WIDE DYNAMIC RANGE ION ENERGY BIAS CONTROL; FAST ION ENERGY SWITCHING; ION ENERGY CONTROL AND A PULSED BIAS SUPPLY; AND A VIRTUAL FRONT PANEL

• US 20140061156A1
• Filed: 08/27/2013
• Published: 03/06/2014
• Est. Priority Date: 08/28/2012
• 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, Kovalevskii, Dmitri
• Granted Patent: US 9,105,447 B2
• Time in Patent Office: Days
• US Class Current: 216/61
• CPC Class Codes: H01J 37/241 High voltage power supply or regulation circuits components H01J37/248
• CPC Class Codes: H01J 37/32091 the radio frequency energy being capacitively coupled to the plasma
• CPC Class Codes: H01J 37/32137 controlling of the discharge by modulation of energy
• CPC Class Codes: H01J 37/32146 Amplitude modulation, includes pulsing
• CPC Class Codes: H01J 37/32174 Circuits specially adapted for controlling the RF discharge

Abstract

This disclosure describes systems, methods, and apparatus for operating a plasma processing chamber. In particular, a periodic voltage function combined with an ion current compensation can be provided as a bias to a substrate support as a modified periodic voltage function. This in turn effects a DC bias on the surface of the substrate that controls an ion energy of ions incident on a surface of the substrate. A peak-to-peak voltage of the periodic voltage function can control the ion energy, while the ion current compensation can control a width of an ion energy distribution function of the ions. Measuring the modified periodic voltage function can provide a means to calculate an ion current in the plasma and a sheath capacitance of the plasma sheath. The ion energy distribution function can be tailored and multiple ion energy peaks can be generated, both via control of the modified periodic voltage function.

Claims

1. A method of operating a plasma processing chamber comprising:

sustaining a plasma in contact with a substrate on a substrate support within the plasma processing chamber;

accessing an effective capacitance, C₁, of the substrate support;

providing a modified periodic voltage function to the substrate support in order to effect a potential on a surface of the substrate, the modified period voltage function formed from a combination of a periodic voltage function and an ion current compensation, I_C; and

calculating ion current, I_I, in the plasma as a function of measurements of the modified periodic voltage function.

2. The method of claim 1, wherein the modified periodic voltage function comprises:

a rapidly increasing voltage called a first portion;

a substantially constant voltage starting at an end of the first portion and called a second portion;

a voltage step, Δ

V, below the substantially constant voltage starting at an end of the second portion and called the third portion; and

a sloped voltage starting Δ

V below the substantially constant voltage, starting at an end of the third portion, and called a fourth portion, the sloped voltage having a slope dV₀/dt controlled by the ion current compensation.

3. The method of claim 2, further comprising, adjusting the ion current compensation, I_C, until the following equation is met:

4. The method of claim 3, further comprising adjusting the ion current compensation, I_C, away from the ion current, I_I, so as to increase a width of the ion energy distribution function from the minimum.

5. The method of claim 3, wherein, when the equation is met, the following equation is true:

6. The method of claim 2, wherein ion current, I_I, is calculated by:

determining a first slope, dV₀₁/dt, for a first ion current compensation, I_C1;

determining a second slope, dV₀₂/dt, for a second ion current compensation, I_C2; and

calculating the ion current, I_I, as a function of the effective capacitance, C₁, the first slope, dV₀₁/dt, the second slope, dV₀₂/dt, the first ion current compensation, I_C1, and the second ion current compensation, I_C2.

7. The method of claim 6, wherein the ion current, I_I, is calculated via the following equation:

8. The method of claim 2, further comprising controlling an ion energy, eV, of ions incident on the substrate surface by controlling the voltage step, Δ

V, thereby effecting the potential on the substrate surface.

9. The method of claim 8, further comprising effecting two or more ion energy distribution peaks by providing two different voltage steps, Δ

V, for two adjacent cycles of the modified periodic voltage function.

10. The method of claim 2, further comprising calculating a capacitance of the plasma sheath, C₂, in real time and noninvasively.

11. The method of claim 10, wherein C₂ is calculated as a function of ion current, I_I.

12. The method of claim 11, wherein C₂ is calculated from the following equation:

13. The method of claim 1, further comprising monitoring an ion energy, eV, of ions incident on the substrate surface as a function of the voltage step, Δ

V.

14. The method of claim 13, wherein the ion energy, eV, is calculated from the voltage step, Δ

V, the effective capacitance, C₁, and the sheath capacitance, C₂, as follows;

15. The method of claim 1, wherein the modified periodic voltage function includes one or more periodically repeating fixed waveforms.

16. The method of claim 1, further comprising remotely and noninvasively monitoring a density of the plasma as a function of the ion current, I_I.

17. The method of claim 16, further comprising adjusting a peak-to-peak voltage of the periodic voltage function in response to the density of the plasma crossing one or more thresholds.

