Method and system for automated frequency tuning of radiofrequency (RF) signal generator for multi-level RF power pulsing

Patent metadata

Field	Value
Publication number	US-12300463-B2
Application number	US-202017607301-A
Country	US
Kind code	B2
Filing date	May 9, 2020
Priority date	May 10, 2019
Publication date	May 13, 2025
Grant date	May 13, 2025

Abstract

A two-dimensional frequency search grid is defined by a first coordinate axis representing an operating frequency setpoint of an RF signal generator in a first operational state and a second coordinate axis representing an operating frequency setpoint of the RF signal generator in a second operational state. The RF signal generator has a first output power level in the first operational state and a second output power level in the second operational state. The RF signal generator operates in an multi-level RF power pulsing mode by cyclically alternating between the first operational state and the second operational state. An automated search process is performed within the two-dimensional frequency search grid to simultaneously determine an optimum value for the operating frequency setpoint of the RF signal generator in the first operational state and an optimum value for the operating frequency setpoint of the RF signal generator in the second operational state.

First claim

What is claimed is:

1. A method for automated frequency tuning of a radiofrequency (RF) signal generator for operating in a multi-level RF power pulsing mode, comprising:
defining a two-dimensional frequency search grid having a first coordinate axis representing an operating frequency setpoint of the RF signal generator in a first operational state and having a second coordinate axis representing an operating frequency setpoint of the RF signal generator in a second operational state, the RF signal generator having a first output power level in the first operational state and a second output power level in the second operational state, the first and second output power levels being different from each other, the RF signal generator programmed to operate in the multi-level RF power pulsing mode by cyclically alternating between the first operational state and the second operational state;
performing an automated search process within the two-dimensional frequency search grid to simultaneously determine a first optimum value for the operating frequency setpoint of the RF signal generator in the first operational state and a second optimum value for the operating frequency setpoint of the RF signal generator in the second operational state, wherein the automated search process is a triangulation search process performed within the two-dimensional frequency search grid to determine an optimum set of frequency coordinates within the two-dimensional frequency search grid that correspond to a minimization of a cost function defined to characterize RF power delivery from the RF signal generator to a plasma load, the optimum set of frequency coordinates including the first optimum value and the second optimum value; and
setting the RF signal generator to operate using the first optimum value and the second optimum value.

2. The method as recited in claim 1 , wherein the automated search process is directed by a control system of a plasma processing system that includes the RF signal generator.

3. The method as recited in claim 2 , wherein the automated search process includes multiple iterations with each iteration including operation the RF signal generator in the multi-level RF power pulsing mode to generate a plasma in the plasma processing system using a different set of operating frequency setpoint coordinates within the two-dimensional frequency search grid.

4. The method as recited in claim 3 , wherein each iteration includes empirical evaluation of RF power delivery from the RF signal generator to the plasma.

5. The method as recited in claim 3 , wherein the plasma is generated in exposure to a substrate in each iteration, the substrate having a film of a target material present on a top surface of the substrate that is exposed to the plasma.

6. The method as recited in claim 3 , wherein the RF signal generator is a bias RF signal generator, and wherein the plasma processing system includes a primary RF signal generator that is separate from the bias RF signal generator, and wherein each iteration includes operation of the primary RF signal generator to generate additional plasma in the plasma processing system.

7. The method as recited in claim 3 , wherein the RF signal generator is a primary RF signal generator.

8. The method as recited in claim 7 , wherein the plasma processing system includes a bias RF signal generator that is separate from the primary RF signal generator, and wherein each iteration is performed with the bias RF signal generator turned off.

9. The method as recited in claim 1 , wherein the triangulation search process includes evaluation of the cost function at vertices of sequentially formed equilateral triangles within the two-dimensional frequency search grid.

10. The method as recited in claim 9 , wherein evaluation of the cost function for a given vertex of a given equilateral triangle within the two-dimensional frequency search grid is performed by operating the RF signal generator in the multi-level RF power pulsing mode for a period of time using frequency coordinates for the given vertex within the two-dimensional frequency search grid as operating frequency setpoints for the RF signal generator in the first and second operational states.

11. The method as recited in claim 10 , wherein the period of time is less than or equal to about 5 seconds.

12. The method as recited in claim 10 , wherein evaluation of the cost function for the given vertex of the given equilateral triangle within the two-dimensional frequency search grid includes computing a sum of an average of a reflection coefficient for RF signals generated by the RF signal generator in the first operational state over the period of time, and an average of a reflection coefficient for RF signals generated by the RF signal generator in the second operational state over the period of time, and an average of a relative error in voltage generated by the RF signal generator in the first operational state over the period of time, and an average of a relative error in voltage generated by the RF signal generator in the second operational state over the period of time.

13. The method as recited in claim 12 , wherein the triangulation search process further includes a process of sequentially forming equilateral triangles within the two-dimensional frequency search grid by identifying a particular vertex of a current equilateral triangle that has a largest cost function value among three vertices of the current equilateral triangle, and by moving the particular vertex of the current equilateral triangle in a straight line through a centroid of the current equilateral triangle while maintaining positions of the two other vertices of the current equilateral triangle until the particular vertex reaches a new vertex position within the two-dimensional frequency search grid corresponding to formation of a new equilateral triangle defined by the new vertex position and the positions of the two other vertices whose positions were maintained.

14. The method as recited in claim 13 , wherein the triangulation search process continues the process of sequentially forming equilateral triangles within the two-dimensional frequency search grid until the new equilateral triangle is a repeat of a previous equilateral triangle, at which time the triangulation search process reduces a size of the new equilateral triangle and restarts the process of sequentially forming equilateral triangles within the two-dimensional frequency search grid.

15. The method as recited in claim 14 , wherein the triangulation search process continues the process of sequentially forming equilateral triangles within the two-dimensional frequency search grid and reducing the size of the new equilateral triangle when it repeats the previous equilateral triangle until convergence criteria are satisfied.

16. The method as recited in claim 15 , wherein the convergence criteria includes a change of less than or equal to about 5% in the cost function values evaluated for sequential positions of a moving vertex within the two-dimensional frequency search grid, and wherein the convergence criteria includes the new equilateral triangle having a side length of less than or equal to about 5 kiloHertz within the two-dimensional frequency search grid, and wherein the convergence criteria includes a change in position of the moving vertex of less than or equal to about 1 kiloHertz in each frequency coordinate dimension of the two-dimensional frequency search grid.

17. A system for automated frequency tuning of a radiofrequency (RF) signal generator for operating in a multi-leve

Assignees

• Lam Res Corp

Inventors

• Evans Mathew
• Wu Ying
• Paterson Alexander

Classifications

• H01J37/32926

  Software, data control or modelling · CPC title

• H01J37/32183

  Matching circuits · CPC title

• H01J37/32155 Primary

  Frequency modulation · CPC title

• H01J37/32082 Primary

  Radio frequency generated discharge (H01J37/32357, H01J37/32366, H01J37/32394 and H01J37/32403 take precedence) · CPC title

• H01J37/32146 Primary

  Amplitude modulation, includes pulsing · CPC title