METHOD OF CONTROLLING THE SWITCHED MODE ION ENERGY DISTRIBUTION SYSTEM

• US 20120319584A1
• Filed: 08/28/2012
• Published: 12/20/2012
• Est. Priority Date: 08/29/2010
• Status: Active Grant

• Current Assignee: AES Global Holdings Pte Ltd. (Advanced Energy Industries, Inc. (China))
• Original Assignee: Advanced Energy Industries Incorporated
• Inventors: Brouk, Victor, Hoffman, Daniel J., Carter, Daniel
• Granted Patent: US 9,362,089 B2
• Time in Patent Office: Days
• US Class Current: 315/111.21
• CPC Class Codes: H01J 37/32009 Arrangements for generation of plasma specially adapted for examination or treatment of objects, e.g. plasma sources plasma generation in general H05H1/24
• 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
• CPC Class Codes: H01J 37/3299 Feedback systems

Abstract

Systems, methods and apparatus for regulating ion energies in a plasma chamber and chucking a substrate to a substrate support are disclosed. An exemplary method includes placing a substrate in a plasma chamber, forming a plasma in the plasma chamber, controllably switching power to the substrate so as to apply a periodic voltage function (or a modified periodic voltage function) to the substrate, and modulating, over multiple cycles of the periodic voltage function, the periodic voltage function responsive to a defined distribution of energies of ions at the surface of the substrate so as to effectuate the defined distribution of ion energies on a time-averaged basis.

Claims

1. An apparatus for providing a modified periodic voltage function to an electrical node, the electrical node being configured for coupling to a substrate support of a plasma processing chamber, the apparatus comprising:

a power supply providing a periodic voltage function to the electrical node, the periodic voltage function having pulses and a portion between the pulses;

an ion current compensation component providing an ion current compensation to modify a slope of the portion between the pulses thus forming a modified periodic voltage function; and

a controller in communication with the switch-mode power supply and the ion current compensation component and configured to identify a value of the ion current compensation that, if provided to the electrical node, will result in a defined ion energy distribution function of ions reaching a surface of the substrate.

2. The apparatus of claim 1, wherein the power supply is a switch-mode power supply.

3. The apparatus of claim 2, wherein the switch-mode power supply includes one or more switching components.

4. The system of claim 1, wherein the controller samples two or more voltages from the modified periodic voltage function and calculates a slope, dV₀/dt, of the two or more voltages.

5. The system of claim 4, wherein the slope, dV₀/dt, is calculated based on two or more voltages sampled from a portion of the modified periodic voltage function between pulses of the modified periodic voltage function.

6. The system of claim 5, wherein the controller is configured to adjust the switch-mode power supply voltage a first time in order to establish an average ion energy of a first set of ions reaching the surface of the substrate.

7. The system of claim 6, wherein the controller is configured to adjust the switch-mode power supply voltage a second time in order to establish an average ion energy of a second set of ions reaching the surface of the substrate.

8. The system of claim 5, wherein the switch-mode power supply is configured to adjust a voltage step of the modified periodic voltage function in order to establish the average ion energy of the first set of ions reaching the surface of the substrate.

9. The system of claim 5, wherein the switch-mode power supply is configured to adjust a peak-to-peak voltage of the modified periodic voltage function in order to establish the average ion energy of the first set of ions reaching the surface of the substrate.

10. They system of claim 5, wherein switching of the one or more switching components is timed so as to affect the slope of the portion of the modified periodic voltage function between the pulses of the modified periodic voltage function.

11. The apparatus of claim 1, wherein the controller adjusts an amplitude of the ion current compensation until the defined ion energy distribution function of ions reaching the surface of the substrate is achieved.

21. The method of claim 10, wherein the ion current compensation, I_C, is linearly related to the ion current, I_I, according to the following equation:

22. The method of claim 21, wherein the effective capacitance, C₁, varies in time.

23. The method of claim 21, wherein the ion current compensation, I_c, varies in time.

12. A method for providing a modified periodic voltage function to an electrical node, the electrical node configured for electrically-coupling to a substrate support of a plasma processing chamber, the method comprising:

providing an ion current compensation, I_C, to the electrical node;

providing a periodic voltage function to the electrical node, the periodic voltage function being modified by the ion current compensation, I_C, to form the modified periodic voltage function;

providing the modified periodic voltage function to the electrical node, the modified periodic voltage function having pulses and a portion between the pulses;

accessing an effective capacitance value, C₁, representing at least a capacitance of the substrate support;

determining a slope, dV_o/dt, of the portion between the pulses of the modified periodic voltage function; and

identifying a value of the ion current compensation, I_C, that will result in a defined ion energy distribution function of ions reaching a surface of the substrate, wherein the identifying is a function of the effective capacitance, C₁, and the slope, dV₀/dt, of the portion between the pulses.

