Method of processing a workpiece by controlling a set of plasma parameters through a set of chamber parameters using surfaces of constant value

• US 20070029282A1
• Filed: 08/23/2006
• Published: 02/08/2007
• Est. Priority Date: 05/16/2003
• Status: Abandoned Application

• Current Assignee: Applied Materials Incorporated
• Original Assignee: Applied Materials Incorporated
• Inventors: Hoffman, Daniel
• Application Number:
  US11/508,522
• Publication Number:
  US 20070029282A1
• Time in Patent Office: Days
• US Class Current: 216/61
• 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

A workpiece is processed on a workpiece support pedestal in a plasma reactor chamber in accordance with user-selected values of plural plasma parameters of a group comprising ion density, wafer voltage, etch rate, wafer current, by controlling the chamber parameters of source power and bias power. The method includes the following steps: (a.) for each one of the plural plasma parameters, 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 space of which each of the chamber parameters is a dimension, and determining an intersection of the relevant surfaces, the intersection corresponding to a target value of source power and bias power; and (b.) setting the source power and bias power, respectively, to the target values. In preparation for the foregoing steps, a set of surfaces of constant value for each of the plasma parameters is stored in the memory, the set of surfaces corresponding to a set of constant values spanning a predetermined value range of the corresponding plasma parameter.

Claims

1. 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 of a group comprising ion density, wafer voltage, etch rate, wafer current, by controlling the chamber parameters of source power and bias power, 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 which each of said chamber parameters is a dimension, and determining an intersection of the relevant surfaces, said intersection corresponding to a target value of source power and bias power; and

b. setting said source power and bias power, respectively, to the 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 plural plasma parameters is two.

4. The method of claim 3 wherein said plural plasma parameters are wafer voltage and one of ion density and etch rate.

5. The method of claim 1 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.

6. The method of claim 5 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.

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 in said chamber, respectively, along said line.