrode and a plurality of electrostatic lenses disposed at a first end of the drift tube, wherein the extractor electrode is biased to attract ions from a plasma in the plasma chamber, and wherein the plurality of electrostatic lenses cause at least one portion of the attracted ions to enter the drift tube and drift towards a second end of the drift tube within a limited divergence angle;   an ion detector disposed at the second end of the drift tube, wherein the ion detector detects arrival times associated with the at least one portion of the attracted ions; and   a housing for the extractor, the plurality of electrostatic lenses, the drift tube, and the ion detector, wherein the housing accommodates differential pumping between the ion sensor and the plasma chamber.   
   
   
       2 . The ion sensor according to  claim 1 , wherein the extractor electrode is biased at a plurality of potentials that perform attraction and repulsion of ions from the plasma. 
   
   
       3 . The ion sensor according to  claim 1 , wherein the extractor electrode is floating. 
   
   
       4 . The ion sensor according to  claim 1 , wherein the extractor electrode is RF biased. 
   
   
       5 . The ion sensor according to  claim 4 , wherein the extractor electrode is RF biased to cause one or more deposited materials on the extractor electrode to be sputtered. 
   
   
       6 . A time-of-flight ion sensor for monitoring ion species in a plasma, the time-of-flight ion sensor comprising:
 a housing;   a drift tube that is positioned in the housing;   an extractor electrode positioned in the housing at a first end of the drift tube, the extractor electrode being biased at a first potential to attract ions from the plasma and a second potential to repel ions from the extractor electrode;   a plurality of electrodes that are positioned at a first end of the drift tube proximate to the extractor electrode, the plurality of electrodes being biased so as to cause at least a portion of the attracted ions to enter the drift tube and to drift towards a second end of the drift tube; and   an ion detector that is positioned proximate to the second end of the drift tube, the ion detector detecting arrival times associated with the at least a portion of the attracted ions.   
   
   
       7 . A method for monitoring ion species in a plasma, the method comprising:
 applying a first bias voltage and a second bias voltage to an extractor electrode, the first and second bias voltage performing at least one of attraction and repulsion of ions;   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;   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.