Frequency tuning for pulsed radio frequency plasma processing

Patent metadata

Field	Value
Publication number	US-9544987-B2
Application number	US-201414320268-A
Country	US
Kind code	B2
Filing date	Jun 30, 2014
Priority date	Jun 30, 2014
Publication date	Jan 10, 2017
Grant date	Jan 10, 2017

Abstract

This disclosure describes systems, methods, and apparatus for pulsed RF power delivery to a plasma load for plasma processing of a substrate. In order to maximize power delivery, a calibration phase using a dummy substrate or no substrate in the chamber, is used to ascertain a preferred fixed initial RF frequency for each pulse. This fixed initial RF frequency is then used at the start of each pulse during a processing phase, where a real substrate is used and processed in the chamber.

First claim

What is claimed is:

1. A method of selecting a fixed initial RF frequency for each of a plurality of RF pulses provided to a plasma load, the method comprising:
providing pulsed RF power to a plasma load, where each pulse comprises RF power having a controllable frequency, and where a plasma having the plasma load interacts with a dummy substrate, or no substrate, in a plasma chamber;
tuning an initial RF frequency for each pulse in a string of pulses, pulse to pulse, in a calibration process, by minimizing a difference between a characteristic indicative of the pulsed RF power at a start of each pulse and a desired characteristic of the pulsed RF power at a start of each pulse until the difference between the characteristic for a start to two consecutive pulses is below a threshold; then
selecting the initial RF frequency as a fixed initial RF frequency for use in a processing run using a real substrate; and
tuning the RF frequency during processing within each pulse but returning to the fixed initial RF frequency at a start of each pulse.

2. The method of claim 1 , wherein the characteristic indicative of the pulsed RF power is reflected power.

3. The method of claim 1 , wherein the characteristic indicative of the pulsed RF power is load impedance power.

4. The method of claim 1 , wherein the characteristic indicative of the pulsed RF power is a density of the plasma.

5. The method of claim 1 , wherein the processing run includes providing pulsed RF power to the plasma load where an initial RF frequency at a start of each pulse is set to the fixed initial RF frequency.

6. A non-transitory, tangible computer readable storage medium, encoded with processor readable instructions to perform a method for frequency tuning a power source to optimize delivered power to a plasma load, the method comprising:
in a calibration phase,
tuning an initial RF frequency at a start of each pulse in a string of RF pulses, pulse to pulse, until a difference between a characteristic indicative of power at the start of each pulse and a desired characteristic of the power at the start of each pulse, for a start to two consecutive pulses, is below a threshold; then
selecting the initial RF frequency as a fixed initial RF frequency to be used during a processing phase; and

in the processing phase,
setting an initial RF frequency for all pulses in the processing phase equal to the fixed initial RF frequency selected during the calibration phase; and
tuning the RF frequency of pulsed RF power during each pulse, but returning to the fixed initial RF frequency at a start of each pulse.

7. The non-transitory, tangible computer readable storage medium of claim 6 , wherein the characteristic indicative of the pulsed RF power is reflected power.

8. The non-transitory, tangible computer readable storage medium of claim 6 , wherein the characteristic indicative of the pulsed RF power is load impedance power.

9. The non-transitory, tangible computer readable storage medium of claim 6 , wherein the characteristic indicative of the pulsed RF power is a density of the plasma.

10. A power delivery system comprising:
a power source configured to provide pulsed RF power to a plasma load via a matching network;
a sensor configured to sample a characteristic indicative of the pulsed RF power;
a controller in communication with the sensor and the power source and executable to:
in a calibration phase,
tuning an initial RF frequency at a start of each pulse in a string of RF pulses, pulse to pulse, until a difference between a characteristic indicative of power at the start of each pulse and a desired characteristic of the power at the start of each pulse, for a start to two consecutive pulses, is below a threshold; then
selecting the initial RF frequency as a fixed initial RF frequency to be used during a processing phase; and

in the processing phase,
setting an initial RF frequency for all pulses in the processing phase equal to the fixed initial RF frequency selected during the calibration phase; and
tuning the RF frequency of pulsed RF power during each pulse, but returning to the fixed initial RF frequency at a start of each pulse.

11. The power delivery system of claim 10 , wherein the sensor is a reflected power sensor.

12. The power delivery system of claim 11 , wherein the sensor is a directional coupler.

13. The power delivery system of claim 10 , wherein the sensor is a delivered power sensor.

14. The power delivery system of claim 10 , wherein the sensor is an impedance sensor.

15. The power delivery system of claim 10 , wherein the sensor is a plasma density sensor.

16. The power delivery system of claim 10 , wherein the power source is in communication with a switching circuit that converts RF power from the power source to the pulsed RF power.

17. The power delivery system of claim 10 , wherein the sensor is part of an oscilloscope.

Assignees

• Advanced Energy Ind Inc

Inventors

• Mueller Michael
• Choi Myeong Yeol

Classifications

• H01J37/32146

  Amplitude modulation, includes pulsing · CPC title

• H01J37/32183

  Matching circuits · CPC title

• H01J37/3299

  Feedback systems · CPC title

• H01J37/32926

  Software, data control or modelling · CPC title

• H01J37/32174

  Circuits specially adapted for controlling the RF discharge · CPC title