Spatially resolved optical emission spectroscopy (OES) in plasma processing
Disclosed is a method, system, and apparatus for optical emission measurement. The apparatus includes a collection system for collecting a plasma optical emission spectra through an optical window disposed at a wall of a plasma processing chamber. The optical system includes a mirror configured to scan a plurality of non-coincident rays across the plasma processing chamber; and a telecentric coupler for collecting an optical signal from a plasma and directing the optical signal to a spectrometer for measuring the plasma optical emission spectra.
1. An apparatus for optical emission measurement, the apparatus comprising:
a plasma processing chamber;
an optical window disposed on a wall of the plasma processing chamber; and
a collection system for collecting a plasma optical emission spectra through the optical window, the collection system including:
a mirror system configured to scan a plurality of non-coincident rays across the plasma processing chamber; and
a telecentric coupler for collecting an optical signal from a plasma and directing the optical signal to a spectrometer for measuring the plasma optical emission spectra, wherein a center of rotation of the plurality of non-coincident rays is substantially at the optical window.
2. The apparatus of claim 1 , wherein the telecentric coupler includes:
at least one collection lens; and
at least one coupling lens.
3. The apparatus of claim 2 , wherein the at least one collection lens or the at least one coupling lens are achromatic lenses.
4. The apparatus of claim 2 , wherein the telecentric coupler further includes:
an aperture disposed between the at least one collection lens and the at least coupling lens for defining a diameter of the plurality of non-coincident rays.
5. The apparatus of claim 1 , wherein the mirror system includes a scanning mirror.
6. The apparatus of claim 5 , wherein the scanning mirror is mounted on and scanned by a galvanometer scanning stage.
7. The apparatus of claim 5 , wherein the scanning mirror is mounted on and scanned by a stepper motor.
8. The apparatus of claim 5 , wherein the mirror system includes:
a transfer mirror;
a fold mirror; and
wherein the transfer mirror is configured to transfer the collected signal to the fold mirror and the fold mirror is configured to transfer the collected signal to a scanning mirror.
9. The apparatus of claim 1 , wherein the telecentric coupler includes:
a collection triplet lens configured to collect the optical signal from the mirror system; and
two coupling triplet lenses configured to focus the collected signal into an end of an optical fiber coupled to the spectrometer.
10. The apparatus of claim 1 , further comprising:
a second optical window; and
a second collection system for collecting the plasma optical emission spectra through the second optical window disposed at the wall of the plasma processing chamber, the second optical window having a center axis perpendicular to the center axis of the optical window.
11. The apparatus of claim 1 , wherein the collection system further includes:
a linear arc stage holding the mirror system, and the telecentric coupler, the linear arc stage being configured to move radially with respect to a center axis of the optical window causing the plurality of non-coincident rays to scan across the plasma processing chamber.
12. The apparatus of claim 11 , wherein the mirror system includes a fold mirror.
13. The apparatus of claim 1 , wherein the plurality of non-coincident rays are scanned 25° of a center axis of the optical window across the plasma processing chamber.
14. The apparatus of claim 1 , wherein the collection system has a low numerical aperture.
15. The apparatus of claim 1 , wherein the optical signal is collected from 21 non-coincident rays.
16. A system for plasma processing, comprising:
a plasma processing chamber;
an optical window disposed on a wall of the plasma processing chamber;
a collection system for collecting plasma optical emission spectra through the optical window;
a spectrometer coupled to the collection system for measuring the plasma optical emission spectra; and
wherein the collection system includes
a mirror system configured to scan a plurality of non-coincident rays across the plasma processing chamber, and
a telecentric coupler for collecting an optical signal from a plasma and directing the optical signal to the spectrometer, wherein a center of rotation of the plurality of non-coincident rays is substantially at the optical window.
17. A method for optical emission measurement, comprising:
depositing an optical window at a wall of a plasma processing chamber;
providing a collection system for collecting plasma optical emission spectra through the optical window, the collection system including a mirror system and a telecentric coupler;
scanning a plurality of non-coincident rays across the plasma processing chamber using the mirror system;
collecting an optical signal from a plasma via the telecentric coupler; and
directing the optical signal to a spectrometer for measuring the plasma optical emission spectra, wherein a center of rotation of the plurality of non-coincident rays is substantially at the optical window.
18. The method of claim 17 , wherein the mirror system includes at least a transfer mirror and a fold mirror.
19. The system of claim 16 , wherein the spectrometer is an ultra broadband high resolution spectrometer.
20. The system of claim 16 , wherein the plurality of non-coincident rays are scanned 30° of a center axis of the optical window across the plasma processing chamber.