Method of controlling a chamber based upon predetermined concurrent behavoir of selected plasma parameters as a function of selected chamber paramenters

• US 20070095788A1
• Filed: 12/11/2006
• Published: 05/03/2007
• Est. Priority Date: 05/16/2003
• Status: Active Grant

• Current Assignee: Applied Materials Incorporated
• Original Assignee: Applied Materials Incorporated
• Inventors: Hoffman, Daniel, Gold, Ezra
• Granted Patent: US 7,795,153 B2
• Time in Patent Office: Days
• US Class Current: 216/59
• CPC Class Codes: H01J 37/32174 Circuits specially adapted for controlling the RF discharge
• CPC Class Codes: H01J 37/32935 Monitoring and controlling tubes by information coming from the object and/or discharge

Abstract

The invention involves a method of processing a workpiece on workpiece support pedestal in a plasma reactor chamber in accordance with user-selected values of plural (i.e., N) plasma parameters by controlling plural chamber parameters. The plasma parameters may be selected from of a group including ion density, wafer voltage, etch rate, wafer current and possibly other plasma parameters. The chamber parameters may be selected from a group including source power, bias power, chamber pressure, magnet coil current of different coils, gas flow rate in different gas injection zones, gas species composition in different gas injection zones, and possibly other chamber parameters. The method begins with a first step carried out for each one of the selected plasma parameters. This first step consists of fetching from a memory a relevant surface of constant value corresponding to the user-selected value of the one plasma parameter, the surface being defined in a N-dimensional space of which each of the N chamber parameters is a dimension. This step further includes determining an intersection of these relevant surfaces, the intersection corresponding to a target value of each of the N chamber parameter. The method further includes setting each of the N chamber parameters to the corresponding target value.

Claims

1. A method of processing a workpiece on workpiece support pedestal in a plasma reactor chamber in accordance with user-selected values of plural plasma parameters selected from a group comprising ion density, wafer voltage, etch rate, wafer current, by controlling chamber parameters selected from a group comprising source power, bias power, chamber pressure, magnet coil current, gas flow rates in respective zones and gas composition in respective zones, said method comprising:

a. for each one of said plural plasma parameters, fetching from a memory a relevant surface of constant value corresponding to the user-selected value of said one plasma parameter, said surface being defined in a space of a dimensionality equal to the number of said selected chamber parameters, and determining an intersection of the relevant surfaces, said intersection corresponding to respective target values of the selected chamber parameters; and

b. setting the values of said selected chamber parameters to the respective target values.

2. The method of claim 1 wherein said memory is provided as a component of said reactor chamber, said method further comprising the initial step of storing in said memory a set of surfaces of constant value for each of said plasma parameters, said set of surfaces corresponding to a set of constant values spanning a predetermined value range of the corresponding plasma parameter.

3. The method of claim 1 wherein the number of said selected chamber parameters is greater than three.

4. The method of claim 3 wherein the number of said selected chamber parameters is greater than four.

5. The method of claim 1 further comprising:

subsequently controlling plasma bias power in a feedback control loop by sensing a difference between the user-selected value of wafer voltage and a concurrently measured value of wafer voltage and changing the plasma bias power to reduce said difference.

6. The method of claim 5 further comprising:

subsequently controlling plasma source power in a feedback control loop by sensing a difference between the user-selected value of plasma ion density or etch rate and a measured value of plasma ion density or etch rate and changing the plasma source power to reduce said difference.

7. The method of claim 6 further comprising obtaining said measured values of wafer voltage and plasma ion density by the steps of:

sampling values of RF electrical parameters at an input end of a transmission line coupling RF bias power to an electrode within said wafer support pedestal, said electrode being connected to an output end of the transmission line;

computing said measured value of wafer voltage from the sampled values of the RF electrical parameters; and

computing said measured value of plasma ion density or etch rate from the sampled values of the RF electrical parameters.

