Spatially resolved optical emission spectroscopy (OES) in plasma processing

Patent metadata

Field	Value
Publication number	US-9970818-B2
Application number	US-201414530164-A
Country	US
Kind code	B2
Filing date	Oct 31, 2014
Priority date	Nov 1, 2013
Publication date	May 15, 2018
Grant date	May 15, 2018

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.

First claim

What is claimed is:

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 each of N respective 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)

I
⁡

(

r
,
θ

)

=

∑

p
=
1

N

⁢

a
p

⁢

F
p

⁡

(

r
,
θ

)

wherein at least one of the N basis functions F p (r, θ) varies with both radial location r and circumferential location θ inside the plasma processing chamber, and wherein each of the N basis functions F p (r, θ) is associated with a fitting parameter α p ; and
determining, using the controller, a spatial distribution of plasma optical emission for each of the M wavelengths by fitting the N fitting parameters α p of the selected optical intensity distribution function I(r, θ), to fit the selected optical intensity distribution function I(r, θ) to the N measured plasma optical emission spectra, wherein the step of fitting N fitting parameters α p comprises utilizing an optical collection efficiency w for each one of the N non-coincident rays, each optical collection efficienc being adapted to each ray by performing a simulation or an experiment which determines the efficiency of coupling of light from a given location within each one of the N non-coincident rays to a respective optical fiber connected to a spectrometer.

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 α p comprises least squares fitting.

5. The method of claim 1 , wherein optical collection efficiency was determined by simulation.

6. The method of claim 1 , wherein optical collection efficiency was determined experimentally.

7. 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 spectro er for measuring the plasma optical emission spectra.

8. The method of claim 7 , 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.

9. The method of claim 8 , wherein each telecenter coupler comprises:
at least one collection lens;
at least one coupling lens; and
an optical aperture.

10. The method of claim 9 , wherein the at least one collection lens or the at least one coupling lens are achromatic lenses.

11. 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 from within the processing chamber, across the plasma processing chamber; and

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

12. The method of claim 11 , wherein the scanning mirror is mounted on and scanned by a galvanometer scanning stage.

13. The method of claim 11 , wherein the scanning mirror is mounted on and scanned by a stepper motor.

14. The method of claim 11 , 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.

15. The method of claim 11 , wherein the telecenter coupler comprises:
at least one collection lens;
at least one coupling lens; and
an optional aperture.

16. The method of claim 15 , wherein the at least one collection lens or the at least one coupling lens are achromatic lenses.

17. The method of claim 1 , wherein each optical collection efficiency w is adapted to each ray by performing a calibration, wherein light sources are moved along each ray to separately determine the efficiency for each ray of coupling light to an optical fiber connected to a spectrometer.

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 each of N respective 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)

I
⁡

(

r
,
θ

)

=

∑

p
=
1

N

⁢

Assignees

• Tokyo Electron Ltd

Inventors

• Bao Junwei
• Meng Ching-Ling
• Tuitje Holger
• Mihaylov Mihail
• Chen Yan
• Yan Zheng
• Zou Haixing
• Chu Hanyou

Classifications

• G01N2201/10

  Scanning · CPC title

• G01J3/443 Primary

  Emission spectrometry · CPC title

• G01N21/68

  using high frequency electric fields · CPC title

• G01N21/31

  Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry {(G01N21/72 takes precedence)} · CPC title