Method of and apparatus for minimizing plasma instability in an RF processor
First Claim
1. A method of supplying an r.f. field to a plasma in a vacuum plasma chamber processing a workpiece, the r.f. field being supplied to the plasma by a reactive impedance element connected via a matching network to an r.f. source that can generate the r.f. field, the r.f. field having a frequency and power level sufficient to ignite a gas into the plasma and to maintain the plasma, the matching network including first and second variable reactances, the plasma having a tendency to change in an unstable manner which can adversely affect processing of the workpiece, the method comprising detecting that the plasma is tending to change in an unstable manner, and changing the value of said reactances of the matching network in response to the detecting step so the tendency of the plasma to change in an unstable manner which can adversely affect processing of the workpiece is overcome and the plasma is maintained in a stable state and a match is approached between the source and the impedance seen looking from the output terminals of the source.
1 Assignment
0 Petitions
Accused Products
Abstract
Variable reactances of a matching network connected between an r.f. source and a plasma load of a vacuum plasma chamber processing a workpiece are varied so a tendency of the plasma to change in an unstable manner which can adversely affect processing of the workpiece is avoided while matching is approached. The plasma tendency to change in an unstable manner is detected by monitoring an electrical parameter resulting from r.f. current flowing between the source and load via the network. The parameter can be (1) statistically based, e.g. variance of percent delivered power, or (2) amplitude modulation in one or both of the 2-20 kHz and 50-200 kHz ranges.
164 Citations
30 Claims
- 1. A method of supplying an r.f. field to a plasma in a vacuum plasma chamber processing a workpiece, the r.f. field being supplied to the plasma by a reactive impedance element connected via a matching network to an r.f. source that can generate the r.f. field, the r.f. field having a frequency and power level sufficient to ignite a gas into the plasma and to maintain the plasma, the matching network including first and second variable reactances, the plasma having a tendency to change in an unstable manner which can adversely affect processing of the workpiece, the method comprising detecting that the plasma is tending to change in an unstable manner, and changing the value of said reactances of the matching network in response to the detecting step so the tendency of the plasma to change in an unstable manner which can adversely affect processing of the workpiece is overcome and the plasma is maintained in a stable state and a match is approached between the source and the impedance seen looking from the output terminals of the source.
- 18. Apparatus for supplying r.f. energy to a plasma in a vacuum plasma chamber for processing a workpiece comprising a reactive impedance element positioned so it can be electrically coupled with a gas in the chamber, an r.f. electric source, a matching network having variable impedance properties connected between the source and the reactive impedance, the r.f. source having a frequency and power level to cause the reactive impedance element to supply an r.f. field to the gas to ignite the gas to the plasma, the plasma having a tendency to change in an unstable manner which adversely affects processing of the workpiece, and a controller for the variable impedance properties responsive to a function of an electric parameter resulting from current flowing between the source and load via the network, the electric parameter indicating that the plasma is tending to change in an unstable manner which can adversely affect processing of the workpiece, the controller varying the variable impedance properties in response to the parameter so the tendency of the plasma to change in an unstable manner which can adversely affect processing of the workpiece is overcome and the plasma is maintained in a stable state and a match is approached between the source and the impedance seen looking from the output terminals of the source.
-
30. A memory for use with a computer in combination with an apparatus for supplying r.f. energy to a plasma in a vacuum plasma chamber for processing a workpiece, the apparatus being such that a gas in the chamber is coupled with a reactive impedance element for coupling an r.f. field to the gas, the r.f. field being such that it can excite the gas to the plasma, the reactive impedance element being connected via a matching network to an r.f. source that can generate the r.f. field, the matching network including variable impedance properties, the matching network being coupled to a load including the reactive impedance element and the plasma, the plasma having a tendency to change in an unstable manner which adversely affects processing of the workpiece, the apparatus deriving signals indicative of values of electrical parameters resulting from current flowing between the source and the load via the network, the memory comprising a medium storing signals for controlling the computer so the computer can (a) derive signals indicative of the plasma being in an unstable state in response to the signals indicative of the values of the electrical parameters, and (b) in response to the plasma being indicated as being at the onset of the unstable state, control the value of the variable impedance properties of the matching network so the plasma unstable tendency is substantially avoided and the plasma is maintained in a stable state while an impedance match is approached between the source and the impedance seen looking from the output terminals of the source.
Specification