Reducing speckle in an excimer light source

Patent metadata

Field	Value
Publication number	US-11054665-B2
Application number	US-201916503073-A
Country	US
Kind code	B2
Filing date	Jul 3, 2019
Priority date	Jan 16, 2017
Publication date	Jul 6, 2021
Grant date	Jul 6, 2021

Abstract

A method includes: producing a light beam made up of pulses having a wavelength in the deep ultraviolet range, each pulse having a first temporal coherence defined by a first temporal coherence length and each pulse being defined by a pulse duration; for one or more pulses, modulating the optical phase over the pulse duration of the pulse to produce a modified pulse having a second temporal coherence defined by a second temporal coherence length that is less than the first temporal coherence length of the pulse; forming a light beam of pulses at least from the modified pulses; and directing the formed light beam of pulses toward a substrate within a lithography exposure apparatus.

First claim

What is claimed is:

1. An optical source comprising:
a first stage light source configured to produce a seed light beam made up of pulses and including a spectral tuning apparatus configured to tune one or more spectral features of the seed light beam, each pulse having a wavelength in the deep ultraviolet range, each pulse having a first temporal coherence defined by a first temporal coherence length, and each pulse being defined by a pulse duration;
a coherence reduction system in the path of the seed light beam pulses and configured to, for each pulse of the seed light beam, produce a modified seed light beam pulse having a second temporal coherence defined by a second temporal coherence length that is less than the first temporal coherence length; and
a second stage optical amplifier including a resonator and a gain medium, the second stage optical amplifier configured to receive the modified seed light beam pulses output from the coherence reduction system, and to produce a light beam made up of amplified pulses.

2. The optical source of claim 1 , wherein the coherence reduction system comprises a phase modulator system configured to, for each pulse of the seed light beam, modulate an optical phase over the pulse duration of the pulse to produce the modified seed light beam pulse having the second temporal coherence defined by the second temporal coherence length that is less than the first temporal coherence length.

3. The optical source of claim 2 , wherein the phase modulator system includes a two-dimensional array of phase modulators.

4. The optical source of claim 2 , wherein the phase modulator system is also configured to, for each pulse of the seed light beam, reduce a spatial coherence of the pulse so that the modified pulse of the seed light beam has a second spatial coherence that is less than the spatial coherence of the seed light beam pulse.

5. The optical source of claim 2 , wherein the phase modulator system comprises a Pockels cell including a medium through which the seed light beam of pulses passes.

6. The optical source of claim 5 , wherein the phase modulator system is configured to, for each pulse of the seed light beam, modulate the optical phase over the pulse duration of the pulse to produce the modified seed light beam pulse including modulating the index of refraction of the medium of the Pockels cell.

7. The optical source of claim 2 , wherein the phase modulator system includes a single phase modulator.

8. The optical source of claim 1 , wherein the first stage light source includes a master oscillator including a gain medium in which amplification is configured to occur and an optical feedback mechanism and the second stage optical amplifier includes a power amplifier including a gain medium in which amplification is configured to occur when seeded with the seed light beam from the master oscillator.

9. The optical source of claim 8 , wherein the master oscillator includes a gas discharge chamber including two electrodes, and is configured to contain a laser gas that serves as the gain medium, wherein a laser resonator is formed between the spectral tuning apparatus on one side of the gas discharge chamber and an output coupler on a second side of the gas discharge chamber, the seed light beam exiting the first stage light source through the output coupler.

10. The optical source of claim 1 , wherein the coherence reduction system is configured to produce, for each seed light beam pulse, the modified seed light beam pulse having a bandwidth that is greater than a bandwidth of the seed light beam pulse.

11. A photolithography exposure apparatus comprising:
an optical arrangement configured to receive a light beam made up of pulses having a wavelength in the deep ultraviolet range, each pulse having a first temporal coherence defined by a first temporal coherence length and each pulse being defined by a pulse duration, wherein the optical arrangement comprises an illumination module, a reticle, and a projection stage aligned along an optical axis with a wafer stage; and
a coherence reduction system within the optical arrangement and in the path of the light beam pulses, the coherence reduction system configured to, for each pulse of the light beam, produce a modified light beam pulse having a second temporal coherence defined by a second temporal coherence length that is less than the first temporal coherence length.

12. The photolithography exposure apparatus of claim 11 , wherein the coherence reduction system comprises a phase modulator system configured to, for each pulse of the light beam, modulate an optical phase over the pulse duration of the pulse to produce the modified light beam pulse having the second temporal coherence defined by the second temporal coherence length that is less than the first temporal coherence length.

13. The photolithography exposure apparatus of claim 12 , wherein the phase modulator system includes a two-dimensional array of phase modulators.

14. The photolithography exposure apparatus of claim 12 , wherein the phase modulator system is also configured to, for each pulse of the light beam, reduce a spatial coherence of the pulse so that the modified pulse of the light beam has a second spatial coherence that is less than the spatial coherence of the light beam pulse.

15. The photolithography exposure apparatus of claim 12 , wherein the phase modulator system comprises a Pockels cell including a medium through which the light beam of pulses passes.

16. The photolithography exposure apparatus of claim 15 , wherein the phase modulator system is configured to, for each pulse of the light beam, modulate the optical phase over the pulse duration of the pulse to produce the modified light beam pulse including modulating the index of refraction of the medium of the Pockels cell.

17. The photolithography exposure apparatus of claim 11 , wherein the coherence reduction system is within the illumination module.

18. The photolithography exposure apparatus of claim 17 , wherein the illumination module includes a beam homogenizer and a conditioning device at the output of the beam homogenizer, and the coherence reduction system is inside the beam homogenizer.

19. The photolithography exposure apparatus of claim 18 , wherein the beam homogenizer includes an objective lenslet array and a field lenslet array, each lenslet array including a plurality of lenslets arranged in a plane that extends perpendicularly to the optical axis.

20. The photolithography exposure apparatus of claim 19 , wherein the coherence reduction system is near the objective lenslet array and the field lenslet array.

21. The photolithography exposure apparatus of claim 20 , wherein the coherence reduction system is between the objective lenslet array and the field lenslet array, and the coherence reduction system includes a two-dimensional array of phase modulators optically arranged in parallel with each other and arranged so that each phase modulator aligns with a pair of lenslets from the respective objective lenslet array and the field lenslet array.

Assignees

• Cymer LLC
• Asml Netherlands Bv

Inventors

• Op 'T Root Wilhelmus Patrick Elisabeth Maria
• Duffey Thomas Patrick
• Godfried Herman Philip
• Everts Frank
• Thornes Joshua Jon
• King Brian Edward

Classifications

• H01S3/225

  comprising an excimer or exciplex · CPC title

• H01S3/0085

  Modulating the output, i.e. the laser beam is modulated outside the laser cavity · CPC title

• G02F1/0121

  Operation of devices; Circuit arrangements, not otherwise provided for in this subclass · CPC title

• G02B19/0095

  for use with ultraviolet radiation · CPC title

• G03F7/70583

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