8. The method of claim 7 wherein said RF electrical parameters comprise an input impedance, an input current and an input voltage.

9. The method of claim 8 wherein the step of computing comprises:

computing a junction admittance of a junction between said transmission line and said electrode within the wafer pedestal from said input impedance, input current and input voltage and from parameters of the transmission line;

providing shunt electrical quantities of a shunt capacitance between the electrode and a ground plane;

providing load electrical quantities of a load capacitance between the electrode and a wafer on the pedestal; and

computing said etch rate, plasma ion density and wafer voltage from said junction admittance, said shunt electrical quantities, said load electrical quantities and a frequency of RF bias power applied to said electrode.

10. The method of claim 9 wherein said parameters of said transmission line comprise a length of said transmission line, a characteristic impedance of said transmission line and a complex loss factor of said transmission line.

11. The method of claim 10 wherein:

said shunt electrical quantities are computed from the size of an electrode-to-ground gap length, an area of said wafer, an electrode-to-ground dielectric constant and an electrode-to-ground conductive loss component;

said load electrical quantities are computed from an electrode-to-wafer gap length, an area of the wafer, an electrode-to-wafer dielectric constant and an electrode-to-wafer conductive loss component.

12. The method of claim 11 wherein the step of computing said etch rate, plasma ion density and wafer voltage comprises:

first computing said wafer voltage and an imaginary part of a plasma admittance comprising a plasma susceptance, and computing said ion density and etch rate from said wafer voltage and said plasma susceptance.

13. A method of processing a workpiece on a workpiece support pedestal in a plasma reactor chamber in accordance with user-selected values of plural plasma parameters selected from a group comprising ion density, wafer voltage, etch rate and wafer current, by controlling chamber parameters selected from a group comprising source power, bias power, chamber pressure, magnet coil current and gas flow rate, the number of said plural plasma parameters being less than the number of said chamber parameters, said method comprising:

a. for each one of said plural plasma parameters, fetching a relevant surface of constant value corresponding to the user-selected value of said one plasma parameter, and determining an intersection of the relevant surfaces which defines a line in a space whose dimensionality is equal to the number of said selected chamber parameters; and

b. varying said selected chamber parameters along said line.

14. The method of claim 13 further comprising:

subsequently controlling plasma bias power by sensing a difference between the user-selected value of wafer voltage and a measured value of wafer voltage and changing the plasma bias power to reduce said difference.

15. The method of claim 14 further comprising:

subsequently controlling plasma source power by sensing a difference between the user-selected value of plasma ion density or etch rate and a measured value of plasma ion density or etch rate and changing the plasma source power to reduce said difference.

16. The method of claim 15 further comprising obtaining said measured values of wafer voltage and plasma ion density or etch rate by the steps of:

sampling values of RF electrical parameters at an input end of a transmission line coupling RF bias power to an electrode within said wafer support pedestal, said electrode being connected to an output end of the transmission line;

computing said measured value of wafer voltage from the sampled values of the RF electrical parameters; and

computing said measured value of plasma ion density or etch rate from the sampled values of the RF electrical parameters.

17. The method of claim 16 wherein said RF electrical parameters comprise an input impedance, an input current and an input voltage and the step of computing comprises:

computing a junction admittance of a junction between said transmission line and said electrode within the wafer pedestal from said input impedance, input current and input voltage and from parameters of the transmission line;

providing shunt electrical quantities of a shunt capacitance between the electrode and a ground plane;

providing load electrical quantities of a load capacitance between the electrode and a wafer on the pedestal; and

computing said wafer voltage and etch rate or plasma ion density from said junction admittance, said shunt electrical quantities, said load electrical quantities and a frequency of RF bias power applied to said electrode.

18. The method of claim 17 wherein the step of computing said wafer voltage and etch rate or plasma ion density comprises:

first computing said wafer voltage and an imaginary part of a plasma admittance comprising a plasma susceptance, and computing said ion density and etch rate from said wafer voltage and said plasma susceptance.