18. The method of claim 1, wherein accessing includes retrieval of the effective capacitance from a memory.

19. A plasma processing system comprising:

a substrate support in a plasma processing chamber supporting a substrate;

a substrate support bias supply providing a periodic voltage function;

an ion current compensation component providing an ion current compensation that is combined with the periodic voltage function to form a modified periodic voltage function that is provided to the substrate support and thereby effects a DC voltage on a surface of the substrate opposite to the substrate support, which in turn controls an ion energy of ions incident on the surface of the substrate opposite to the substrate support, the modified periodic voltage function having;

a first portion comprising a rapidly increasing voltage;

a second portion comprising a substantially constant voltage; and

a third portion comprising;

a sloped voltage having a starting voltage that is a voltage step, Δ

V, below the substantially constant voltage, the voltage step, Δ

V, corresponding to the ion energy, and a slope, dV₀/dt, controlled by the ion current compensation; and

a controller having a non-transitory, tangible computer readable storage medium encoded with processor readable instructions to;

access an effective capacitance of the substrate support, C₁;

measure the slope, dV₀/dt, for at least two ion current compensation values; and

calculate ion current, I_I, as a function of the effective capacitance, C₁, and the slope, dV₀/dt.

20. The plasma processing system of claim 19, wherein the controller is further configured to:

adjust the ion current compensation, I_C, until the following equation is met;

21. The plasma processing system of claim 19, wherein ion current, I_I, is calculated by:

determining a first slope, dV₀₁/dt, for a first ion current compensation, I_C1;

determining a second slope, dV₀₂/dt, for a second ion current compensation, I_C2; and

calculating the ion current, I_I, as a function of the effective capacitance, C₁, the first slope, dV₀₁/dt, the second slope, dV₀₂/dt, the first ion current compensation, I_C1, and the second ion current compensation, I_C2, without adjusting the ion current compensation, I_C, to be substantially equal to I.

22. The plasma processing system of claim 21, wherein the ion current, I_I, is calculated via the following equation:

23. The plasma processing system of claim 19, wherein the voltage step, Δ

V, is periodically varied between cycles of the modified periodic voltage function thereby resulting in two or more distinct ion energy distribution functions.

24. The plasma processing system of claim 19, wherein a duty cycle of the substrate support bias supply controls an ion flux of ions crossing the sheath and incident on the substrate surface, wherein the ion flux for each of one or more different ion energy distribution functions depends on a duty cycle of the modified periodic voltage function for each of one or more voltage steps, Δ

V.

25. The plasma processing system of claim 19, wherein the substrate support bias supply includes a first switch and a second switch, both arranged in parallel between a power source and an output of the substrate support bias supply.

26. The plasma processing system of claim 19, wherein the first switch selectively couples a bus voltage to the output and the second switch selectively couples the output to ground.

27. The plasma processing system of claim 19, wherein the controller:

opens the first switch and closes the second switch during a first period wherein a voltage ramps by a peak-to-peak voltage, V_PP, toward and slightly surpasses 0V;

closes the first switch and opens the second switch causing an instant drop in voltage, Δ

V, followed by a sloping region where a slope of the voltage is dV₀/dt; and

again opens the first switch and closes the second switch.

28. A non-transitory, tangible computer readable storage medium, encoded with processor readable instructions to perform a method for controlling characteristics of an ion energy distribution function of ions from a plasma that are incident on a substrate within a plasma processing chamber, the method comprising:

accessing an effective capacitance, C₁, of a substrate support supporting the substrate;

controlling a periodic voltage function provided by a substrate bias supply and an ion current compensation provided by an ion current compensation component, a combination of the periodic voltage function and the ion current compensation, being a modified periodic voltage function, is provided to the substrate support in order to effect a potential on a surface of the substrate opposite to the substrate support and thereby control an ion energy, eV, of ions incident on the substrate from the plasma; and

taking measurements of the modified periodic voltage function;

repeatedly calculating an ion current, I_I, in the plasma based on the measurements.

29. The non-transitory, tangible computer readable storage medium of claim 28, wherein the modified periodic voltage function includes a voltage step, Δ

V, followed by a sloped portion having a slope dV₀/dt.

30. The non-transitory, tangible computer readable storage medium of claim 29, wherein the ion current, I_I, is a function of the voltage step, Δ

V, and the slope of the sloped portion, dV₀/dt.

31. The non-transitory, tangible computer readable storage medium of claim 30, wherein the slope, dV₀/dt, is calculated using at least one voltage measurement from each of two different cycles of the modified periodic voltage function.

32. The non-transitory, tangible computer readable storage medium of claim 28, wherein the voltage step, Δ

V, corresponds to an average potential on the surface of the substrate opposite the substrate support and thereby effects an average ion energy, eV, of ions incident on the substrate.

33. The non-transitory, tangible computer readable storage medium of claim 32, wherein the slope of the sloped portion, dV₀/dt, is a function of an ion current compensation, I_C, from the ion current compensation component.

34. The non-transitory, tangible computer readable storage medium of claim 28, further comprising adjusting the ion current compensation, I_C, until it equals the ion current, I_I, thus minimizing a width of an ion energy distribution function via effecting a constant potential on the surface of the substrate opposite the substrate support.

35. The non-transitory, tangible computer readable storage medium of claim 28, further comprising adjusting the ion current compensation, I_C, in order to vary the potential on the surface of the substrate opposite the substrate support, thus increasing a width of the ion energy distribution function to a desired width.