13. The method of claim 12, wherein the defined ion energy distribution is a narrow ion energy distribution.

14. The method of claim 12, wherein the value of the ion current compensation, I_C, that will result in the defined ion energy distribution function of ions reaching the surface of the substrate is a value that meets a function ƒ

as follows;

15. The method of claim 14, further comprising:

setting the ion current compensation, I_C, to a first value;

determining a sign of the function ƒ

; and

increasing the ion current compensation, I_C, if the sign of the function ƒ

is positive and decreasing the ion current compensation, I_C, if the sign of the function ƒ

is negative.

16. The method of claim 12, wherein the identifying includes sampling a voltage of the portion between the pulses of the modified periodic voltage function at two or more times.

17. The method of claim 16, wherein the identifying includes calculating the slope, dV₀/dt, from the voltage sampled at the two or more times.

18. The method of claim 17, wherein the identifying includes calculating the slope, dV₀/dt, for two or more cycles of the modified periodic voltage function, where each of the two or more cycles is associated with a different value of the ion current compensation, I_C.

19. The method of claim 16, wherein the identifying includes sampling a voltage of the portion between the pulses of the modified periodic voltage function during a first cycle and during a second cycle, and calculating the slope, dV₀/dt, from at least these two sampled voltages.

20. The method of claim 12, wherein the ion current compensation, I_C, is linearly related to an ion current, I_I, across a plasma sheath of a plasma formed in the plasma processing chamber.

24. The method of claim 12, further comprising providing the modified periodic voltage function to the electrical node so that ions reach the surface of the substrate with a first ion energy.

25. The method of claim 24, wherein the modified periodic voltage function has a first voltage step that corresponds to the first ion energy.

26. The method of claim 25, further comprising providing the modified periodic voltage function to the electrical node with a second value of the ion current compensation, I_C, so as to broaden the ion energy distribution function.

27. The method of claim 25, wherein the first voltage step and the second voltage step are provided in adjacent cycles of the modified periodic voltage function.

28. The method of claim 24, wherein the providing has negligible effect on a density of the plasma.

29. A method comprising:

applying a modified periodic voltage function to an electrical node, the modified periodic voltage function comprising a periodic voltage function modified by an ion current compensation, wherein the electrical node is configured for coupling to a substrate support coupled to a substrate in a plasma processing chamber;

sampling at least one cycle of the modified periodic voltage function to generate voltage data points;

estimating a value of a first ion energy for ions reaching a surface of the substrate, the estimating based on the voltage data points; and

adjusting the modified periodic voltage function until the first ion energy equals the defined ion energy.

30. The method of claim 29, further comprising sampling at least one cycle of the modified periodic voltage function and estimating the value of the first ion energy after each voltage increment of the adjusting.

31. The method of claim 29, wherein the estimating is a function of ion current.

32. The method of claim 31, wherein the ion current is a function of the ion current compensation.

33. The method of claim 32, wherein the following equation is used in the estimating a value of the first ion energy:

34. The method of claim 33, wherein the adjusting comprises adjusting the step voltage, Δ

V, of the modified periodic voltage function until the first ion energy equals the defined ion energy.

35. The method of claim 29, further comprising changing a first value of the ion current compensation to a second value so as to broaden a width of a distribution of the ion energy.

36. The method of claim 29, wherein the adjusting comprises adjusting a bias supply voltage until the first ion energy equals the defined ion energy.

37. A method comprising:

providing a modified periodic voltage function to an electrical node, where the electrical node is configured for coupling to a substrate support of a plasma processing chamber;

sampling at least two voltages from the modified periodic voltage function at a first time and at a second time;

calculating a slope of the at least two voltages as dV/dt;

comparing the slope to a reference slope known to correspond to a ion energy distribution function width; and

adjusting the modified periodic voltage function so that the slope approaches the reference slope.

38. The method of claim 37, wherein the first time occurs during a first cycle of the modified periodic voltage function and the second time occurs during a second cycle of the modified periodic voltage function.

39. The method of claim 37, wherein the first and second times occur during a same cycle of the modified periodic voltage function.

40. The method of claim 37, wherein the sampling is performed at a sampling rate of at least 400 kHz.

41. A non-transitory, tangible computer readable storage medium, encoded with processor readable instructions to perform a method for identifying a defined ion current compensation, I_C, the method comprising:

sampling a modified periodic voltage function given the ion current compensation, I_C, having a first value;

sampling a modified periodic voltage function given the ion current compensation, I_C, having a second value;

accessing an effective capacitance, C₁, for the plasma processing chamber;

determining a slope, dV₀/dt, of the modified periodic voltage function based on the first and second sampling; and

calculating a third value of the ion current compensation, I_C, that makes the following equation true;

42. The non-transitory, tangible computer readable storage medium of claim 41, further comprising calculating a sheath voltage across a plasma sheath of a plasma of the plasma processing chamber.