Plasma processing method and apparatus with control of rf bias
First Claim
1. A method of controlling an a.c. plasma treating a workpiece in a vacuum plasma processing chamber, the workpiece being on a workpiece holder having an electrode, the method being performed in accordance with a recipe having a set of parameters including at least one gas supplied to the chamber, flow rate of the gas supplied to the chamber, pressure range in the chamber, power range supplied to an excitation reactance for the plasma and power range supplied to the electrode, the method comprisingsupplying a.c. from a first a.c. source to the plasma via a first circuit including an excitation reactance and a first matching network including first and second variable reactances, sensing a first function related to a load including the plasma as seen by the first circuit, controlling the first and second reactances in response to the sensed first function to maintain a predetermined relation between functions of (a) the output impedance of the first source and (b) the impedance the first source drives, supplying a.c. from a second a.c. source to the plasma via the electrode and a second matching network including third and fourth variable reactances, sensing a second function related to the impedance of the plasma, controlling the third and fourth variable reactances in response to the sensed second function to maintain a substantially matched condition between the output impedance of the second source and the impedance the second source drives, power reflected back to the second source having a tendency to have a step change as a result of a small variation in the value of at least one of the third and fourth reactances from the values which provide a match between the output impedance of the second source and the load the second source drives, the at least one small change resulting from an incremental change in at least one of the parameters while the one parameter remains in a range consistent with the recipe, and overcoming the tendency for the step change by varying the output power of the second source in response to a function of plasma impedance, the second source output power being varied at a speed much faster than the speed that the third and fourth reactances change to produce the tendency to have the step change.
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Accused Products
Abstract
A tendency for a discontinuity to occur in the amount of power reflected back to an r.f. bias source of a vacuum plasma processor is overcome by controlling the r.f. bias source output power so the power delivered to plasma in a vacuum processing chamber remains substantially constant. The r.f bias source output power is changed much faster than changes in capacitors of a matching network connecting the r.f. bias power source to an electrode of a workpiece holder processor. A capacitive impedance component of the plasma is determined by optically measuring the thickness of a plasma sheath in the chamber.
76 Citations
19 Claims
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1. A method of controlling an a.c. plasma treating a workpiece in a vacuum plasma processing chamber, the workpiece being on a workpiece holder having an electrode, the method being performed in accordance with a recipe having a set of parameters including at least one gas supplied to the chamber, flow rate of the gas supplied to the chamber, pressure range in the chamber, power range supplied to an excitation reactance for the plasma and power range supplied to the electrode, the method comprising
supplying a.c. from a first a.c. source to the plasma via a first circuit including an excitation reactance and a first matching network including first and second variable reactances, sensing a first function related to a load including the plasma as seen by the first circuit, controlling the first and second reactances in response to the sensed first function to maintain a predetermined relation between functions of (a) the output impedance of the first source and (b) the impedance the first source drives, supplying a.c. from a second a.c. source to the plasma via the electrode and a second matching network including third and fourth variable reactances, sensing a second function related to the impedance of the plasma, controlling the third and fourth variable reactances in response to the sensed second function to maintain a substantially matched condition between the output impedance of the second source and the impedance the second source drives, power reflected back to the second source having a tendency to have a step change as a result of a small variation in the value of at least one of the third and fourth reactances from the values which provide a match between the output impedance of the second source and the load the second source drives, the at least one small change resulting from an incremental change in at least one of the parameters while the one parameter remains in a range consistent with the recipe, and overcoming the tendency for the step change by varying the output power of the second source in response to a function of plasma impedance, the second source output power being varied at a speed much faster than the speed that the third and fourth reactances change to produce the tendency to have the step change.
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11. Apparatus for processing a workpiece comprising
a vacuum plasma processor chamber having (a) a workpiece holder including an electrode for electrostatically supplying electric energy to the workpiece, (b) a first port for supplying an ionizable gas to the chamber, (c) a second port for connecting a vacuum pump arrangement to the chamber; -
an excitation reactance for supplying sufficient electric and magnetic energy to the ionizable gas to excite the gas to a plasma;
a first a.c. source;
a first matching network connected between the first a.c. source and the excitation reactance, the first matching network including first and second variable reactances;
a sensing arrangement responsive to the plasma impedance;
a second a.c. source;
a second matching network connected between the second a.c. source and the electrode, the second matching network including third and fourth variable reactances;
a controller for (a) the vacuum pump arrangement to control the vacuum in the chamber, (b) flow rate of gas supplied to the first port, (c) output power of the first a.c. source, (d) output power of the second a.c. source, and (e) the values of the first, second, third and fourth variable impedances, the controller including an input device and a memory storing several recipes for different conditions in the chamber, each recipe including a set of parameters for preset values of the vacuum, flow rate, first source output power and second source output power, the controller responding to the input device for accessing the memory for causing the vacuum in the chamber, gas flow rate and output power of the first and second sources to be at the preset values within predetermined ranges associated with a selected one of the recipes, the controller responding to the sensing arrangement for (a) controlling the first and second reactances to obtain a substantial impedance match between the first source and the impedance seen looking from the first matching network into the excitation reactance while the plasma is loading the excitation reactance and (b) controlling the third and fourth reactances to obtain a substantial impedance match between the second source and the impedance seen looking from the second matching network into the electrode while the plasma is loading the excitation reactance electrode;
the power reflected back to the second source having a tendency to have a step change as a result of a small variation in the value of at least one of the third and fourth reactances from the values which provide a match between the output impedance of the second source and the load the second source drives, the at least one small change resulting from an incremental change in at least one of the parameters while the one parameter remains in its range for the single set of parameters for the selected recipe;
the controller being arranged for responding to the sensing arrangement for overcoming the tendency for the step change by varying the output power of the second source in response to a function of plasma impedance, the second source output power being variable at a speed much faster than the speed that the third and fourth reactances change to produce the tendency to have the step change. - View Dependent Claims (12, 13, 14, 15, 16, 17, 18, 19)
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Specification