Residual gain monitoring and reduction for EUV drive laser

Patent metadata

Field	Value
Publication number	US-10524345-B2
Application number	US-201815946316-A
Country	US
Kind code	B2
Filing date	Apr 5, 2018
Priority date	Apr 28, 2017
Publication date	Dec 31, 2019
Grant date	Dec 31, 2019

Abstract

A laser system includes a laser source operable to provide a laser beam; a laser amplifier having an input port and an output port and operable to amplify the laser beam, the laser beam travelling along a main beam path through the laser amplifier from the input port to the output port; and a residual gain monitor operable to provide a probe laser beam, the probe laser beam travelling along a probe beam path through the laser amplifier from the output port to the input port, wherein the residual gain monitor calculates a residual gain of the laser amplifier according to the probe laser beam.

First claim

What is claimed is:

1. A system, comprising:
a laser source operable to provide a laser beam;
a laser amplifier having an input port and an output port and operable to amplify the laser beam, the laser beam travelling along a main beam path through the laser amplifier from the input port to the output port; and
a residual gain monitor operable to provide a probe laser beam, the probe laser beam travelling along a probe beam path through the laser amplifier from the output port to the input port and returning to the residual gain monitor, wherein the residual gain monitor is operable to calculate a residual gain of the laser amplifier using the probe laser beam.

2. The system of claim 1 , further comprising:
an extreme ultraviolet (EUV) vessel operable to receive the laser beam after travelling through the laser amplifier for interaction with a target to create EUV light.

3. The system of claim 1 , further comprising a probe laser beam delay line, wherein the probe laser beam delay line is configured to adjust a time interval between when the laser beam and the probe laser beam entering the laser amplifier.

4. The system of claim 1 , wherein:
the probe beam path is offset from the main beam path in the laser amplifier; and
the probe laser beam travels through the laser amplifier in parallel with the laser beam.

5. The system of claim 1 , wherein:
the probe beam path overlaps with the main beam path in the laser amplifier in a diagonal direction; and
the probe laser beam travels through the laser amplifier during a period when there is no laser beam in the laser amplifier.

6. The system of claim 5 , wherein:
a portion of the laser beam is reflected after having passed the laser amplifier, resulting in a reflected laser beam; and
the probe laser beam travels through the laser amplifier before the reflected laser beam enters the laser amplifier.

7. The system of claim 1 , wherein a power level of the probe laser beam before the probe laser beam enters the laser amplifier is in a range from about 10 −9 to about 10 −6 of a power level of the laser beam before the laser beam enters the laser amplifier.

8. The system of claim 1 , further comprising:
a reflecting component allowing the laser beam to travel through the laser amplifier more than once.

9. The system of claim 8 , wherein the reflecting component also allows the probe laser beam to travel through the laser amplifier more than once.

10. The system of claim 8 , wherein the reflecting component changes a polarization direction of the laser beam by 90°.

11. A system, comprising:
a laser source generating a laser pulse, the laser pulse traveling along a laser path;
an extreme ultraviolet (EUV) vessel receiving the laser pulse for creating EUV light and reflecting a portion of the laser pulse as a reflected laser pulse;
a first gain medium located between the laser source and the EUV vessel along the laser path;
a second gain medium located between the first gain medium and the EUV vessel along the laser path, wherein the reflected laser pulse travels through the second gain medium and the first gain medium along the laser path;
a first residual gain monitoring module generating a first probe laser pulse, the first probe laser pulse traveling through the first gain medium along a first probe path, the first residual gain monitoring module generating a first residual gain data according to the first probe laser pulse;
a second residual gain monitoring module generating a second probe laser pulse, the second probe laser pulse traveling through the second gain medium along a second probe path, the second residual gain monitoring module generating a second residual gain data according to the second probe laser pulse; and
a control module coupled to the first and second residual gain monitoring modules to receive the first and second residual gain data and adjusting parameters of the first and second gain mediums according to a comparison to a threshold level.

12. The system of claim 11 , wherein:
the first probe path overlaps with the laser path in the first gain medium; and
the second probe path overlaps with the laser path in the second gain medium.

13. The system of claim 12 , wherein:
the first probe laser pulse travels through the first gain medium during an interval after the laser pulse leaves the first gain medium and before the reflected laser pulse enters the first gain medium; and
the second probe pulse travels through the second gain medium during an interval after the laser pulse leaves the second gain medium and before the reflected laser pulse enters the second gain medium.

14. The system of claim 11 , wherein:
the first probe path is offset from the laser path in the first gain medium; and
the second probe path is offset from the laser path in the second gain medium.

15. The system of claim 11 , wherein the second gain medium has a cross-sectional area perpendicular to the laser path larger than that of the first gain medium, further comprising:
a beam shaping component located between the first gain medium and the second gain medium, the beam shaping component enlarging a cross-sectional area of the laser pulse.

16. The system of claim 11 , wherein the laser pulse travels through the first gain medium more than once before entering the second gain medium.

17. The system of claim 11 , wherein parameters of the first and second gain mediums include RF power, mixture gas pressure, mixture gas ratio, or a combination thereof.

18. A method, comprising:
generating a laser beam in a laser source;
passing the laser beam through a laser amplifier along a main beam path, such that the laser beam is amplified, the laser beam exiting the laser amplifier from a terminal of the laser amplifier;
generating a probe laser beam in a residual gain monitor;
passing the probe laser beam through the laser amplifier along a probe beam path, such that the probe laser beam is amplified, the probe laser beam entering the laser amplifier from the terminal of the laser amplifier; and
calculating a residual gain of the laser amplifier based on strengths of the probe laser beam before and after being amplified.

19. The method of claim 18 , wherein the probe beam path is offset from the main beam path in the laser amplifier, the passing of the probe laser beam through the laser amplifier includes passing the probe laser beam through the laser amplifier simultaneously with the passing of the laser beam through the laser amplifier.

20. The method of claim 18 , wherein the probe beam path overlaps with the main beam path in the laser amplifier, the passing of the probe laser beam through the laser amplifier includes passing the probe laser beam through the laser amplifier during a period when the laser beam is not in the laser amplifier.

Assignees

• Taiwan Semiconductor Mfg Co Ltd

Inventors

• Chang Chun-Lin Louis
• Yeh Jen-Hao
• Chang Han-Lung
• Fu Tzung-Chi
• Liu Bo-Tsun
• Chen Li-Jui
• Cheng Po-Chung

Classifications

• H01S3/1305

  Feedback control systems · CPC title

• H01S3/10038

  Amplitude control · CPC title

• H01S3/104

  in gas lasers · CPC title

• H01S3/2333

  Double-pass amplifiers · CPC title

• H01S3/134

  in gas lasers · CPC title