SPATIALLY RESOLVED OPTICAL EMISSION SPECTROSCOPY (OES) IN PLASMA PROCESSING

• US 20150124250A1
• Filed: 10/31/2014
• Published: 05/07/2015
• Est. Priority Date: 11/01/2013
• Status: Active Grant

• Current Assignee: Tokyo Electron Limited
• Original Assignee: Tokyo Electron Limited
• Inventors: BAO, Junwei, MENG, Ching-Ling, TUITJE, Holger, CHEN, Yan, CHU, Hanyou, MIHAYLOV, Mihail, YAN, Zheng, ZOU, Haixing
• Granted Patent: US 9,970,818 B2
• Time in Patent Office: Days
• US Class Current: 356/316
• CPC Class Codes: G01J 3/443 Emission spectrometry
• CPC Class Codes: G01N 21/31 Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry G01N21/72 takes precedence
• CPC Class Codes: G01N 21/68 using high frequency electric fields
• CPC Class Codes: G01N 2201/10 Scanning

Abstract

Disclosed is a method, computer method, system, and apparatus for measuring two-dimensional distributions of optical emissions from a plasma in a semiconductor plasma processing chamber. The acquired two-dimensional distributions of plasma optical emissions can be used to infer the two-dimensional distributions of concentrations of certain chemical species of interest that are present in the plasma, and thus provide a useful tool for process development and also for new and improved processing tool development. The disclosed technique is computationally simple and inexpensive, and involves the use of an expansion of the assumed optical intensity distribution into a sum of basis functions that allow for circumferential variation of optical intensity. An example of suitable basis functions are Zernike polynomials.

Claims

1. A method for determining a spatial distribution of plasma optical emission, comprising:

igniting a plasma in a plasma processing chamber, the plasma processing chamber having a plasma optical emission measurement system, the plasma optical emission measurement system having a controller for controlling the plasma optical emission measurement system;

using the plasma optical emission measurement system, measuring N plasma optical emission spectra integrated along N non-coincident rays across the plasma processing chamber, where N>

1, each measured optical emission spectrum comprising M wavelengths, where M≧

1;

selecting, using the controller, an optical intensity distribution function I(r, θ

) comprising a sum of N basis functions F_p(r, θ

)

2. The method of claim 1, wherein the N basis functions F_p(r, θ

) are Zernike polynomials Z_p(r, θ

).

3. The method of claim 1, wherein the N basis functions F_p(r, θ

) are the N lowest order Zernike polynomials Z_p(r, θ

).

4. The method of claim 1, wherein the step of fitting N fitting parameters a_p comprises least squares fitting.

5. The method of claim 1, wherein the step of fitting N fitting parameters a_p comprises utilizing a predetermined optical collection efficiency.

6. The method of claim 5, wherein optical collection efficiency was determined by simulation.

7. The method of claim 5, wherein optical collection efficiency was determined experimentally.

8. The method of claim 1, wherein the plasma optical emission measurement system comprises:

N separate optical systems for each of N rays across the plasma processing chamber, each optical system collecting plasma optical emission spectra through at least one optical window disposed at a wall of the plasma processing chamber, and each optical system being coupled to a multi-channel spectrometer for measuring the plasma optical emission spectra.

9. The method of claim 8, wherein each optical system comprises:

a telecenter coupler for collecting an optical signal from the plasma and directing the optical signal to an end of an optical fiber for transmitting the optical signal to the multi-channel spectrometer.

10. The method of claim 9, wherein each telecenter coupler comprises:

at least one collection lens;

at least one coupling lens; and

an optional aperture.

11. The method of claim 10, wherein the at least one collection lens or the at least one coupling lens are achromatic lenses.

12. The method of claim 1, wherein the plasma optical emission measurement system comprises:

an optical system for collecting plasma optical emission spectra through an optical window disposed at a wall of the plasma processing chamber, the optical system comprising;

a scanning mirror configured to scan a plurality of non-coincident rays across the plasma processing chamber; and

a spectrometer coupled to the optical system for measuring the plasma optical emission spectra.

13. The method of claim 12, wherein the scanning mirror is mounted on and scanned by a galvanometer scanning stage.

14. The method of claim 12, wherein the scanning mirror is mounted on and scanned by a stepper motor.

15. The method of claim 12, wherein the optical system comprises:

a telecenter coupler for collecting an optical signal from the plasma and directing the optical signal to an end of an optical fiber for transmitting the optical signal to the spectrometer.

16. The method of claim 12, wherein the telecenter coupler comprises:

at least one collection lens;

at least one coupling lens; and

an optional aperture.

17. The method of claim 16, wherein the at least one collection lens or the at least one coupling lens are achromatic lenses.

18. A non-transitory machine-accessible storage medium having instructions stored thereon which cause a controller to perform a method for determining a spatial distribution of plasma optical emission, the method comprising:

igniting a plasma in a plasma processing chamber, the plasma processing chamber having a plasma optical emission measurement system, the plasma optical emission measurement system having a controller for controlling the plasma optical emission measurement system;

using the plasma optical emission measurement system, measuring N plasma optical emission spectra integrated along N non-coincident rays across the plasma processing chamber, where N>

1, each measured optical emission spectrum comprising M wavelengths, where M≧

1;

selecting, using the controller, an optical intensity distribution function I(r, θ

) comprising a sum of N basis functions F_p(r, θ

)

19. The storage medium of claim 18, wherein the N basis functions F_p(r, θ

) are Zernike polynomials Z_p(r, θ

).