Metrology system and method having a plurality of sensors for estimating a spectral feature of a pulsed light beam

Patent metadata

Field	Value
Publication number	US-9778108-B2
Application number	US-201514720207-A
Country	US
Kind code	B2
Filing date	May 22, 2015
Priority date	May 22, 2015
Publication date	Oct 3, 2017
Grant date	Oct 3, 2017

Abstract

A metrology system includes an optical frequency separation apparatus in the path of the pulsed light beam and configured to interact with the pulsed light beam and output a plurality of spatial components that correspond to the spectral components of the pulsed light beam; a plurality of sensing regions that receive and sense the output spatial components; and a control system connected to an output of each sensing region. The control system is configured to: measure, for each sensing region output, a property of the output spatial components from the optical frequency separation apparatus for one or more pulses; analyze the measured properties including averaging the measured properties to calculate an estimate of the spectral feature of the pulsed light beam; and determine whether the estimated spectral feature of the pulsed light beam is within an acceptable range of values of spectral features.

First claim

What is claimed is:

1. A metrology system for measuring a spectral feature of a pulsed light beam, wherein the spectral feature is an aspect of the optical spectrum of the pulsed light beam, the metrology system comprising:
a single etalon in the path of the pulsed light beam and configured to interact with the pulsed light beam and output an interference pattern in the shape of a set of concentric rings that correspond to the spectral components of the pulsed light beam, wherein the single etalon includes a single pair of parallel reflecting surfaces that face each other and are separated by a constant distance;
a plurality of sensors that receive and sense the interference pattern, wherein each sensor of the plurality is arranged to extend across a plurality of the rings along a distinct sensing axis and interacts with only a portion of the interference pattern; and
a control system connected to an output of each sensor and configured to:
measure, for each sensor output, a property of the output spatial components from the etalon for one or more pulses;
analyze the measured properties including averaging the measured properties to calculate an estimate of the spectral feature of the pulsed light beam; and
determine whether the estimated spectral feature of the pulsed light beam is within an acceptable range of values of spectral features.

2. The system of claim 1 , further comprising a beam splitter in the path of the light beam, wherein the beam splitter:
directs a first percentage of the light beam toward the etalon, and
directs a second percentage of the light beam along the path of the light beam.

3. The system of claim 1 , wherein each sensor has the same performance parameters as the other sensors of the plurality.

4. The system of claim 1 , wherein the spectral feature is a bandwidth of the pulsed light beam.

5. The system of claim 1 , further comprising a spectral feature selection system optically connected to the pulsed light beam, wherein:
the control system is connected to the spectral feature selection system; and
if the control system determines that the estimated spectral feature of the pulsed light beam is outside the acceptable range, then the control system is configured to send an adjustment signal to the spectral feature selection system to modify the spectral feature of the pulsed light beam.

6. The system of claim 1 , wherein the range of one or more pulses is a single pulse.

7. The system of claim 1 , wherein averaging the measured properties comprises determining which measured property is the most accurate representation of the spectral feature and calculating the spectral feature of the pulsed light beam comprises selecting the measured property that most accurately represents the spectral feature.

8. The system of claim 1 , wherein:
the control system is configured to determine which of the measured properties fall inside a target range of values, and
the control system averages the measured properties to calculate an estimate by averaging only those measured properties that fall inside the target range of values.

9. The system of claim 1 , wherein averaging the measured properties comprises performing a weighted average of the measured properties and calculating the estimate of the spectral feature of the pulsed light beam comprises selecting the weighted average as the spectral feature estimate.

10. The system of claim 1 , wherein each sensor is a portion of a single detector that receives one or more entire spectral components.

11. The system of claim 1 , wherein each sensor of the plurality of sensors defines a sensing axis that is perpendicular to a direction of the outputted spatial components.

12. The system of claim 1 , wherein each sensor of the plurality of sensors is formed at a distinct location of a single detector placed at the output of the etalon.

13. The system of claim 1 , wherein single pair of parallel reflecting surfaces that face each other is formed on a pair of optical flats.

14. The system of claim 1 , wherein the single pair of parallel reflecting surfaces that face each other is formed on a single plate.

15. A method for measuring a bandwidth of a pulsed light beam, the method comprising:
dividing the pulsed light beam into a plurality of divided pulsed light beams;
for each divided pulsed light beam, transforming spectral information that includes spectral components of the divided pulsed light beam into spatial information that includes a plurality of spatial components, wherein the plurality of spatial components correspond to the spectral components of the divided pulsed light beam;
directing the plurality of spatial components toward a plurality of sensors;
sensing the plurality of spatial components at each of the sensors;
measuring, at each of the sensors, a property of the spatial components for one or more pulses of the divided pulsed light beam;
analyzing the measured properties including averaging the measured properties to calculate an estimate of the bandwidth of the pulsed light beam; and
determining whether the estimated bandwidth of the pulsed light beam is within an acceptable range of bandwidths.

16. The method of claim 15 , wherein sensing the plurality of spatial components at each of the plurality of sensors comprises sensing the plurality of spatial components at each of the plurality of sensors simultaneously for the same pulse of the light beam.

17. The method of claim 15 , further comprising, if it is determined that the estimated bandwidth of the pulsed light beam is outside the acceptable range, then modifying the bandwidth of the pulsed light beam.

18. The method of claim 15 , wherein averaging the measured properties comprises determining which measured property is the most accurate representation of the bandwidth and calculating the bandwidth of the pulsed light beam comprises selecting the measured property that most accurately represents the bandwidth.

19. The method of claim 15 , further comprising determining which of the measured properties fall inside a standard range of values,
wherein averaging the measured properties to calculate an estimate comprises averaging only those measured properties that fall inside the standard range of values.

20. The method of claim 15 , wherein averaging the measured properties comprises performing a weighted average of the measured properties and calculating the estimate of the bandwidth of the pulsed light beam comprises selecting the weighted average as the bandwidth estimate.

21. The method of claim 15 , wherein measuring, at each of the sensors, the property of the spatial components for one or more pulses of the divided pulsed light beam comprises measuring the property of the output spatial components for each of the sensors using the same measurement technique.

22. An optical system comprising:
an optical source including at least one gain medium that produces a pulsed light beam;
a beam splitter that directs a first portion of the pulsed light beam along a metrology path and directs a second portion of the pulsed light beam along a lithography path,
a metrology system in the metrology path, the metrology system comprising:
a means for transforming spectral information of the pulsed light beam into an interference pattern in the shape of a set of concentric rings, wherein the transforming means is in the path of the pulsed light beam and is configured to interact with the pulsed light beam;
a plurality of sensors that r

Assignees

• Cymer LLC

Inventors

• Thornes Joshua

Classifications

• G01J3/027

  Control of working procedures of a spectrometer; Failure detection; Bandwidth calculation · CPC title

• G01J3/18

  using diffraction elements, e.g. grating (gratings per se G02B) · CPC title

• G01J3/2803 Primary

  using photoelectric array detector · CPC title

• G01J3/26 Primary

  using multiple reflection, e.g. Fabry-Perot interferometer, variable interference filters · CPC title

• G01J9/00

  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