Adjusting an amount of coherence of a light beam

Patent metadata

Field	Value
Publication number	US-9945730-B2
Application number	US-201615256196-A
Country	US
Kind code	B2
Filing date	Sep 2, 2016
Priority date	Sep 2, 2016
Publication date	Apr 17, 2018
Grant date	Apr 17, 2018

Abstract

Techniques for controlling an optical system include accessing a measured value of a property of a particular pulse of a pulsed light beam emitted from the optical system, the property being related to an amount of coherence of the light beam; comparing the measured value of the property of the light beam to a target value of the property; determining whether to generate a control signal based on the comparison; and if a control signal is generated based on the comparison, adjusting the amount of coherence in the light beam by modifying an aspect of the optical system based on the control signal to reduce an amount of coherence of a pulse that is subsequent to the particular pulse.

First claim

What is claimed is:

1. A method of controlling an optical system, the optical system comprising two or more resonator optical elements that define a resonator cavity, the resonator cavity comprising a gain medium between at least two of the two or more resonator optical elements, the method comprising:
accessing a measured value of a property of a particular pulse of a pulsed light beam emitted from the optical system, the property being related to an amount of coherence of the light beam;
comparing the measured value of the property of the light beam to a target value of the property;
determining whether to generate a control signal based on the comparison; and
if a control signal is generated based on the comparison, adjusting the amount of coherence in the light beam by modifying an aspect of the resonator cavity based on the control signal to reduce an amount of coherence of a pulse that is subsequent to the particular pulse.

2. The method of claim 1 , wherein the property of the light beam comprises a divergence of the light beam.

3. The method of claim 2 , wherein the divergence of the light beam is measured outside of the optical system or outside of the resonator cavity.

4. The method of claim 1 , wherein the pulse that is subsequent to the particular pulse is a pulse that immediately follows the particular pulse.

5. The method of claim 1 , wherein adjusting the amount of coherence in the light beam by modifying an aspect of the resonator cavity based on the control signal comprises applying the control signal to at least one of the two or more resonator optical elements that define the resonator cavity, the at least one resonator optical element comprising an optical surface that interacts with the light beam in the resonator cavity to at least partially determine the value of the property of the light beam emitted from the optical system, the application of the control signal being sufficient to move the optical surface.

6. The method of claim 5 , wherein the application of the control signal being sufficient to move the optical surface comprises the application of the control signal being sufficient to change the shape of the optical surface, change the position of the optical surface, change the angle of the optical surface relative to a direction of propagation of the pulsed light beam, or change a curvature of the optical surface.

7. The method of claim 5 , wherein the optical surface comprises a plurality of portions, and application of the control signal is sufficient to move at least one of the plurality of portions of the optical surface relative to at least one of the other portions.

8. The method of claim 1 , further comprising:
determining an operating condition of the optical system, the operating condition being associated with one or more operating parameters,
if a control signal is not generated based on the comparison, declaring the measured value of the property of the light beam as a desired value of the property for the determined operating condition.

9. The method of claim 8 , wherein declaring the measured value of the property of the light beam as a desired value of the property for the determined operating condition comprises storing data comprising the measured value in association with the operating parameters of the operating condition.

10. The method of claim 9 , wherein the operating parameters comprise any of a pressure of the gain medium of the resonator cavity, a temperature of the gain medium of the resonator cavity, a repetition rate of the light beam emitted from the optical system, an amount of force applied to an optical element comprising an optical surface that interacts with the light beam in the resonator cavity to at least partially determine the value of the property of the light beam emitted from the optical system, and an amount of force applied to an optical element comprising an optical surface that interacts with the light beam in the optical system to at least partially determine the value of the property of the light beam emitted from the optical system.

11. The method of claim 10 , further comprising:
receiving an indication of a change in the operating condition of the optical system to a current operating condition;
determining the desired value of the property for the current operating condition from the stored data; and
setting the target value to the determined desired value.

12. The method of claim 11 , wherein the indication of a change in the operating condition of the optical system comprises an indication of a change in the repetition rate of the light beam emitted from the optical system to a new repetition rate, and
the indication of the change in the repetition rate is received from a lithography exposure apparatus that receives the light beam from the optical system.

13. The method of claim 1 , wherein accessing a measured value of a property of a light beam comprises measuring the value of the property of the light beam at a first time, and further comprising:
measuring the value of the property of the light beam at a second time, the second time occurring after the first time and after adjusting the amount of coherence in the light beam;
comparing the value of the property of the light beam at the second time to the target value; and
determining whether to generate a second control signal based on the comparison of the value of the property of the light beam at the second time to the target value.

14. The method of claim 1 , wherein modifying an aspect of the resonator cavity comprises changing a geometry of the resonator cavity.

15. The method of claim 14 , wherein the resonator cavity receives a seed light beam from a master oscillator, and the optical system provides the light beam to a photolithography system.

16. A method of controlling an optical system, the method comprising:
obtaining a value of a property of a light beam emitted from an optical system at a plurality of operating conditions, the obtained value of the property being associated with an amount of coherence in the light beam, and each of the operating conditions being associated with one or more operating parameters and status information related to an optical element, the optical element comprising an optical surface that interacts with the light beam to at least partially determine the obtained value of the property of the light beam;
storing the obtained value of the property and the status information related to the optical element for each operating condition as stored data;
operating the optical system at a current operating condition, the current operating condition being associated with current values of one or more of the operating parameters and a current status information related to the optical element;
receiving an indication of a change in the current operating condition of the optical system, the indication of a change comprising a new value of one or more of the operating parameters;
determining status information related to the optical element associated with the new value from the stored data; and
applying a command signal based on the determined status information to the optical element.

17. The method of claim 16 , wherein the obtained value of the property of the light beam is associated with an acceptable amount of coherence in the light beam for each of the plurality of operating conditions, and further comprising:
obtaining another value of the property of the light beam by measuring the value of the property of the light beam after applying the command signal based on the determined status in

Assignees

• Cymer LLC

Inventors

• Bibby Thomas Frederick Allen
• Thornes Joshua Jon
• Rokitski Rostislav
• Duffey Thomas Patrick

Classifications

• G02B27/0988

  Diaphragms, spatial filters, masks for removing or filtering a part of the beam · CPC title

• G01J9/00 Primary

  Measuring optical phase difference (devices or arrangements for controlling the phase of light beams G02F1/01); Determining degree of coherence; Measuring optical wavelength (spectrometry G01J3/00) · CPC title

• G01J2009/006

  using pulses for physical measurements · CPC title

• G03F7/70583

  Speckle reduction, e.g. coherence control or amplitude/wavefront splitting · CPC title

• G01J1/4257 Primary

  applied to monitoring the characteristics of a beam, e.g. laser beam, headlamp beam (monitoring arrangements for lasers in general H01S3/0014) · CPC title